JP2007218894A - Gas sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor element for preventing water-induced cracks and securing early activation. <P>SOLUTION: The gas sensor element 1 comprises a solid electrolyte body 2 of oxygen ion conductivity, an electrode 21 on the measured gas side disposed on one surface of the solid electrolyte body 2, an electrode 22 on the reference gas side formed on the other surface of the solid electrolyte body 2, and a heater section 3 laminated on the solid electrolyte body 2. The heater section 3 is formed by forming a heating element 31 for generating heat with current carry on the heater substrate 32, and the heater substrate 32 is laminated on the solid electrolyte body 2. The gas sensor element 1 comprises a porous protective layer 4 formed so as to cover a region exposed to the measured gas on its surface, of a gas inlet 11 for introducing the measured gas into the electrode 21 on the measured gas side. A protective layer non-forming section 5 that does not form the porous protective layer 4 is arranged in at least a part of a heating element side corner 33, which is a side corner of the heater substrate 32 in a region corresponding to the axial length of the heating element 31. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas sensor element for detecting a specific gas concentration in a gas to be measured.

Conventionally, a gas sensor element for detecting a specific gas concentration in a measured gas such as exhaust gas by providing a measured gas side electrode on one surface of the solid electrolyte body and a reference gas side electrode on the other surface has been provided. is there. The gas sensor element is provided with a porous protective layer so as to cover a gas inlet for introducing the measurement gas in order to protect the measurement gas side electrode from poisonous substances contained in the measurement gas such as exhaust gas. ing.
Since this porous protective layer is formed by dipping and adhering the tip of the gas sensor element in a ceramic slurry, it is basically formed over the entire circumference of the tip of the gas sensor element.

  Further, the exhaust gas of the internal combustion engine contains water droplets generated by the combustion of the fuel. If these water droplets or the like adhere to the ceramic gas sensor element, particularly the heater part, which is at a high temperature when the gas sensor is used, it adheres. The temperature of the affected part rapidly decreases, and a temperature difference is generated between it and the surrounding area. The stress due to this may cause cracks, cracks, etc. in the ceramic, leading to disconnection of the heating element.

  In other words, the gas sensor element is heated by a built-in heater unit. At this time, if water droplets flying together with the gas to be measured adhere to the surface of the gas sensor element, the element may be cracked. In particular, when the water is applied to the side corners of the heater substrate close to the heating element of the heater part, a large temperature difference can be generated between the heater and the surroundings, and stress is likely to be concentrated, leading to element cracking.

  When the present inventors observed the occurrence of cracks due to the adhesion of water droplets, the water droplets adhering to the porous protective layer were instantly absorbed and diffused by the water retention of the porous protective layer, and the temperature around the adhered portion suddenly increased. It was found that the water resistance of the porous protective layer was lowered. If a porous protective layer is also formed on the side corners of the heater substrate where element cracking is likely to occur as described above, it is considered that water cracking is particularly likely to occur when the side corners are covered with water.

On the other hand, it was found that the one without the porous protective layer was excellent in water resistance. In the absence of a porous protective layer, the water droplets adhering to the sensor element surface are almost free from spreading on the element surface due to the Leidenfrost phenomenon. Compared with the case where there is a protective layer, it can be suppressed to a very small size, and as a result, it is considered that a gas sensor element in which cracks are unlikely to occur when water droplets adhere thereto is considered.
The Leidenfrost phenomenon is a phenomenon in which when a water droplet comes into contact with the high temperature portion of the surface of the gas sensor element, the surface of the water droplet instantly evaporates and the evaporated water vapor layer acts as a heat insulating layer between the element surface and the water droplet. .

On the other hand, in order to prevent water cracking, a gas protective element having a porous protective layer formed all around is disclosed (Patent Document 1). However, as described above, since the porous protective layer has a water retention effect, forming the porous protective layer at the side corners of the heater substrate tends to cause water cracking.
Further, if the thickness of the porous protective layer is increased, the attached water droplets can be dispersed in the surface direction so that the water droplets do not reach the element surface, so that water cracking can be suppressed. However, in this case, the heat capacity of the gas sensor element is increased, and the rapid thermal performance is reduced. This hinders early activation of the gas sensor element, and there is a problem that it is difficult to accurately detect the gas concentration when the engine is started.

JP 2003-322632 A

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a gas sensor element that prevents water cracking and ensures early activity.

The first invention includes an oxygen ion conductive solid electrolyte body, a gas side electrode to be measured provided on one surface of the solid electrolyte body, and a reference gas side electrode formed on the other surface of the solid electrolyte body. A gas sensor element having a heater portion laminated on the solid electrolyte body,
The heater portion is formed by forming a heating element that generates heat upon energization on the heater substrate, and the heater substrate is laminated on the solid electrolyte body.
The gas sensor element has a porous protective layer formed on the surface so as to cover at least a region exposed to the gas to be measured among gas inlets for introducing the gas to be measured to the gas to be measured side electrode. ,
In addition, a protective layer non-forming portion that does not form the porous protective layer is disposed on at least a part of a side portion of the heating element that is a side corner portion of the heater substrate in a region corresponding to the axial length of the heating element. It is in the gas sensor element characterized by the above-mentioned (Claim 1).

Next, the effects of the present invention will be described.
In the gas sensor element, the porous protective layer is formed so as to cover at least a region of the gas inlet that is exposed to the gas to be measured. Thereby, the poisoning substance contained in the measurement gas can be removed, and the measurement gas side electrode can be prevented from being poisoned.
And the said protective layer non-formation part which does not form the said porous protective layer is arrange | positioned in the at least one part of the said heat generating body side corner part. Thereby, a moisture crack can be suppressed effectively.

That is, the mechanism of the effect of suppressing water cracking can be considered as follows.
As described above, the side portion of the heating element is a portion where thermal stress is particularly likely to be concentrated when exposed to water.In the gas sensor element of the present invention, a porous protective layer is provided on the portion where thermal stress is likely to be concentrated. A “protective layer non-formation portion”, which is a portion that is not formed, is provided.

  The protective layer non-forming portion does not have water retention, and even if water droplets adhere to the protective layer non-forming portion, the water droplets instantaneously leave the surface of the element due to the Leidenfrost phenomenon described above, and Temperature drop can be suppressed. Therefore, water cracking can be effectively prevented by disposing the protective layer non-forming portion in the side portion of the heating element.

  In the gas sensor element, the porous protective layer is not provided on the entire circumference, and it is not particularly necessary to increase the thickness of the porous protective layer. Therefore, the heat capacity of the gas sensor element can be kept small, and quick heat performance can be ensured. Thereby, the early activation of a gas sensor element is securable.

  As described above, according to the present invention, it is possible to provide a gas sensor element that prevents water cracking and ensures early activity.

The second invention includes an oxygen ion conductive solid electrolyte body, a gas side electrode to be measured provided on one surface of the solid electrolyte body, and a reference gas side electrode formed on the other surface of the solid electrolyte body. A gas sensor element having a heater portion laminated on the solid electrolyte body,
The heater portion is formed by forming a heating element that generates heat upon energization on the heater substrate, and the heater substrate is laminated on the solid electrolyte body.
The gas sensor element has a porous protective layer formed on the surface so as to cover at least a region exposed to the gas to be measured among gas inlets for introducing the gas to be measured to the gas to be measured side electrode. ,
Further, the protective layer non-forming portion that does not form the porous protective layer is a surface opposite to the side where the heater portion is provided in a region corresponding to the axial length of the heating element, and the gas introduction port The gas sensor element is arranged in at least a part of a portion excluding the above (Claim 2).

Next, the effects of the present invention will be described.
In the gas sensor element, a protective layer non-forming portion without a porous protective layer is disposed on the surface opposite to the side where the heater portion is provided. Therefore, when the surface opposite to the side where the heater is provided is wetted, water droplets can be instantaneously detached from the element surface, suppressing the temperature drop on the element surface, and suppressing element cracking. Can do. In addition, since the amount of the porous protective layer formed is reduced, the heat capacity of the gas sensor element can be reduced to facilitate early activation.

  As described above, according to the present invention, it is possible to provide a gas sensor element that prevents water cracking and ensures early activity.

  In the first invention (invention 1), the side corner portion of the heater substrate is a corner portion of a side end portion of the surface opposite to the solid electrolyte body of the heater substrate, and the gas sensor element. It is also the side corner. In some cases, a chamfered portion is formed in the side corner portion, and the chamfered portion is also included in the side corner portion.

In addition, as the gas sensor element, for example, an A / F sensor element that is installed in an exhaust pipe of an internal combustion engine for various vehicles such as an automobile engine and detects an oxygen concentration in the exhaust gas for use in an exhaust gas feedback system. And an O ₂ sensor element, or a NOx sensor element for detecting a NOx concentration used for detecting deterioration of a three-way catalyst installed in an exhaust pipe.
In the present specification, the “front end side” refers to the side of the gas sensor element that is inserted into the exhaust pipe or the like, and the opposite side is referred to as the “base end side”.

  The porous protective layer is preferably not formed on the surface of the gas sensor element other than the gas inlet as much as possible. If many porous protective layers are formed, the probability of water cracking increases, and the early activation of the gas sensor element is hindered. Therefore, ideally, the porous protective layer is preferably provided only at the gas inlet.

Next, in the second aspect of the present invention (invention 2), the protective layer non-forming portion is formed on a side of the heating element that is a side corner of the heater substrate in a region corresponding to the axial length of the heating element. It is preferable that they are also arranged at least in part (claim 3).
In this case, both the operational effects of the second invention and the operational effects of the first invention can be obtained. Therefore, it is possible to provide a gas sensor element that ensures further prevention of water cracking and early activation.

Moreover, it is preferable that the said protective layer non-formation part is arrange | positioned in the whole said heat generating body side corner part (Claim 4).
In this case, water cracking can be prevented more reliably. That is, basically, the heat generating body side corners are liable to concentrate thermal stress due to water and easily generate cracks. It can be surely prevented.

Further, it is preferable that the protective layer non-formation portion is disposed at a side corner portion of the heater substrate in 60% or more of the length region exposed to the gas to be measured.
In this case, water cracking can be prevented more reliably. That is, there is a possibility that the area exposed to the gas to be measured is exposed to water at any position. And not only the said heat generating body side corner part but the side corner part of a heater board | substrate is a part where stress concentration tends to be easy. Therefore, water cracking can be more effectively prevented by disposing the protective layer non-forming portion in the side corner portion of the heater substrate in 60% or more of the possible length region of water. .

Moreover, it is preferable that the said protective layer non-formation part is also arrange | positioned also at the front-end | tip corner | angular part of the said heater substrate in the front-end | tip part of the said gas sensor element.
In this case, it is possible to reliably prevent water cracking at the tip corner of the heater substrate.

Also, the distance in the stacking direction from the heating element side corner to the end of the protective layer non-forming portion on the side surface of the gas sensor element is a, and the surface on the opposite side of the gas sensor element from the heating element side corner is the surface of the gas sensor element. When the distance in the stacking direction up to b is b, a / b is preferably 0.05 or more.
In this case, water cracking can be sufficiently prevented.
When the a / b is less than 0.05, the porous protective layer is present in a portion close to the side portion of the heating element, and thermal stress is exerted on the side portion of the heating element due to water droplets held in the porous protection layer. May cause cracks. Therefore, the effect of preventing water cracking can be sufficiently obtained by disposing the non-protective layer forming portion in a region from the heating element side corner portion to a position separated by 5% or more of the distance b.

Further, the distance in the width direction from the heating element side corner to the end of the protective layer non-forming portion on the surface of the gas sensor element on the heater portion side is c, and the width of the surface of the gas sensor element on the heater portion side is d. C / d is preferably 0.02 or more (claim 8).
Also in this case, the effect of preventing water cracking can be sufficiently obtained as in the case of the invention of claim 7.

The porous protective layer preferably contains γ-alumina, θ-alumina, or titania as a main component (claim 9).
In this case, poisonous substances in the measurement gas can be effectively trapped.
Even when a catalyst is contained in the porous protective layer, trapping poisonous substances is effective by using γ-alumina, θ-alumina, or titania having a large specific surface area as the main component of the porous protective layer. Can be done. Further, the heat resistance of the catalyst can be ensured. When the porous protective layer has the same particle size and the same thickness when the specific surface area is larger, the distance between the catalysts can be increased and the supporting force can be increased, so that the aggregation of the catalyst due to heat can be suppressed. The durability of the catalyst function can be improved.

Further, the porous protective layer is formed in a plurality of layers, and it is preferable that the particle diameter is larger as the layer is farther from the surface of the gas sensor element.
In this case, various poisonous substances having different particle sizes can be effectively trapped. That is, trapping poisonous substances having a large particle diameter in a layer far from the surface of the gas sensor element and trapping poisonous substances having a small particle diameter in a layer near the surface of the gas sensor element enables effective trapping.

In addition, when a poisonous substance such as an oxide such as Zn, Ca, and P is deposited, the porous protective layer is likely to be clogged if it has a single layer structure. By configuring the diameter, the deposited solid poison is deposited on the surface of the large particles and trapped. And since the particle space of this large particle is large, it is hard to cause clogging. Thereby, since the amount of deposition on the inner layer of the poisonous substance deposited in a solid state can be greatly reduced, clogging can be effectively suppressed.
Of course, when the porous protective layer sufficiently functions, it may be composed of one layer.

The porous protective layer is composed of two layers, and the inner first protective layer has a smaller particle size than the outer second protective layer, and the average particle size of the first protective layer is 1 to 40 μm. In addition, the average particle size of the second protective layer may be 2 to 100 μm.
In this case, it is possible to obtain a good collection effect of gasoline additives such as Pb and S, gaseous poisons of the above oil additives, and oil additives such as Ca, P, Si and Zn.

  When the average particle diameter of the first protective layer is smaller than 1 μm, the space between the particles becomes small, and therefore, when a gaseous poison is deposited, clogging is likely to occur with a small amount of the poison. Moreover, since gas permeability falls, there exists a possibility that an initial response may fall. On the other hand, when the average particle size of the first protective layer is larger than 40 μm, the trapping property of the gaseous poison is lowered, the poison passes through the porous protective layer, and the diffusion resistance layer is clogged. Or may be deposited on the measured gas side electrode.

  In addition, when the average particle size of the second protective layer is smaller than 2 μm, the space between the particles becomes small, so when the oil additive is deposited, the space is filled with a small amount of deposition, Clogging is likely to occur, and there is a risk of problems such as a decrease in sensor output due to a decrease in gas permeability. On the other hand, when the average particle diameter of the second protective layer exceeds 100 μm, the space between the particles becomes too large, and it is difficult to obtain a sufficient trapping effect. There is a risk of clogging.

Preferably, at least one of the porous protective layers is a catalyst layer containing a catalyst made of a noble metal or a metal oxide.
In this case, the poisonous substance in the measurement gas can be sufficiently trapped in the porous protective layer. And the trapped poisonous substance can be decomposed. In addition, hydrogen gas in the measurement gas can be burned in the porous protective layer, and the detection accuracy of the specific gas concentration by the gas sensor element can be improved.
Here, for example, Pt, Rh, Ru, Pd and the like can be used as the noble metal catalyst, and for example, titania (TiO ₂ ) and the like can be used as the metal oxide catalyst.

The catalyst is preferably made of at least one precious metal of Pt, Rh, Pd, and Ru (claim 13).
In this case, poisonous substances can be collected more efficiently in the porous protective layer.

The catalyst is preferably made of a noble metal having an average particle size of 0.01 to 5 μm.
In this case, it is possible to obtain a catalyst layer that is excellent in durability and sufficiently exhibits the catalyst function.
When the average particle size is less than 0.01 μm, the change in the catalyst function before and after the endurance is large, and the sensor output of the gas sensor element may vary. On the other hand, when the average particle size exceeds 5 μm, the specific surface area of the catalyst is decreased, and it may be difficult to sufficiently exhibit the catalyst function.

The catalyst is preferably made of a noble metal having an average particle size of 0.1 to 2 μm.
In this case, a catalyst layer that is excellent in durability and sufficiently exhibits a catalyst function can be obtained more reliably.

The catalyst preferably contains at least titania.
In this case, poisonous substances can be sufficiently collected in the catalyst layer.

The catalyst layer preferably has a catalyst content of 10 μg / cm ² or more in the projection region of the gas side electrode to be measured.
In this case, poisonous substances can be efficiently collected in the catalyst layer.

Moreover, it is preferable that content of the said catalyst is 10-500 microgram / cm < ² > (Claim 18).
In this case, it is possible to efficiently collect poisonous substances while ensuring the responsiveness of the gas sensor element.
When the content exceeds 500 μg / cm ² , the gas reaction in the catalyst layer becomes excessive, and the responsiveness may be lowered.

Example 1
A gas sensor element according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, the gas sensor element 1 of this example includes an oxygen ion conductive solid electrolyte body 2, a measured gas side electrode 21 provided on one surface of the solid electrolyte body 2, and a solid electrolyte body 2. A reference gas side electrode 22 formed on the other surface and a heater unit 3 laminated on the solid electrolyte body 2 are provided.

The heater unit 3 is formed by forming a heating element 31 that generates heat upon energization on a heater substrate 32, and the heater substrate 32 is laminated on the solid electrolyte body 2.
As shown in FIGS. 1, 2, 4, and 5, the gas sensor element 1 includes at least a region exposed to the measurement gas in the gas introduction port 11 that introduces the measurement gas to the measurement gas side electrode 21. The surface has a porous protective layer 4 formed so as to cover it.
Further, as shown in FIGS. 1 to 3 and FIG. 5, the protective layer non-forming portion 5 that does not form the porous protective layer 4 is arranged in the lateral direction of the heater substrate 32 in the region corresponding to the axial length of the heating element 31. It is arranged at least at a part of the heating element side corner portion 33 which is a portion.

In this example, as shown in FIGS. 2 to 5, the protective layer non-forming portion 5 is disposed on the entire heating element side corner portion 33, and 60 in the length region exposed to the gas to be measured. % Or more in the side corner portion 330 of the heater substrate 32. Further, as shown in FIG. 2, the protective layer non-forming portion 5 is also disposed at the tip corner portion 34 of the heater substrate 32 at the tip portion of the gas sensor element 1.
The gas sensor element 1 is used in a state where a part of the gas sensor element 1 is inserted into an insulator (see reference numeral 13 in FIG. 9) and sealed with a sealing material. This region is the “region exposed to the gas to be measured”.

The gas sensor element 1 of this example is installed in an exhaust pipe of an internal combustion engine for various vehicles such as an automobile engine, and is an A / F sensor or O ₂ for detecting the oxygen concentration in the exhaust gas for use in an exhaust gas feedback system. It is a sensor.
Further, in the gas sensor element 1, a chamber forming layer 121 is interposed between the solid electrolyte body 2 and the heater unit 3, and the outside air serving as a reference gas is interposed between the chamber forming layer 121 and the solid electrolyte body 2. Is formed. The reference gas side electrode 22 faces the chamber 122.
Further, the side corner portion 330 of the heater substrate 32 has a chamfered portion.

In addition, a porous diffusion resistance layer 124 is laminated on the side where the measured gas side electrode 21 is provided in the solid electrolyte body 2 via a spacer layer 123. A dense shielding layer 125 is laminated on the diffusion resistance layer 124. Further, a measured gas chamber 126 for introducing a measured gas is formed between the solid electrolyte body 2 and the diffusion resistance layer 124, and the measured gas side electrode 21 faces the measured gas chamber 126. is doing.
The portion of the side end face of the diffusion resistance layer 124 that is exposed to the gas to be measured becomes the gas inlet 11. And the corner | angular part of the gas sensor element 1 in the periphery of this gas inlet 11 is formed in the taper shape.

As shown in FIG. 3, the heater unit 3 is provided with a heater pattern 310 in the heater substrate 32 or on the bonding surface with the chamber forming layer 121. The heater pattern 310 is formed in a meandering state near the tip of the heater substrate 32, and this portion becomes the heating element 31. The heater pattern 310 is connected to a heater terminal 311 provided at the proximal end portion of the heater substrate 32.
The solid electrolyte body 2 has zirconia (ZrO ₂ ) as a main component, and the other layers have alumina (Al ₂ O ₃ ) as a main component.

  Further, the diffusion resistance layer 124 and the shielding layer 125 are formed in the vicinity of the distal end portion of the gas sensor element 1, that is, around the detection portion of the gas sensor element 1, and are not provided on the proximal end side. The porous protective layer 4 is provided in the vicinity of the detection portion of the gas sensor element 1. Further, this part is a part exposed to the gas to be measured.

  As shown in FIG. 1 and FIG. 2, the porous protective layer 4 is formed on the side corners 330 and the tip corners 34 of the heater substrate 32, the peripheral portions thereof, and the surface of the heater substrate 32 in the region exposed to the gas to be measured. It is formed in the part except 320. That is, the protective layer non-forming portion 5 is disposed only on the side corner portion 330, the tip corner portion 34, the peripheral portions thereof, and the surface of the heater substrate 3 in the region exposed to the gas to be measured. Conversely, the porous protective layer 4 is also formed on the side surface 100 of the gas sensor element 1 and the surface 129 of the shielding layer 125 in addition to the gas inlet 11.

Specifically, the region where the protective layer non-forming portion 5 is arranged is as follows.
That is, as shown in FIG. 1, the stacking direction distance from the heating element side corner portion 33 (the end portion on the side surface 100 side in the chamfered portion) to the end portion of the protective layer non-forming portion 5 in the side surface 100 of the gas sensor element 1 is a, When the distance in the stacking direction from the heating element side corner portion 33 to the surface of the gas sensor element 1 opposite to the heater portion 31 (the surface 129 of the shielding layer 125) is b, a / b is 0.05 or more.

As shown in FIG. 1, the porous protective layer 4 is formed in two layers, and has a first protective layer 41 close to the surface of the gas sensor element 1 and a second protective layer 42 far from the surface of the gas sensor element 1. . The second protective layer 42 has a larger particle size than the first protective layer 41.
The porous protective layer 4 is mainly composed of γ-alumina or θ-alumina, and the first protective layer 41 of the porous protective layer 4 contains a catalyst made of metal or metal oxide. Become. Thereby, the 1st protective layer 41 functions as a catalyst layer. Here, as the metal catalyst, for example, Pt, Rh, Ru, Pd or the like can be used, and as the metal oxide catalyst, for example, titania (TiO ₂ ) or the like can be used.

  The gas sensor element 1 can also be obtained by separately firing the detection unit having the solid electrolyte body 2 and the heater unit 3 and then bonding or simply contacting them.

Next, an example of a method for forming the porous protective layer 5 will be described with reference to FIGS.
That is, first, as shown in FIG. 7, a mask layer 61 made of an organic material is formed on the heating element side corner portion 33 and its peripheral portion and the surface 320 of the heater substrate 32 (step S1).
Next, as shown in FIG. 8, the porous layer is formed so as to cover the mask layer 61 on the entire surface exposed to the gas to be measured in the length region in which at least the gas introduction port 11 is formed in the gas sensor element 1. A protective layer forming material 40 (slurry) for forming the protective layer 4 is adhered (steps S2 to S5).
Next, by performing a heat treatment, as shown in FIG. 1, the porous protective layer 4 is baked, and the mask layer 61 is burned off to remove the porous protective layer 4 on the mask layer 61, thereby protecting the protective layer. The layer non-formation part 5 is provided (steps S6 and S7).

  Specifically, an acrylic or cellulose binder is dissolved in an organic solvent to form a paste-like mask material 610 at a position where the protective layer non-forming portion 5 in the gas sensor element 1 is to be provided (a heating element side corner portion 33). Etc.) is applied and dried by the pad transfer method to form the mask layer 61 (step S1).

  As shown in FIGS. 9 to 14, the mask layer 61 is formed by transferring a mask material 610 attached to a flexible rubber pad material 62 to the heating element side corner portion 33 or the like. Then, it dries as needed.

Next, the gas sensor element 1 is dipped into the slurry for forming the first protective layer 41 of the porous protective layer 4 and pulled up, so that the gas sensor element 1 has the entire circumference in a predetermined length region. The slurry for 1 protective layer is apply | coated (step S2), and this is dried (step S3).
Next, the slurry for forming the second protective layer 42 is applied by applying the slurry for the second protective layer on the first protective layer 41 by dipping (immersing) the gas sensor element 1 and pulling it up (step). S4), this is dried (step S5).

  Next, the gas sensor element 1 provided with the porous protective layer 4 is fired at about 500 to 1000 ° C. Thereby, the mask layer 61 made of a resin film is thermally decomposed and removed (step S6). The porous protective layer 4 adhered on the mask layer 61 at the time of dipping can have almost no adhesion strength with the gas sensor element 1 and can be easily removed by air blowing, vibration or the like (step S7). . As described above, the porous protective layer 4 can be accurately formed in a desired portion (FIG. 1).

Further, as the mask material 610, for example, an acrylic resin or terpineol as a main component, a slight dispersant, a viscosity stabilizer, and a dye added to ensure the visibility of the coated portion can be used. . As a result, it is possible to facilitate visual inspection of the coating shape or inspection of the coating portion by image recognition using a camera or the like.
Further, as the mask layer 61 (mask material 610), a paste containing an ultraviolet curable resin can also be used. In this case, when the mask layer 61 is formed, the mask layer 610 is cured by pad-transferring the mask material 610 onto a predetermined surface of the gas sensor element 1 and then irradiating ultraviolet rays.

Further, a pad transfer method of the mask material 610 will be described with reference to FIGS.
That is, for the pad transfer, an intaglio 63 provided with a recess 631 having a size, shape and depth corresponding to the mask layer 61 to be obtained, and a ring blade 641 sliding on the upper surface of the intaglio 63 are provided. An ink pot 64 and a pad material 62 are used.
First, as shown in FIG. 9, the concave portion 631 of the intaglio 63 is disposed below the ink pot 64 filled with the mask material 610. As a result, the mask material 610 is filled in the recess 631. In addition, let the position of the intaglio 63 at this time be an origin.

Next, as shown in FIG. 10, by moving the intaglio 63 horizontally, the recess 631 is shifted from below the ink pot 64 and moved below the pad material 62. As a result, the concave portion 631 is filled with a predetermined amount of the mask material 610.
Next, as shown in FIG. 11, the pad material 62 is lowered and brought into close contact with the intaglio 63, and then lifted to transfer the mask material 610 of the recess 631 to the pad material 62.
Next, as shown in FIG. 12, the intaglio 63 is returned to the origin.

Next, as shown in FIG. 13, the mask material 610 is transferred to the gas sensor element 1 by bringing the pad material 62 to which the mask material 610 is adhered into close contact with the gas sensor element 1.
Next, as shown in FIG. 14, the pad material 62 is cleaned with the cleaning tape 65 to remove the residue of the mask material 610.
Then, the same pad transfer process as described above is sequentially performed on the plurality of gas sensor elements 1.
9 to 13, the mask layer 61 is formed in a state where the gas sensor element 1 is inserted and fixed to the insulator 13.

Next, the function and effect of this example will be described.
In the gas sensor element 1, the porous protective layer 5 is formed so as to cover at least a region of the gas inlet 11 exposed to the gas to be measured. As a result, poisonous substances contained in the measurement gas can be removed, and poisoning of the measurement gas side electrode 21 can be prevented.
And the said protective layer non-formation part 4 which does not form the porous protective layer 5 is arrange | positioned in the said heat generating body side corner | angular part 33. FIG. Thereby, a moisture crack can be suppressed effectively.

That is, the mechanism of the effect of suppressing water cracking can be considered as follows.
As described above, the heating element side corner 5 is a portion where thermal stress is particularly likely to be concentrated when exposed to water, and in the gas sensor element 1 of the present invention, porous protection is provided at a portion where the thermal stress is likely to concentrate. A “protective layer non-formation portion 5” that is a portion where the layer 4 is not formed is provided.

  The protective layer non-forming portion 5 does not have water retention, and even if water droplets adhere to the protective layer non-forming portion 5, the water droplets instantaneously leave the element surface due to the above-mentioned Leidenfrost phenomenon, The temperature drop of the part can be suppressed. Therefore, by arranging the protective layer non-forming portion 5 in the heating element side corner portion 33, water cracking can be effectively prevented.

  In the gas sensor element 1, the porous protective layer 4 is not provided on the entire circumference, and it is not particularly necessary to increase the thickness of the porous protective layer 4. Therefore, the heat capacity of the gas sensor element 1 can be kept small, and quick heat performance can be ensured. Thereby, the early activation of the gas sensor element 1 can be ensured.

Moreover, since the said protective layer non-formation part 5 is arrange | positioned in the whole said heat generating body side corner | angular part 33, it can prevent a water-proof crack more reliably. In other words, the heat generating body side corner portion 33 basically tends to cause thermal stress due to water to be concentrated and easily generate cracks. Therefore, by disposing the protective layer non-forming portion 5 over the entire portion, water cracking is further reduced. It can be surely prevented.
Moreover, since the protective layer non-formation part 5 is arrange | positioned in the side corner part 330 of the heater board | substrate 32 in 60% or more of the length area | region exposed to to-be-measured gas, it prevents water | moisture-content cracking more reliably. Can do. That is, there is a possibility that the area exposed to the gas to be measured is exposed to water at any position. And not only the said heat generating body side corner | angular part 33 but the side corner | angular part 330 of the heater board | substrate 32 is a part where stress concentration is easy. Therefore, by arranging the protective layer non-forming portion 5 in the side corner portion 330 of the heater substrate 32 in 60% or more of the length region that is likely to be wetted, it is possible to more effectively prevent water cracking. be able to.

Further, since the protective layer non-forming portion 5 is also disposed at the tip corner portion 34 of the heater substrate 32, it is possible to reliably prevent water cracking at the tip corner portion 34 of the heater substrate 32.
Further, as shown in FIG. 1, the stacking direction distances a and b have a relationship of a / b ≧ 0.05, so that water cracking can be sufficiently prevented. When the a / b is less than 0.05, the porous protective layer 4 is present in a portion close to the heating element side corner portion 33, and water droplets held in the porous protection layer 4 cause the heating element side corner portion 33. There is a risk that thermal stress will be applied to the cracks and cracks will occur. Therefore, by arranging the protective layer non-forming portion 5 in a region from the heating element side corner portion 33 to a position separated by 5% or more of the distance b, a sufficient effect of preventing water cracking can be obtained.

Moreover, since the porous protective layer 4 is mainly composed of γ-alumina or θ-alumina, it can effectively trap poisonous substances in the measurement gas.
Further, even when the porous protective layer 4 contains a catalyst, by using γ-alumina or θ-alumina having a large specific surface area as a main component of the porous protective layer 4, poisoning substances can be trapped effectively. be able to. Further, the heat resistance of the catalyst can be ensured. When the porous protective layer 4 is configured with the same particle diameter and the same thickness when the specific surface area is larger, the distance between the catalysts can be increased and the supporting force can be increased, thereby suppressing the aggregation of the catalyst due to heat. And durability of the catalyst function can be improved.

  Moreover, since the porous protective layer 4 contains the catalyst which consists of a metal or a metal oxide, the poisonous substance in measurement gas can fully be trapped in the porous protective layer 4. And the trapped poisonous substance can be decomposed. In addition, hydrogen gas in the gas to be measured can be burned in the porous protective layer 4, and the detection accuracy of the specific gas concentration by the gas sensor element 1 can be improved.

  The porous protective layer 4 is formed in two layers, and the particle diameter is larger as the layer is farther from the surface of the gas sensor element 1. Thereby, various poisonous substances having different particle sizes can be effectively trapped. That is, by trapping poisonous substances having a large particle diameter in the second protective layer 42 and trapping poisonous substances having a small particle diameter in the first protective layer 41, effective trapping is possible.

  As described above, according to this example, it is possible to provide a gas sensor element that prevents water cracking and ensures early activity.

(Example 2)
In this example, as shown in Tables 1 to 3, the effect of the gas sensor element 1 shown in Example 1 was confirmed.
That is, a test was performed as to how much temperature drop occurs and how much cracking occurs when a water droplet is dropped on the heating element side corner 33 of the gas sensor element 1.
In the test, first, the gas sensor element 1 of Example 1 in which the porous protective layer 4 was not provided in the heating element side corner portion 33 was prepared as Level 1. For comparison, the layers 2, 4, 4, and 5 having the porous protective layer 4 formed at the heating element side corners 33 in thicknesses of 5 μm, 20 μm, 50 μm, and 80 μm were prepared.

For each sample, the results of measuring the temperature drop of the heating element side corner portion 33 when 0.1 μL water droplets and 0.2 μL water droplet are dropped onto the heating element side corner portion 33 corresponding to the center of the heating element 31 are shown. It is shown in 1.
The surface temperature of the gas sensor element in the water droplet dropping part was 700 ° C. The surface temperature was measured with a thermoviewer. Further, the temperature drop ΔT due to the water droplet dropping indicates the minimum value to the maximum value of 10 pieces of measurement data for each level. The thickness of the porous protective layer 4 is the total thickness of the two layers (the first protective layer 41 and the second protective layer 42) in the heating element side corner portion 33. The gas sensor element has a width of 4.5 mm and a thickness of 2.0 mm.

  From Table 1, when the porous protective layer 4 was not formed, the temperature drop amount ΔT was almost the same in both cases of the dropping amount of 0.1 μL and 0.2 μL, and was 30 ° C. to 80 ° C. On the other hand, when the porous protective layer is formed, the amount of temperature decrease ΔT is large, and when the level 2 of 5 μm, the level 3 of 20 μm, and the level 4 of 50 μm are formed, from 135 to 220 ° C. and 100 ° C., respectively. 170 ° C. and 70 to 100 ° C.

In addition, when the porous protective layer was formed to 80 μm as in level 5, the amount of temperature decrease was the same as that in the case where the porous protective layer was not formed (level 1). That is, it is possible to reduce the amount of temperature decrease by forming the porous protective layer thick. However, by increasing the thickness of the porous protective layer, the heat capacity of the gas sensor element 1 increases, the rapid thermal performance decreases, and the so-called active time from when the engine is started until sensor output is obtained becomes longer. As emission regulations become stricter, it is essential to shorten this activation time, in particular, in order to reduce the amount of THC (total hydrocarbon) emitted when starting the engine.
Therefore, in order to prevent moisture cracking while ensuring early activity, it is necessary to employ the gas sensor element of the present invention in which a porous protective layer is not provided at the side portion of the heating element as in Level 1.

  In addition, Table 2 shows the crack occurrence rate in the gas sensor element in the above drop test. The crack occurrence rate is a value calculated by (number of crack occurrences / 10) × 100 in 10 test results for each level.

  As can be seen from Table 2, cracks caused by dropping water droplets do not occur when a level 1 porous protective layer is not formed. The smaller the thickness of the porous protective layer, the higher the occurrence rate of cracks, almost correlating with the magnitude of the temperature drop due to the water droplet dropping shown in Table 1. When the thickness of the porous protective layer is increased to about 80 μm as in Level 5, no cracks are generated. This is presumed that the water absorption phenomenon in the surface direction of the porous protective layer occurred at the same time as the water was applied, and water droplets hardly reached the surface of the device, so that the temperature drop of the device was small and no crack was generated. However, as described above, there is a considerable delay in activation time.

Next, the relationship between the ratio a / b between the stacking direction distances a and b shown in Example 1 (FIG. 1) and the crack generation rate of the gas sensor element due to water droplet dropping was examined.
The results are shown in Table 3. The crack occurrence rate is a value obtained by a calculation method similar to that shown in Table 2 above. The physique of the gas sensor element is the same as that shown in the test method of Table 1 above. The diffusion resistance layer is formed at a position 0.75b away from the side portion of the heating element.

When a / b was 2% (0.02) or less, cracks occurred. At the same time as the Leidenfrost phenomenon, water droplets deposited on the side portions of the heating element spread, and the porous protective layer that is only slightly away from the side portions of the heating element retains a part of the water droplets, resulting in a decrease in the element surface temperature. It is thought that cracks were generated. On the other hand, with respect to those having a / b of 5% or more, since there is little or no influence of water retention of water droplets on the porous protective layer, the temperature drop of the element can be suppressed to a low level due to the Leidenfrost phenomenon, It is thought that no cracks occurred.
From this result, it is considered that water cracking can be more effectively prevented by setting a / b to 5% (0.05) or more.
(Example 3)
This example is an example of the gas sensor element 1 in which the porous protective layer 5 is also formed on the surface of the heater section 3 as shown in FIG.
That is, in the gas sensor element 1 of this example, the porous protective layer 4 is provided on the entire periphery excluding the side corner portion 33 of the heater portion 3 and its peripheral portion. That is, only the side corner portion 33 of the heater portion 3 and its peripheral portion are used as the protective layer non-forming portion 5.

Further, the distance in the width direction from the heating element side corner 33 to the end of the protective layer non-forming part 5 on the surface of the gas sensor element 1 on the heater part 3 side (the surface 320 of the heater substrate 32) is c, and the heater of the gas sensor element 1 When the width of the surface 320 on the part 3 side is d, c / d is 0.02 or more (see Table 4 described later).
Others are the same as in the first embodiment.

Also in the case of this example, since the protective layer non-formation part 5 is arranged in the heating element side corner part 33 where thermal stress tends to concentrate, it is possible to sufficiently prevent water cracking as in the first example. .
In addition, the same effects as those of the first embodiment are obtained.

Next, the relationship between the ratio c / d and the crack generation rate of the gas sensor element due to the water droplet dropping was examined. The test method is the same as that shown in Table 3 in Example 2 above.
The results are shown in Table 4.

As can be seen from Table 4, cracks occurred when c / d was 1% (0.01) or less. On the other hand, when the c / d is 2% (0.02) or more, there is little or no influence of water retention of the water droplets on the porous protective layer. It can be suppressed, and it is considered that cracks did not occur.
From this result, it is considered that water cracking can be more effectively prevented by setting c / d to 2% (0.02) or more.

Example 4
This example is an example of the gas sensor element 1 in which a / b is about 50% as shown in FIG. Others are the same as in the first embodiment.
The side surface 100 of the gas sensor element 1 is more resistant to water than the side portion 33 of the heating element, but a portion where stress is likely to concentrate, such as a minute firing defect, may be the starting point of cracking. In such a case, if the porous protective layer is not formed on the side surface as much as possible, the probability of occurrence of cracks can be suppressed due to the Leidenfrost phenomenon. Therefore, according to this example in which a / b is increased, the crack suppression effect can be improved.
In addition, the same effects as those of the first embodiment are obtained.

(Example 5)
In this example, as shown in FIG. 17, the porous protective layer 4 is not formed on the surface 129 and the corners of the shielding layer 125.
That is, the protective layer non-forming portion 5 that does not form the porous protective layer 4 is the surface opposite to the side where the heater portion 3 is provided in the region corresponding to the axial length of the heating element 31, and the gas inlet port. 11 is arranged in a portion excluding 11.
Others are the same as in the third embodiment.

The surface 129 of the shielding layer 125 is away from the heating element 31 and has a relatively low surface temperature relative to the surface of the heater unit 3. Therefore, even if the porous protective layer 4 is provided on the surface 129 of the shielding layer 125, if the porous protective layer 4 is not provided at the heating element side corner portion 33, the generation of cracks can be suppressed. If the porous protective layer 4 is not formed on the surface 129 of the layer 125, the crack generation rate with respect to the deposited amount of water droplets can be given a margin. In addition, there is an advantage that early activation can be facilitated by reducing the heat capacity of the gas sensor element.
In addition, the same effects as those of the first embodiment are obtained.
The porous protective layer 4 may not be formed on the surface 320 of the heater substrate 32. Alternatively, the porous protective layer 4 may be formed also on the heating element side corner portion 33, and the protective layer non-forming portion 5 may be disposed only on the corner portion with the surface 129.

(Example 6)
In this example, as shown in FIG. 18, the porous protective layer 4 is formed only around the gas inlet 11 of the diffusion resistance layer 124.
Others are the same as in the first embodiment.

In the case of this example, the porous protective layer 4 is provided in the minimum necessary range for trapping poisonous substances, and the area of the protective layer non-forming portion 5 is expanded as much as possible. Therefore, the probability of water cracking can be reduced as much as possible.
Moreover, since the heat capacity of the gas sensor element can be reduced as much as possible, further early activation can be realized.
In addition, the same effects as those of the first embodiment are obtained.

(Example 7)
This example is an example of the gas sensor element 1 in which the porous protective layer 4 is composed of one layer as shown in FIG. Others are the same as those of the first embodiment, and the same effects as those of the first embodiment are obtained.

(Example 8)
This example is an example of the gas sensor element 1 in which the heating element 31 is embedded in a portion close to the chamber 122 as shown in FIG.
Further, the position close to the solid electrolyte body 2 on the side surface 100 of the gas sensor element 1 becomes high because the position of the heating element 31 is close to the solid electrolyte body 2. For this reason, the porous protective layer 4 is not formed on the side surface of the heating element 31.
Others are the same as in the third embodiment.

According to this example, since the heating element 31 is brought close to the solid electrolyte body 2, the activation time of the gas sensor element 1 can be shortened.
In addition, the same effects as those of the third embodiment are obtained.

Example 9
This example is an example of the gas sensor element 1 in which chamfering is not performed on the corners on the shielding layer 125 side and the heater unit 3 side, as shown in FIG.
And the protective layer non-formation part 5 which does not form the porous protective layer 4 is arrange | positioned in the heat generating body side corner | angular part 33 and its peripheral part. Further, the porous protective layer 4 is not provided at the corner portion on the shielding layer 125 side. The porous protective layer 4 is provided on the other surface 129 of the shielding layer 125, the surface 320 of the heater substrate 32, and the side surface 100 of the gas sensor element 1.

Further, in this example, the regions of the protective layer non-forming portion 5 around the heating element side corner portion 33 are a / b = 0.2 (20%) and c / d = 0.1 (10%). This is an important area.
The region of the protective layer non-forming portion 5 around the side corner portion 127 on the shielding layer 125 side is as follows. That is, when the distance in the width direction from the side corner portion 127 to the end portion of the protective layer non-forming portion 5 is e and the width of the gas sensor element 1 is f, e / f is 0.05 (5%). . Further, g / b is 0.1 (10%), where g is the distance in the stacking direction from the side corner portion 127 to the end portion of the protective layer non-forming portion 5.
Others are the same as those of the first embodiment and have the same effects as the first embodiment.

(Example 10)
This example is an example of the gas sensor element 1 having no measured gas chamber (reference numeral 126 in FIG. 1) as shown in FIG. That is, the measured gas side electrode 21 is covered with the diffusion resistance layer 124 in contact with the measured gas side electrode 21.
Others are the same as those of the first embodiment and have the same effects as the first embodiment.

(Example 11)
As shown in FIG. 23, this example is an example of the gas sensor element 1 configured to allow gas diffusion rate control to function in the pinhole 142.
In the gas sensor element 1 of this example, a dense layer 141 is laminated on the measured gas chamber 126 side of the solid electrolyte body 2 via a spacer layer 123, and a pinhole 142 is formed in the dense layer 141. The pinhole 142 is covered with a porous layer 143 laminated on the dense layer 141.

As a result, the measurement gas is introduced into the measurement gas chamber 126 through the pinhole 142, and the diffusion-controlled rate of the measurement gas can be adjusted according to the size and number of the pinholes 142.
The porous protective layer 4 is provided on the surface 144 of the porous layer 143, the surface 320 of the heater substrate 32, and the side surface 100 of the gas sensor element 1. In addition, a protective layer non-forming portion 5 that does not form the porous protective layer 4 is disposed in the heat generating body side corner portion 33 and the side corner portion 145 of the porous layer 143.
Others are the same as those of the first embodiment, and the same effects as those of the first embodiment can be obtained.

  The gas sensor element of the present invention is not limited to the shape shown in each of the above embodiments. For example, in the gas sensor element shown in Embodiment 1, the heating element side corner portion 33 is not chamfered, and the shielding layer 125 side is formed. The corners of the surface can be applied even in a chamfered state, and the present invention can be applied to gas sensor elements having various shapes.

It is sectional drawing of the gas sensor element in Example 1, Comprising: It is AA arrow sectional drawing (up-down direction is reverse) of FIG. 1 is a perspective view of a gas sensor element in Embodiment 1. FIG. FIG. 3 is an explanatory plan view of the gas sensor element showing the position of the heating element in the first embodiment. FIG. 3 is a plan view of a gas sensor element in the first embodiment. The side view of the gas sensor element in Example 1. FIG. FIG. 3 is a process flow diagram showing a method for forming a porous protective layer in Example 1. Sectional explanatory drawing which shows the state in which the mask layer was formed in the predetermined position of the gas sensor element in Example 1. FIG. Sectional explanatory drawing which shows the state which formed the slurry of the porous protective layer in the perimeter of the gas sensor element from the mask layer in Example 1. FIG. FIG. 3 is a first explanatory diagram showing a pad transfer method of a mask layer in Example 1. FIG. 6 is a second explanatory diagram showing a pad transfer method of a mask layer in Example 1. FIG. 4 is a third explanatory diagram showing a pad transfer method of a mask layer in Example 1. FIG. 6 is a fourth explanatory diagram showing a pad transfer method of a mask layer in Example 1. FIG. 10 is a fifth explanatory diagram illustrating a pad transfer method for a mask layer in the first embodiment. FIG. 6 is a sixth explanatory diagram illustrating a pad transfer method of a mask layer in the first embodiment. Sectional drawing of the gas sensor element in Example 3. FIG. Sectional drawing of the gas sensor element in Example 4. FIG. Sectional drawing of the gas sensor element in Example 5. FIG. Sectional drawing of the gas sensor element in Example 6. FIG. Sectional drawing of the gas sensor element in Example 7. FIG. Sectional drawing of the gas sensor element in Example 8. FIG. Sectional drawing of the gas sensor element in Example 9. FIG. Sectional drawing of the gas sensor element in Example 10. FIG. Sectional drawing of the gas sensor element in Example 11. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas sensor element 11 Gas inlet 2 Solid electrolyte body 21 Gas side electrode 22 to be measured 22 Reference gas side electrode 3 Heater part 31 Heating body 32 Heater board 33 Heating body side corner part 4 Porous protective layer 5 Protection layer non-formation part

Claims (18)

An oxygen ion conductive solid electrolyte body, a gas side electrode to be measured provided on one side of the solid electrolyte body, a reference gas side electrode formed on the other side of the solid electrolyte body, and the solid electrolyte body A gas sensor element having a laminated heater portion,
The heater portion is formed by forming a heating element that generates heat upon energization on the heater substrate, and the heater substrate is laminated on the solid electrolyte body.
The gas sensor element has a porous protective layer formed on the surface so as to cover at least a region exposed to the gas to be measured among gas inlets for introducing the gas to be measured to the gas to be measured side electrode. ,
In addition, a protective layer non-forming portion that does not form the porous protective layer is disposed on at least a part of a side portion of the heating element that is a side corner portion of the heater substrate in a region corresponding to the axial length of the heating element. A gas sensor element characterized by comprising: An oxygen ion conductive solid electrolyte body, a gas side electrode to be measured provided on one side of the solid electrolyte body, a reference gas side electrode formed on the other side of the solid electrolyte body, and the solid electrolyte body A gas sensor element having a laminated heater portion,
The heater portion is formed by forming a heating element that generates heat upon energization on the heater substrate, and the heater substrate is laminated on the solid electrolyte body.
The gas sensor element has a porous protective layer formed on the surface so as to cover at least a region exposed to the gas to be measured among gas inlets for introducing the gas to be measured to the gas to be measured side electrode. ,
Further, the protective layer non-forming portion that does not form the porous protective layer is a surface opposite to the side where the heater portion is provided in a region corresponding to the axial length of the heating element, and the gas introduction port A gas sensor element, wherein the gas sensor element is disposed in at least a part of a portion excluding.   In Claim 2, the said protective layer non-formation part is arrange | positioned also in the at least one part of the heat generating body side corner part which is a side corner part of the said heater board | substrate in the area | region corresponding to the axial direction length of the said heat generating body. A gas sensor element characterized by the above.   4. The gas sensor element according to claim 1, wherein the protective layer non-forming portion is disposed on the entire side of the heating element.   5. The gas sensor element according to claim 12, wherein the protective layer non-forming portion is disposed in a side corner portion of the heater substrate in 60% or more of a length region exposed to the gas to be measured. .   6. The gas sensor element according to claim 12, wherein the protective layer non-forming portion is also arranged at a tip corner portion of the heater substrate at a tip portion of the gas sensor element.   7. The distance in the stacking direction from the heating element side corner to the end of the protective layer non-forming portion on the side surface of the gas sensor element is defined as a, and the heating element side corner to the gas sensor element according to claim 12. A gas sensor element, wherein a / b is 0.05 or more, where b is the distance in the stacking direction to the surface on the opposite side of the heater part.   The width direction distance from the said heat generating body side corner part to the edge part of the said protective layer non-formation part in the surface of the said heater part side of the said gas sensor element is set to c, The gas sensor element of any one of Claims 12-7 The gas sensor element, wherein c / d is 0.02 or more, where d is the width of the surface on the heater portion side.   9. The gas sensor element according to claim 1, wherein the porous protective layer contains γ-alumina, θ-alumina, or titania as a main component.   The gas sensor element according to any one of claims 1 to 9, wherein the porous protective layer is formed in a plurality of layers, and the particle diameter is larger as the layer is farther from the surface of the gas sensor element.   In Claim 10, the said porous protective layer consists of two layers, the particle size of the inner side 1st protective layer is smaller than the outer side 2nd protective layer, and the average particle diameter of the said 1st protective layer is 1 The gas sensor element according to claim 1, wherein the second protective layer has an average particle diameter of 2 to 100 µm.   12. The gas sensor element according to claim 1, wherein at least one of the porous protective layers is a catalyst layer containing a catalyst made of a noble metal or a metal oxide.   13. The gas sensor element according to claim 12, wherein the catalyst is made of one or more kinds of precious metals of Pt, Rh, Pd, and Ru.   14. The gas sensor element according to claim 12, wherein the catalyst is made of a noble metal having an average particle diameter of 0.01 to 5 [mu] m.   The gas sensor element according to claim 14, wherein the catalyst is made of a noble metal having an average particle diameter of 0.1 to 2 μm.   The gas sensor element according to claim 12, wherein the catalyst includes at least titania. 17. The gas sensor element according to claim 12, wherein the catalyst layer has a catalyst content of 10 μg / cm ² or more in a projection region of the gas side electrode to be measured. The gas sensor element according to claim 17, wherein the content of the catalyst is 10 to 500 µg / cm ² .

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