JP2009080099A - Gas sensor element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor element reconciling securement of water resistance with suppression of delay of a sensor active period, and also to provide its manufacturing method. <P>SOLUTION: The gas sensor element 2 is formed by stacking a sensor substrate where a pair of electrodes are disposed on both surfaces of a solid electrolyte, and a heater substrate 4 where a heating element 42 is disposed in a ceramic object 41. The heating element 42 has: a heating section 401 formed by meandering a conductor; and a lead section 402 formed of the conductor pulled out of both ends of the heating section 401. The gas sensor element 2 has, on one side L1 of the longitudinal direction L, a heating region where the heating section 401 faces the sensor substrate, and the whole heating region is covered with a porous protective layer 5 having many pores of ceramic particles. The other side end P1 of the longitudinal direction L in the porous protective layer 5 projects from the other side end P2 of the longitudinal direction L in the heating section 401 toward the other side L2 of the longitudinal direction L within a range of 3 mm towards other side L2 of longitudinal direction L. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a gas sensor element for detecting the concentration of a specific gas component such as oxygen, nitrogen oxide, and hydrocarbon, and a method for manufacturing the same.

For example, in a gas sensor element that detects an air-fuel ratio of an engine or the like based on a difference in oxygen concentration between a reference gas such as the atmosphere and a measured gas such as exhaust gas, the surface of the diffusion resistance layer into which the measured gas is introduced, etc. A trap layer is formed to trap poisonous substances in the measurement gas.
Further, for example, in the laminated gas sensor element of Patent Document 1, it is disclosed that the corner of the element body is covered with a porous protective layer, and the thickness of the porous protective layer is 20 μm or more from the corner. Further, for example, in the gas sensor element and the manufacturing method thereof in Patent Document 2, the gas sensor element is immersed in a slurry made of ceramic powder, dried and baked to form a poisoning prevention layer on the surface of the gas sensor element. Yes. Further, it is disclosed that the poisoning prevention layer is formed in an elliptical shape in the cross section of the gas sensor element.

  The laminated gas sensor element includes a sensor substrate in which a pair of electrodes is provided on a solid electrolyte body, and a heater substrate for quickly bringing the sensor substrate to an activation temperature. In the gas sensor element, if moisture adheres to (is exposed to water) the heating area of the heater substrate, the gas sensor element may be broken by thermal shock. Therefore, it is conceivable that the entire heating region in the gas sensor element is covered with the trap layer (porous protective layer, poisoning prevention layer) in order to improve the water covering strength, which is the strength against element cracking due to the water.

JP 2006-171013 A JP 2006-250537 A

However, if the trap layer covers the portion away from the heating region, the heat mass (heat capacity) of the trap layer increases, and the sensor activation time, which is the time for bringing the gas sensor element to the activation temperature by the heater substrate, is long. turn into.
Conventionally, since the trap layer formation range was not particularly controlled, a large trap layer may be formed in a portion other than the heating region, and a gas sensor element having a short sensor activation time can be stably obtained. Was difficult.

  Therefore, the inventors investigated the relationship between the formation range of the trap layer with respect to the heating region and the sensor activation time, and as described later, with respect to the other end of the heating region provided on one side in the longitudinal direction of the gas sensor element, It was found that if the protruding amount at the other end of the trap layer (porous protective layer) formation region is 3 mm or less, the delay of the sensor activation time can be sufficiently suppressed. That is, it was found that if the protrusion amount exceeds 3 mm, the sensor activation time may be greatly delayed.

  The present invention has been made in view of such a conventional problem, and intends to provide a gas sensor element capable of achieving both ensuring of moisture resistance and suppression of delay in sensor activation time, and a method for manufacturing the same. It is.

A first invention is a heater substrate in which a sensor substrate in which a pair of electrodes are provided on both surfaces of a solid electrolyte body having oxygen ion conductivity, and a heating element that generates heat by energizing a ceramic body in electrical insulation. In the gas sensor element formed by laminating
The heating element has a heating part formed by meandering a conductor, and a lead part by a conductor drawn from both ends of the conductor forming the heating part,
The gas sensor element has, on one side in the longitudinal direction, a heating region where the heat generating portion and the sensor substrate are opposed to each other, and the entire heating region is formed with a large number of pores made of ceramic particles. Covered with a porous protective layer,
The other end in the longitudinal direction of the porous protective layer protrudes from the other end in the longitudinal direction of the heat generating portion within a range of 3 mm toward the other side in the longitudinal direction. (Claim 1).

  The gas sensor element of the present invention is formed by covering the entire heating region located on one side in the longitudinal direction with the porous protective layer. With this porous protective layer, it is possible to trap (capture) poisonous substances in the gas to be measured, to guide the gas to be measured to one of the electrodes in the solid electrolyte body, and for the heated gas sensor element to It can prevent that it breaks with water.

In the gas sensor element of the present invention, the other end in the longitudinal direction of the porous protective layer protrudes from the other end in the longitudinal direction of the heat generating portion (heating region) within a range of 3 mm toward the other side in the longitudinal direction. ing. Thereby, the heat mass (heat capacity) of the porous protective layer increases, and it can be suppressed that the sensor activation time (time for bringing the gas sensor element to the activation temperature by the heater substrate) becomes long.
The amount of the other end in the longitudinal direction of the porous protective layer protruding from the other end in the longitudinal direction of the heat generating portion (heating region) toward the other side in the longitudinal direction can be 0 mm (porous protection) (The other end in the longitudinal direction of the layer and the other end in the longitudinal direction of the heat generating portion (heating region) can be substantially aligned in the longitudinal direction.)

  Therefore, according to the gas sensor element of the present invention, it is possible to achieve both of ensuring the moisture intensity and suppressing the delay of the sensor activation time.

According to a second aspect of the present invention, in the method for manufacturing the gas sensor element,
After the immersion process of immersing the gas sensor element in the ceramic material containing the ceramic particles in a solvent and the drying process of drying the ceramic material adhered to the surface of the gas sensor element, heat treatment is performed after repeating 2 to 5 times. And forming the porous protective layer. (Claim 4)

The method for producing a gas sensor element of the present invention is a method by which the gas sensor element having the above-described excellent properties can be efficiently produced without causing a crack or the like in the porous protective layer.
In the manufacturing method of this invention, the film thickness of the ceramic material made to adhere to the surface of a gas sensor element by one immersion can be suppressed appropriately by repeating the said immersion process and a drying process 2-5 times. Thereby, generation | occurrence | production of the crack etc. which arises when the film thickness of ceramic material is large can be suppressed effectively.

  Therefore, according to the method for producing a gas sensor element of the present invention, it is possible to efficiently produce a gas sensor element capable of ensuring both the strength of water exposure and suppressing the delay of the sensor activation time.

A preferred embodiment of the gas sensor element and the manufacturing method thereof according to the first and second inventions described above will be described.
1st, 2nd invention WHEREIN: The quantity which the other end of the longitudinal direction in the said porous protective layer protrudes toward the other side of a longitudinal direction from the other end of the longitudinal direction in the said heat generating part (heating area) is 0 mm If it is less than that, that is, if the porous protective layer does not cover the entire heating region, it is not possible to ensure sufficient water resistance, and there is a risk of water cracking in the gas sensor element. In addition, since it is difficult on a manufacturing method to make the protrusion amount of the said porous protective layer into 0 mm, this protrusion amount can be 1 mm or more, for example.
On the other hand, if the amount of the other end in the longitudinal direction of the porous protective layer protruding from the other end in the longitudinal direction of the heat generating portion (heating region) toward the other side in the longitudinal direction exceeds 3 mm, the porous protection layer There is a possibility that the heat mass (heat capacity) of the layer increases and the sensor activation time becomes long.

Further, the protruding portion in which the porous protective layer protrudes from the other end in the longitudinal direction in the heat generating portion to the other side in the longitudinal direction is the thinnest portion in the cross section orthogonal to the longitudinal direction. It is preferable that the range of 80 to 95% has a thickness of 30 μm or more.
In this case, a porous protective layer having an appropriate thickness can be formed in an appropriate range on one side in the longitudinal direction of the gas sensor element.
In addition, when the range which formed the porous protective layer which has a thickness of 30 micrometers or more is less than 80% of the length of the said protrusion part, there exists a possibility that the waterproof strength by a porous protective layer may fall. On the other hand, when the range in which the porous protective layer having a thickness of 30 μm or more is formed exceeds 95% of the length of the protruding portion, the other end in the longitudinal direction of the porous protective layer is inclined or It becomes difficult to form a step.
Moreover, the thickness of the said porous protective layer can be 700 micrometers or less at the maximum part, for example.

In addition, the porous protective layer is preferably formed such that an end portion on the other side in the longitudinal direction has an inclined shape or a step shape in which the thickness decreases toward the other side in the longitudinal direction. ).
In this case, in the gas sensor element, it is possible to suppress an abrupt change in thickness at the boundary portion between the covering portion and the non-covering portion due to the porous protective layer, and to reduce thermal stress.
Note that the inclined end portion may be inclined linearly or may be inclined convexly.

Hereinafter, embodiments of the gas sensor element and the manufacturing method thereof according to the present invention will be described with reference to the drawings.
(Example 1)
As shown in FIG. 2, the gas sensor element 2 of this example includes a sensor substrate 3 provided with a pair of electrodes 32A and 32B on both surfaces of a solid electrolyte body 31 having oxygen ion conductivity, and a ceramic body having electrical insulation. 41 is laminated with a heater substrate 4 provided with a heating element 42 that generates heat when energized.

As shown in FIGS. 3 and 4, the heating element 42 has a heat generating portion 401 formed by meandering conductors, and a lead portion 402 made of a conductor drawn from both ends of the heat generating portion 401. The gas sensor element 2 has a heating region where the heat generating portion 401 and the sensor substrate 3 face each other on one side L1 in the longitudinal direction L. The entire heating region has a large number of pores made of ceramic particles. It covers with the porous protective layer 5 which becomes. The other end P1 in the longitudinal direction L of the porous protective layer 5 projects from the other end P2 in the longitudinal direction L of the heat generating portion 401 toward the other side L2 in the longitudinal direction L within a range of 3 mm. In the figure, the protrusion amount of the porous protective layer 5 is indicated by A.
2 shows a cross section perpendicular to the longitudinal direction L of the gas sensor element 2, and FIG. 4 shows a partial cross section of the gas sensor element 2 in the longitudinal direction L.

Hereinafter, the gas sensor element 2 of this example and the manufacturing method thereof will be described in detail with reference to FIGS.
As shown in FIG. 2, the gas sensor 1 of this example is a vehicle-mounted limiting current type gas sensor, and measures the oxygen concentration in the exhaust gas as the gas to be measured. In addition, the gas sensor 1 of this example applies a voltage that generates a limiting current characteristic between a pair of electrodes 32A and 32B provided on both surfaces of the solid electrolyte body 31, and the measured gas side electrode 32A that is one of the electrodes. A current generated between the pair of electrodes 32A and 32B is detected according to the difference in oxygen concentration between the gas to be measured and the reference gas (the atmosphere, etc.) that is in contact with the reference gas side electrode 32B that is the other electrode. The air-fuel ratio in the engine can be obtained.
Further, the sensor substrate 3 of the gas sensor element 2 of the present example has a function of a pumping cell that adjusts the oxygen concentration in the gas to be measured by a pair of electrodes 32A and 32B provided on both surfaces of the solid electrolyte body 31, and the measurement target. It has a one-cell structure that combines the function of a sensing cell that measures the oxygen concentration in the gas.

As shown in the figure, a diffusion resistance layer 33 for diffusing the measurement gas and controlling the flow thereof is laminated on the surface of the solid electrolyte body 31 provided with the measurement gas side electrode 32A. A shielding layer 34 is laminated on the surface of the diffusion resistance layer 33. The diffusion resistance layer 33 and the shielding layer 34 can be formed of alumina or the like. The pair of electrodes 32A and B can be formed of platinum or the like.
The porous protective layer 5 is configured to trap poisonous substances in the measurement gas guided to the diffusion resistance layer 33 and to protect the gas sensor element 2 from moisture.

As shown in FIG. 2, the heater substrate 4 is laminated on the surface of the solid electrolyte body 31 provided with the reference gas side electrode 32B. The heater substrate 4 is formed by sandwiching a heating element 42 between one ceramic body 41A for forming the reference gas chamber 45 around the reference gas side electrode 32B and the other ceramic body 41B. The heating element 42 is formed by pattern-printing a conductor made of platinum or the like on any ceramic body 41.
As shown in FIG. 4, the pair of electrodes 32 </ b> A, B in the solid electrolyte body 31 is formed at a position facing the heat generating portion 401 (heating region) by the heat generating body 42.

As shown in FIG. 3, in the heater substrate 4, the heat generating portion 401 by the heating element 42 can be formed by meandering in the longitudinal direction L of the gas sensor element 2, and as shown in FIG. 5, the lateral direction W of the gas sensor element 2. It can also be formed by meandering in the direction perpendicular to the longitudinal direction L.
In the gas sensor element 2, a heating region where the heat generating portion 401 and the sensor substrate 3 in the heater substrate 4 face each other and a current-carrying region where the lead portion 402 and the sensor substrate 3 in the heater substrate 4 face each other are formed. .

As shown in FIG. 1, the rear end side portion (the portion on the other end side L <b> 2) 202 of the gas sensor element 2 is fixed to the metal housing 11 via the insulator portion 14 having electrical insulation, and the gas sensor element 2. The tip end portion (portion on one end side L1) 201 is covered with an element cover 12 fixed to the tip end portion of the housing 11. The element cover 12 includes an inner cover 12A that covers the distal end portion 201 of the gas sensor element 2, and an outer cover 12B that covers the inner cover 12A. In the inner cover 12A and the outer cover 12B, measured gas inlets 13A, B are formed at different positions in the longitudinal direction L.
Connected to the rear end portion 202 of the gas sensor element 2 are a conductive fitting 15 and a lead wire 16 for electrically connecting the pair of electrodes 32A, 32B to the outside of the gas sensor 1.

As shown in FIG. 2, the gas sensor element 2 of the present example has a shape in which a C surface is formed at four corners of a quadrangular shape in a cross section orthogonal to the longitudinal direction L. On both sides of the layer 33, notched surfaces (C surfaces) 36 for guiding the gas to be measured to the diffusion resistance layer 33 are formed.
The cross-sectional shape of the gas sensor element 2 has a substantially rectangular shape that is thin in the stacking direction D of the sensor substrate 3 and the heater substrate 4.

  Further, as shown in FIG. 4, the end 51 on the other side L2 in the longitudinal direction L of the porous protective layer 5 is formed in an inclined shape whose thickness decreases toward the other side L2 in the longitudinal direction L. . The inclined end portion 51 may be inclined not only linearly but also in a convex shape. By making the end portion 51 on the other side L2 in the longitudinal direction L of the porous protective layer 5 into an inclined shape, in the gas sensor element 2, a sharp portion is formed at the boundary portion between the covered portion and the non-covered portion by the porous protective layer 5. It is possible to suppress a change in thickness and to reduce thermal stress.

  As shown in FIG. 6, the end portion 51 on the other side L2 in the longitudinal direction L of the porous protective layer 5 can be formed in a stepped shape whose thickness decreases toward the other side L2 in the longitudinal direction L. As shown in Example 2, which will be described later, the stepped end 51 includes a lower porous protective layer 5A made of lower ceramic particles having a small particle size and an upper ceramic having a larger particle size than the lower ceramic particles. The upper porous protective layer 5B made of particles (two layers in FIG. 6) can be formed by separate immersion (dipping).

  As shown in FIG. 2, the porous protective layer 5 has the largest thickness in the central portion of the surface in the stacking direction D of the sensor substrate 3 and the heater substrate 4 in the cross section perpendicular to the longitudinal direction L. The thickness at all corners is the thinnest. And the porous protective layer 5 has the thickness of 30 micrometers or more in the thinnest corner | angular part.

Further, the protruding portion 52 in which the porous protective layer 5 protrudes from the other end P2 in the longitudinal direction to the other side in the longitudinal direction in the heat generating portion 401 is the thinnest portion in the cross section orthogonal to the longitudinal direction, that is, the corner portion. A range of 80 to 95% in the longitudinal direction has a thickness of 30 μm or more. The inclined end portion 51 is formed in the remaining range in the longitudinal direction L of the porous protective layer 5.
Further, the porous protective layer 5 of this example is formed by forming a large number of pores with alumina particles as ceramic particles. And the porosity per unit volume of the porous protective layer 5 is 20% or more.

In addition, on the surface of the gas sensor element 2 (each surface of the sensor substrate 3, the heater substrate 4, the shielding layer 34, etc.), an underlayer formed by forming a large number of pores with ceramic particles can be formed. This underlayer can be formed by firing at the same time as the gas sensor element 2.
The porous protective layer 5 of this example is formed by laminating ceramic particles having electrical insulation properties in a plurality of layers (two layers in this example) in order to improve trapping performance of a plurality of types of poisons. The average particle size of the upper ceramic particles is larger than the average particle size of the lower ceramic particles.

  The gas sensor element 2 of this example is formed by firing in a state where the sensor substrate 3, the heater substrate 4, the diffusion resistance layer 33, and the shielding layer 34 are laminated. And the porous protective layer 5 immerses the gas sensor element 2 in a slurry-like ceramic material containing a large number of ceramic particles in water as a solvent, and attaches the ceramic material to the surface of the gas sensor element 2. After drying, heat treatment is performed.

  The gas sensor element 2 of this example is formed by covering the entire heating region located on one side L <b> 1 in the longitudinal direction L with a porous protective layer 5. The porous protective layer 5 can trap the poisoning substance in the measurement gas, guide the measurement gas to the measurement gas side electrode 32A in the solid electrolyte body 31, and is heated. It is possible to prevent the gas sensor element 2 from being broken by water.

Further, in the gas sensor element 2 of the present example, the other end P1 in the longitudinal direction L of the porous protective layer 5 extends from the other end P2 in the longitudinal direction L of the heat generating portion 401 (heating region) to the other side L2 in the longitudinal direction L. It projects in the range of 3 mm toward Thereby, the heat mass (heat capacity) of the porous protective layer 5 increases, and it can be suppressed that the sensor activation time (the time for bringing the gas sensor element 2 to the activation temperature by the heater substrate 4) becomes long. .
Therefore, according to the gas sensor element 2 of the present example, it is possible to satisfy both of ensuring the moisture intensity and suppressing the delay of the sensor activation time.

  FIG. 7 shows the amount of protrusion of the porous protective layer 5 on the horizontal axis (the distance from the other end P2 in the longitudinal direction L of the heat generating portion 401 to the other end P1 in the longitudinal direction L of the porous protective layer 5) A (mm) Is a graph showing the relationship between the two, taking the rate of occurrence of water cracking (%) on the vertical axis.

Here, the incidence (%) of water cracking was evaluated as follows.
That is, it is confirmed whether or not an element crack occurs when a water droplet is dropped on the surface of the sensor element 2 at the position of the other end P2 of the heat generating part 401 in a state where the gas sensor element 2 is heated to 700 ° C. The amount of the water droplet is such an amount that the element cracking is surely generated when it is dropped on the surface of the gas sensor element having no porous protective layer. Then, this test was performed on 100 samples per level, and by examining how many samples caused element cracking (water cracking), the incidence of water cracking was calculated.

  About the presence or absence of an element crack, a part of gas sensor element after said dripping test is immersed in an ethanol bath. At this time, a part of one side L1 in the longitudinal direction of the gas sensor element 2 including the heating region is made to exist below the liquid surface of the ethanol bath. The insulation resistance was measured by applying a voltage between the heating element of the gas sensor element 2 and the ethanol bath and between the reference gas side electrode 32B and the ethanol bath. The presence or absence of moisture cracking was confirmed depending on whether or not the insulation resistance value measured at this time was greatly reduced.

In addition, as shown in Table 1, the protrusion amount A is set for each of the three types of gas sensor elements 2 having different cross-sectional areas perpendicular to the longitudinal direction in the heating region of the gas sensor element 2 and the length of the heating region. Evaluation was performed using a sample that was changed between −2 mm and +4 mm. Here, the sectional area of the porous protective layer 5 is not included in the sectional area. The protrusion amount A of −2 mm represents a state in which the other end P1 of the porous protective layer 5 is retracted to the one side L1 from the other end P2 of the heat generating portion 401.
Further, the adjustment of the protrusion amount A is as described in the method for manufacturing a gas sensor element shown in Example 2 described later.

The evaluation results are shown in FIG. In FIG. 7, a plot T1 represents data for the gas sensor element 2 having a cross-sectional area of 9 mm ² and a heating area length of 6.2 mm, and a plot T2 is a gas sensor having a cross-sectional area of 6.84 mm ² and a heating area length of 8.5 mm. Data for element 2 is represented, and plot T3 represents data for gas sensor element 2 having a cross-sectional area of 4.48 mm ² and a heating region length of 8.5 mm. The same applies to plots T1, T2, and T3 in FIG.

8 shows the amount of protrusion of the porous protective layer 5 (distance from the other end P2 in the longitudinal direction L of the heat generating portion 401 to the other end P1 of the porous protective layer 5 in the longitudinal direction L) A ( mm), and the vertical axis represents the rate of decrease (%) in sensor activation time, showing the relationship between the two.
The decrease rate (%) of the sensor active time is a value represented by a ratio (%) to the sensor active time when the protrusion amount A of the porous protective layer 5 is 0 mm.
The sensor activation time is a value obtained by measuring the time taken for the surface of the gas sensor element 2 to rise from room temperature to 700 ° C. when the heating element 42 is energized.

  Also for the evaluation of the rate of decrease of the sensor activation time, for the three types of gas sensor elements 2 having different cross-sectional areas and heating region lengths, samples in which the protrusion amount A was changed between −2 mm and +4 mm were used. And evaluated. Further, the number of samples at each level was 10, and the average value was calculated and shown in FIG.

As shown in FIG. 8, as the protrusion amount A of the porous protective layer 5 increases, the rate of decrease in sensor active time increases (the sensor active time increases), whereas as shown in FIG. It can be seen that when the protruding amount A of the quality protective layer 5 is less than 0 mm, water cracking occurs, that is, the water receiving strength decreases. It can also be seen that when the protruding amount A of the porous protective layer 5 exceeds 3 mm, the sensor activation time is significantly reduced.
It can also be seen that this tendency is common to a plurality of types of gas sensor elements 2 having different values without depending on the cross-sectional area of the gas sensor element 2 and the length of the heating region.
From this result, it can be seen that by setting the protrusion amount A of the porous protective layer 5 within the range of 0 to 3 mm, it is possible to satisfy both of ensuring the moisture resistance and suppressing the delay of the sensor activation time.

(Example 2)
This example is an example showing a method suitable for manufacturing the gas sensor element 2 shown in the first embodiment.
Specifically, in this example, after the following dipping process and drying process are repeatedly performed, a heat treatment process is performed to form the porous protective layer 5 on the surface of the gas sensor element 2.
In the dipping process, the tip side portion 201 (the portion where the heating region is formed) in the longitudinal direction L of the gas sensor element 2 is dipped in a ceramic material containing ceramic particles in water as a solvent. Then, the gas sensor element 2 is pulled up from the slurry-like ceramic material, and the ceramic material is attached to the surface of the tip side portion 201. In the state where the gas sensor element 2 is mounted on the insulator, the tip end portion 201 protruding from the insulator is immersed in the slurry-like ceramic material.

  In the drying step, the ceramic material adhered to the gas sensor element 2 is dried. In the drying process of this example, heated air is blown to dry. In the drying step, the ceramic material attached to the gas sensor element 2 is dried until the moisture content becomes 20 wt% or less.

In this example, as a dipping process, a first ceramic material having a particle size of ceramic particles of 10 μm or less is attached to the surface of the gas sensor element 2 and a drying process is performed. Next, a second ceramic material having a particle size of ceramic particles larger than that of the first ceramic material is adhered on the first ceramic material, and a drying process is performed. Next, a third layer ceramic material having a particle size of ceramic particles equivalent to that of the second layer ceramic material is adhered, and a drying process is performed.
Thus, in this example, the lower porous protective layer 5A having a thin film thickness is formed by the first ceramic material, and the upper porous protective layer having a thick film thickness by the second and third ceramic materials. 5B is formed (see FIG. 6).

In addition, after repeatedly performing the dipping process and the drying process, as the main drying process, the ceramic material on the surface of the gas sensor element 2 is dried until the water content becomes approximately 0 wt%.
Thereafter, in the heat treatment step, the ceramic material (ceramic particles) dried almost completely is heat treated to form the porous protective layer 5 on the surface of the gas sensor element 2.
In addition, the base layer which baked simultaneously with the gas sensor element 2 can be provided in the surface of the gas sensor element 2 before performing an immersion process.

  In addition, adjustment of protrusion amount A is performed by controlling the immersion height of the gas sensor element 2 to the slurry-like ceramic material in an immersion process. That is, since the formation position of the heating region (heat generating portion 401) in the gas sensor element 2 is known from the design value, for example, the length from the end on one side L1 of the gas sensor element 2 to the other end P1 of the heating region is also known. ing. Therefore, the porous protective layer 5 can be formed so as to have the respective predetermined protruding amounts A by immersing in a slurry-like ceramic material from the end of the one side L1 of the gas sensor element 2 to a predetermined amount of height. it can.

In the manufacturing method of this example, the film thickness of the ceramic material to be attached to the surface of the gas sensor element 2 by one dipping is appropriately determined by repeating the dipping process and the drying process of the second and subsequent ceramic materials twice. Can be suppressed. Thereby, generation | occurrence | production of the crack etc. which arises when the film thickness of ceramic material is large can be suppressed effectively.
In addition, the immersion process and drying process of the ceramic material after the second layer can be repeated 2 to 5 times.

Therefore, according to the method of manufacturing the gas sensor element 2 of the present example, the gas protective element 2 that can ensure both the strength of moisture and the suppression of the delay of the sensor activation time is cracked in the porous protective layer 5. Can be produced efficiently without causing any problems.
Also in this example, the configuration of the gas sensor element 2 is the same as that of the first embodiment, and the same effects as those of the first embodiment can be obtained.

Example 3
In this example, as shown in FIGS. 9 and 10, the protrusion 52 having the porous protective layer 5 protruding from the other end P <b> 2 in the longitudinal direction to the other side L <b> 2 in the longitudinal direction of the heat generating portion 401 has a predetermined thickness t or more. It is the example which investigated the relationship between the ratio of the longitudinal direction range M, and a moisture cracking incidence.
Here, the predetermined thickness t of the porous protective layer 5 is a thickness measured at the thinnest portion in the cross section orthogonal to the longitudinal direction, that is, at the corner of the gas sensor element 2.

  As shown in Table 2 and FIG. 9, first, in the gas sensor element 2 in which the predetermined thickness t is 15 μm, a region in which the longitudinal direction range M of the protrusion 52 is equal to or greater than the predetermined thickness t (15 μm) Five types of samples varied in the above were prepared. Similarly, for the gas sensor element 2 having the predetermined thickness t of 30 μm and the gas sensor element 2 having the predetermined thickness t of 45 μm, five types of samples were respectively produced.

The predetermined thickness t was adjusted by changing the number of times the gas sensor element 2 was immersed in the ceramic material shown in Example 2. That is, for a sample having a predetermined thickness t of 15 μm, as shown in FIG. 9A, the number of immersions is set to two to form a two-layer structure, and for a sample having a predetermined thickness t of 30 μm, FIG. As shown in FIG. 9, the number of immersions was set to three to form a three-layer structure, and the sample having a predetermined thickness t of 15 μm was set to a four-layer structure with the number of immersions set to four as shown in FIG.
Moreover, the said longitudinal direction range M was adjusted by adjusting the immersion depth after the 2nd time.

These gas sensor elements 2 have a cross-sectional area of 6.84 mm ² perpendicular to the longitudinal direction in the heating region, and the length (projection amount) A of the protrusion 52 is 3 mm.
Table 2 and FIG. 10 show the results of the water cracking test similar to Example 1 described above.

  As can be seen from Table 2 and FIG. 10, the rate of water cracking decreases as the proportion of the longitudinal range M increases, and the rate of water cracking decreases as the predetermined thickness t of the protrusion 52 increases. To do. However, for the sample with the predetermined thickness t of the protrusion 52 of 15 μm, even when the ratio of the longitudinal range M was increased to 95%, water cracking occurred. Moreover, about the sample whose predetermined thickness t of the protrusion part 52 is 30 micrometers, and a 45-micrometer sample, when the ratio of the longitudinal direction range M is 80% or more, it is possible to prevent a water crack.

From the above results, in the thinnest portion in the cross section orthogonal to the longitudinal direction, the protruding portion 52 from which the porous protective layer 5 protrudes has a thickness of 30 μm or more in a range of 80% or more in the longitudinal direction. It turns out that it is preferable.
In addition, when employ | adopting the manufacturing method as shown in the said Example 2, since the inclined edge part 51 (refer FIG. 4) is inevitably produced, it is difficult to make the said longitudinal direction range M larger than 95%. is there.
Therefore, the protrusion 52 preferably has a thickness of 30 μm or more in a range of 80 to 95% in the longitudinal direction in the thinnest portion in the cross section orthogonal to the longitudinal direction.

Sectional explanatory drawing which shows the gas sensor using a gas sensor element in Example 1. FIG. Sectional explanatory drawing which shows typically the cross section of the heating area | region of the gas sensor element in Example 1. FIG. Sectional explanatory drawing which shows typically the formation state of the heating area | region in a gas sensor element in Example 1. FIG. Sectional explanatory drawing which shows typically a part of longitudinal direction of the other side part of the gas sensor element in Example 1. FIG. Sectional explanatory drawing which shows typically the formation state of the heating area | region in the other gas sensor element in Example 1. FIG. Sectional explanatory drawing which shows typically a part of longitudinal direction of the other side part of the other gas sensor element in Example 1. FIG. The graph which shows the relationship between the protrusion amount of a porous protective layer and the incidence rate of water cracking in Example 1. The graph which shows the relationship between the protrusion amount of a porous protective layer and the fall rate of sensor active time in Example 1. FIG. The graph which shows the relationship between the ratio of the longitudinal direction range M more than the predetermined thickness t in Example 3, and a moisture cracking incidence. The graph which shows the relationship between the protrusion amount of a porous protective layer in Example 3, and the decreasing rate of moisture intensity and sensor active time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Gas sensor element 3 Sensor board 31 Solid electrolyte body 32A, B electrode 4 Heater board 401 Heat generating part 402 Lead part 41 Ceramic body 42 Heat generating body 5 Porous protective layer 51 End part A Protruding amount L Longitudinal direction L1 One side L2 The other ~ side

Claims (4)

A sensor substrate in which a pair of electrodes are provided on both surfaces of a solid electrolyte body having oxygen ion conductivity, and a heater substrate in which a heating element that generates heat when energized is provided on a ceramic body having electrical insulation. In the gas sensor element,
The heating element has a heat generating portion formed by meandering a conductor, and a lead portion by a conductor drawn from both ends of the heat generating portion,
The gas sensor element has, on one side in the longitudinal direction, a heating region where the heat generating portion and the sensor substrate are opposed to each other, and the entire heating region is formed with a large number of pores made of ceramic particles. Covered with a porous protective layer,
The other end in the longitudinal direction of the porous protective layer protrudes from the other end in the longitudinal direction of the heat generating portion within a range of 3 mm toward the other side in the longitudinal direction. .   In Claim 1, the protruding portion in which the porous protective layer protrudes from the other end in the longitudinal direction to the other side in the longitudinal direction in the heat generating portion is the thinnest portion in the cross section orthogonal to the longitudinal direction. A gas sensor element characterized in that a range of 80 to 95% in the longitudinal direction has a thickness of 30 μm or more.   3. The porous protective layer according to claim 1, wherein the end portion on the other side in the longitudinal direction is formed in an inclined shape or a step shape in which the thickness decreases toward the other side in the longitudinal direction. A characteristic gas sensor element. In the method for manufacturing the gas sensor element according to any one of claims 1 to 3,
After the immersion process of immersing the gas sensor element in the ceramic material containing the ceramic particles in a solvent and the drying process of drying the ceramic material adhered to the surface of the gas sensor element, heat treatment is performed after repeating 2 to 5 times. And producing the porous protective layer by performing the method.

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