JP2009080111A - Gas concentration detecting element and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas concentration detecting element which is equipped with a porous protection layer having high water resistance, can be activated earlier and is excellent in response, and to provide a method of manufacturing the same. <P>SOLUTION: The gas concentration detecting element 10 is configured to detect a concentration of a specific gas component in a gas to be measured. The gas concentration detecting element 10 includes the porous protection layer 170 for covering the surface of the gas concentration detecting element 10 exposed to the gas to be measured. In the porous protection layer 170, at least one recess P<SB>MAC</SB>is disposed, which is made recessed so that its surface may face the element side, and opens to the surface of the porous protection layer 170. Since the aperture part P<SB>MAC</SB>is disposed therein, droplets are speedily spread in the porous protection layer 170 when being under water, thereby absorbing a thermal shock. Since the thickness of the porous protection layer 170 can be made thin to keep its heat capacity lowered, a solid electrolyte layer 100 can be activated early. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an improvement in water exposure strength of a gas concentration detection element used in a gas sensor for measuring the concentration of a specific gas component contained in combustion exhaust of an internal combustion engine such as a vehicle engine.

Conventionally, a combustion sensor for an internal combustion engine has been provided with a gas sensor for detecting the concentration of a specific gas component such as oxygen or nitrogen oxide contained in the combustion exhaust gas in a combustion exhaust flow path of an internal combustion engine such as a vehicle engine. It is carried out.
Such a gas sensor includes, for example, an oxygen ion conductive solid electrolyte layer formed in a flat plate shape, a measurement electrode layer formed on one surface of the solid electrolyte layer and in contact with the gas to be measured, and the measurement A porous diffusion resistance layer that is formed on the electrode layer side and transmits the gas to be measured, a reference electrode layer that is formed on the other surface of the solid electrolyte layer and is in contact with the reference gas, and is formed on the reference electrode layer side. A laminated gas concentration detecting element is built in which a reference gas chamber forming layer having a reference gas chamber for introducing the reference gas and an insulating substrate having a heating element are laminated.

The combustion exhaust contains poisonous substances composed of oil-containing components such as P, Ca, Zn, and Si and gasoline-added components such as K, Na, and Pb. There is a possibility that the layer and the porous diffusion layer may be contaminated and deteriorated by these poisoning substances, which may cause problems such as deterioration in response of the gas sensor and abnormal output.
For this reason, it is known to form a porous protective layer for capturing the poisonous substance on the outer peripheral surface of the porous diffusion layer of the gas concentration detecting element (see Patent Document 1).

  The combustion exhaust gas also contains water vapor, which condenses into water droplets and may adhere to the stacked gas concentration detection element. On the other hand, the laminated gas concentration detecting element is used in a state where the solid electrolyte layer is activated by being heated to a high temperature of 700 ° C. or higher by a heating element. For this reason, there is a possibility that a large thermal shock is applied to the stacked gas concentration detection element due to the adhesion (water exposure) of water droplets, resulting in water cracking.

Therefore, a technology is disclosed in which the porous protective layer is formed to a thickness equal to or greater than a predetermined thickness, and when water droplets adhere, the water droplets are dispersed in the porous protective layer to prevent cracks from occurring in the entire device. (See Patent Documents 2 and 3).
Japanese Patent Laid-Open No. 06-174683 JP 2006-171013 A JP 2006-250537 A

However, increasing the thickness of the porous protective layer improves the durability against thermal shock caused by water exposure, but increases the heat capacity, making early activation difficult and reducing the response of the gas concentration detection element. There is a risk of doing.
In addition, the porous protective layer is made of a heat-resistant ceramic material such as spinel or alumina to capture poisonous substances and ensure the permeability of the gas to be measured. Forming. Therefore, the bonding force between the particles is much weaker than that of a dense sintered body. For this reason, when the film thickness of the porous protective layer is increased, it has been found that the adhesion strength with the stacked gas concentration detection element becomes weaker and may peel from the element surface.

  Therefore, in view of such circumstances, the present invention has an object to provide a gas concentration detecting element that has a porous protective layer with high durability against water and is activated at an early stage and excellent in responsiveness, and a manufacturing method thereof. It is what.

A first invention provides a gas concentration detecting element for detecting the concentration of a specific gas component in a gas to be measured.
The gas concentration detection element comprises a porous protective layer covering the surface of the gas concentration detection element exposed to the gas to be measured,
The gas concentration detecting element is characterized in that the surface of the porous protective layer is recessed toward the element side, and at least one recess is formed in the surface of the porous protective layer. Item 1).

  In general, it has been considered that the porous protective layer should be formed uniformly. However, in the gas concentration detection element having the conventional porous protective layer, since the surface of the element is heated to an extremely high temperature during use, even if a small water droplet contacts the surface of the porous protective layer, Since the surface tension of the water droplets is small, the surface of the uniform porous protective layer does not get wet, rolls so that it is repelled on the surface, and when the small water droplets gather and become large water droplets, the surface tension increases. It was found that the surface of the protective layer wets and spreads, and instantaneously penetrates into the porous protective layer at a stroke, so that the thermal shock increases and the device is subject to water cracking.

According to the first aspect of the present invention, when the water droplets that have come into contact with the surface of the gas concentration detection element are caught by the concave portions, the surface tension balance is lost even with small water droplets, and the porous protective layer is quickly obtained. Can be diffused and immediately dried. In addition, since the water droplets contact the porous protective layer with a certain probability on the side wall of the concave portion where the water droplets are captured, the thermal shock is relatively small and it is difficult to cause water cracking. That is, the moisture in the gas to be measured that comes into contact with the porous protective layer is absorbed by the side surface of the recess that is recessed toward the inside of the gas concentration detection element before reaching the surface of the gas concentration detection element. In the protective layer, it can spread in the surface direction of the gas concentration detecting element. Thereby, the porous protective layer can be provided with water absorption in the surface direction of the gas concentration detecting element, and the gas concentration detecting element can be hardly caused to undergo water cracking.
In addition, since the water droplets can be quickly captured by the concave portion, the volume of the entire porous protective layer can be reduced.
Accordingly, the heat capacity of the entire porous layer is lowered, and the activation speed as a sensor is increased, so that the response can be remarkably improved.

  According to a second invention, in the method for producing the gas concentration detecting element of the first invention, the gas concentration detecting element is immersed in a slurry in which heat-resistant ceramic particles are dispersed, and this is dried and calcined. And a porous protective layer forming step for forming a porous protective layer covering the surface of the gas concentration detecting element. (17) A method for producing a gas concentration detecting element.

  According to the second aspect of the present invention, the porous protective layer is provided in an extremely simple manner without requiring a significant process change from the conventional one, and is excellent in response and excellent in durability against water. A gas concentration detecting element can be manufactured.

According to a third aspect of the present invention, there is provided a method for manufacturing the gas concentration detection element according to the first aspect, wherein the gas concentration detection element is immersed in a slurry containing ceramic particles in a solvent, and the gas concentration detection is performed. Repeatedly performing a drying step of drying the ceramic material adhering to the surface of the element, and then performing a heat treatment step of heat-treating the dried ceramic material to form a porous protective layer on the surface of the gas concentration detecting element, In forming the porous protective layer,
In the method of manufacturing a gas concentration detecting element, the concave portion is generated on the surface of the ceramic material when performing the second and subsequent drying steps (claim 19).

The method for producing a gas concentration detecting element according to the third aspect of the invention is a method capable of effectively forming the recesses in the porous protective layer.
In the manufacturing method of the present invention, in the process of repeating the dipping process and the drying process, the concave portion is generated on the surface of the ceramic material adhering to the surface of the gas concentration detecting element when the second and subsequent drying processes are performed. be able to. Thereby, a special construction method is not required to form the recess, and the recess can be easily formed.

  Therefore, according to the method for manufacturing the gas concentration detecting element, it is possible to easily manufacture a gas concentration detecting element that can effectively improve durability and responsiveness.

A preferred embodiment of the above-described gas concentration detecting element of the present invention and the method for manufacturing the same will be described.
The porous protective layer may be composed of one or more of alumina, spinel, titania, zirconia, and mullite particles as ceramic particles.

It is preferable that the opening of the recess is visible with the naked eye (Claim 2).
In this case, the water cracking suppressing effect by the concave portion can be more remarkably exhibited.
From the same viewpoint, more preferably, the opening of the recess has an equivalent circle diameter of 0.1 (mm) or more.
When the equivalent circle diameter is less than 0.1 (mm), the significance of forming the concave portion is lowered, and it may be difficult to sufficiently reduce the heat capacity.
The circle-equivalent diameter is a diameter of a circle having the same area as the area (opening) of the recess that opens on the surface of the porous protective layer.

The concave portion is a range satisfying the relationship of Formula 1 when one side of the minimum square S _Q1 circumscribing the opening of the concave portion is a (mm) and the depth D _{P of the} concave portion is b (mm). It is desirable to form by (claim 4).
i = (b / 0.008 + 1), {(1−0.27 / a) ² } ⁱ ≦ 0.0027 (Equation 1)

If the concave portion is formed within the range satisfying the relationship of the above mathematical formula 1 according to the test of the present inventor, water droplets of 0.01 (mm ³ ) to 3 (mm ³ ) that may cause water cracking of the element due to the concave portion. It has been found that water droplets captured and wetted can be quickly diffused and evaporated in the porous protective layer without reaching the surface of the concentration detection element, and water cracking can be effectively suppressed.
Incidentally, if the volume of the water droplets 0.01 mm ³ or less, thermal shock that occurs not occur the destruction of the element becomes less stress heat resistance of the gas concentration detecting element itself also on the structure of the sensor, 3 (mm ³ ) It has been found that the above water droplets do not get wet.

In addition, when the thickness T ₃ of the porous protective layer at the formation site of the recess is c (μm), it is preferable that the relationship of Formula 2 is satisfied (Claim 5).
C ≧ 25 Formula 2

  If the concave portion is set in the range of the mathematical formula 2, a porous layer exists at the bottom portion of the concave portion, and water droplets entering from the opening portion of the concave portion diffuse into the porous surface existing on the inner peripheral wall surface of the concave portion. And immediately dried. For this reason, a thermal shock is relieve | moderated and becomes small, and it can make it hard to raise | generate a water-proof crack. Therefore, it is possible to realize a highly responsive gas sensor in which the thickness of the entire porous protective layer is reduced, the heat capacity is lowered, and the activation speed of the element is increased. In addition, when the thickness of the porous protective layer in the portion where the concave portion is formed is thinner than the range of the present invention, water droplets cannot diffuse into the porous interior and reach the element surface, resulting in water cracking. There is a risk of causing.

Further, when one side of the minimum square S _Q1 circumscribing the opening of the recess is defined as a (mm), it is preferable that the relationship of Formula 3 is satisfied (Claim 6).
0.27 ≦ a ≦ 1.8 Formula 3

By the opening of the recess is deeper the depth D _P The larger water droplets are found to be lower the probability of reaching the surface of the device, by forming an opening in the range of the equation 3, 0. It has been found that water droplets from 01 (mm ³ ) to 3 (mm ³ ) can be captured most effectively.

Moreover, it is preferable that the relationship of Formula 4 is satisfied when a plurality of the recesses are provided and the distance L _p between the recesses is d (mm).
d ≧ 1.8 Formula 4

In this case, since water droplets can be captured by the plurality of recesses, water cracking is less likely to occur. If the distance L _P between the recesses is provided in the range of Equation 4, the plurality of openings do not overlap each other, and each can catch water droplets independently, so that water droplets can be captured more effectively. .

In the porous protective layer, it is preferable that a bowl-shaped groove is formed in which the concave portions extend continuously.
In this case, water droplets can be more reliably captured by the ridge-shaped grooves spreading on the surface of the porous protective layer, so that water cracking is less likely to occur. That is, in this case, the recess is formed in a groove shape having a pair of inclined side surfaces in a cross section orthogonal to the direction in which the bowl-shaped groove is formed. Then, the moisture in the gas to be measured that contacts the bowl-shaped groove in the porous protective layer can be absorbed by the porous protective layer on the pair of inclined side surfaces, and the surface of the gas concentration detecting element can be more quickly Can spread in the direction. Therefore, the water absorption by a recessed part can be improved.

The average width a between a pair of peak vertices in a cross section orthogonal to the direction in which the bowl-shaped groove is formed is 0.05 to 0.8 (mm), and the entire direction in which the bowl-shaped groove is formed It is preferable that the average depth b of the bottom part located between a pair of mountain vertices is 0.05-1 (mm).
In this case, the size and shape of the recess are appropriate, and the water absorption can be improved more effectively.
The average width a is determined as the average value of the widths between a pair of mountain vertices at a plurality of locations in the direction of forming the recesses. The average depth is a depth from the lower peak to the bottom of the pair of peaks, and is determined as an average value of the depths at a plurality of locations in the direction of forming the recesses.

When the average width a is less than 0.05 (mm) and the average depth b is less than 0.05 (mm), there is a possibility that the water absorption by the recesses cannot be sufficiently exhibited. Further, when the average width a exceeds 0.8 (mm) and the average depth b exceeds 1 (mm), it is necessary to increase the thickness of the porous protective layer, There is a possibility that the responsiveness of the gas concentration detecting element cannot be secured.
Moreover, it is preferable that the projection length projected to the longitudinal direction of the said gas concentration detection element is 1 (mm) or more. Moreover, this projection length receives a restriction | limiting from the longitudinal direction length of a porous protective layer, for example, can be 15 (mm) or less.
Moreover, the said recessed part can be formed in the shape where the average width e (mm) between a pair of peak parts in the part of 1/3 length from the said bottom part becomes smaller than the said average width a.

As the gas concentration detection element, a so-called stacked gas concentration detection element can be employed.
That is, for example, the gas concentration detecting element includes at least an oxygen ion conductive solid electrolyte layer formed in a flat plate shape, and a measurement electrode layer formed on one surface of the solid electrolyte layer and in contact with the gas to be measured. A porous diffusion resistance layer that is formed on the measurement electrode layer side and transmits the gas to be measured; a reference electrode layer that is formed on the other surface of the solid electrolyte layer and is in contact with the reference gas; and the reference electrode layer side A laminated gas concentration detecting element in which a reference gas chamber forming layer having a reference gas chamber for introducing a reference gas and an insulating substrate having a heating element that generates heat when energized is laminated. (Claim 10).

  Such a laminated gas concentration detecting element includes a solid electrolyte layer forming step of forming a flat solid electrolyte layer using a slurry in which ceramic powder made of an oxygen ion conductive solid electrolyte is dispersed, and the solid electrolyte layer Using a measurement electrode layer forming step of printing a measurement electrode layer on one surface, a measurement electrode layer forming step of printing a reference electrode layer on the other surface of the solid electrolyte layer, and a slurry in which an insulating material is dispersed An insulating substrate forming step for forming a flat insulating substrate, a reference gas chamber forming step for forming a reference gas chamber forming layer for introducing a reference gas by cutting out a part of the insulating substrate, and the insulating A heating element forming step of printing a heating element on the surface of the conductive substrate, a stacking step of stacking these to form a gas concentration detecting element member stack, and firing the gas concentration detecting element member stack Ga It can be produced by a production method comprising a sintering step of obtaining a concentration detection element.

  Further, for example, the gas concentration detection element includes a sensor substrate having a pair of electrodes on both surfaces of a solid electrolyte body having oxygen ion conductivity, and a heating element that generates heat by energizing a ceramic body having electrical insulation. A heater substrate provided and a diffusion resistance layer made of a porous body that allows a gas to be measured to be in contact with one of the pair of electrodes to pass through are laminated, and the diffusion resistance layer is formed on one of the sensor substrates. It is also possible to make a laminated gas concentration detecting element which is laminated on the surface on the side and the heater substrate is laminated on the surface on the other side of the sensor substrate.

The heating element has a heating part formed by meandering a conductor, and a lead part by a conductor drawn out from both ends of the heating part, and the gas concentration detection element is on one side in the longitudinal direction, It is preferable that the heating portion and the sensor substrate have a heating area facing each other, and the entire heating area is covered with the porous protective layer.
As described above, the porous protective layer covering the heating region is liable to cause the above-described problem of water cracking. Therefore, in this case, the effect of the present invention, that is, prevention of water cracking by forming the concave portion, can be exhibited more remarkably.

It is preferable that at least a part of the concave portion is formed in a portion facing the heating region.
In this case, the concave portion can be formed in a portion that is susceptible to a thermal shock due to water, and the durability of the porous protective layer and the gas concentration detecting element can be further improved by the concave portion.

It is preferable that the concave portion is formed at one or a plurality of locations on the surface in the stacking direction in which the sensor substrate and the heater substrate are stacked.
In this case, the recesses can be easily formed and the water absorption of the porous protective layer can be more effectively exhibited.

Further, as the gas concentration detection element, a so-called cup-type gas concentration detection element may be employed.
That is, the gas concentration detection element is provided on the outer surface of the cup-type oxygen ion conductive solid electrolyte body, one of which is closed and a reference gas chamber is provided inside, and to be measured. It consists of a measurement electrode that comes into contact with the gas and a reference electrode provided on the inner surface of the solid electrolyte body, and an insulating base that has a heating element that generates heat when energized is inserted and disposed in the reference gas chamber. A cup-shaped gas concentration detecting element can be obtained.

  Next, in the production method of the second invention, a precursor made of either air bubbles or organic particles or an emulsion that can be burned down during calcination is dispersed in the slurry, and the concave portion is formed on the surface of the porous protective layer. Preferably, a forming step of forming is provided (claim 17).

  In this case, the precursor forms a concave portion after calcination, and a gas concentration detecting element excellent in response and durability against water can be manufactured very easily.

Next, in the manufacturing methods of the second and third inventions, the ceramic particles are preferably made of alumina particles having an average particle size of 25 (μm) or less.
In this case, the concave portion can be more effectively formed on the surface of the porous protective layer.
The average particle size of the ceramic particles is more preferably 20 (μm) or less. Moreover, the lower limit value of the average particle diameter of the ceramic particles can be set to, for example, 10 (μm) or more as a particle diameter suitable for generating a recess. More preferably, it is 12 (μm) or more, and more preferably 15 (μm) or more.

The porous protective layer is preferably formed using the slurry having a viscosity of 200 to 1200 (mPa · s).
In this case, it becomes easy to form a recess in the surface of the porous protective layer. In particular, when the viscosity is increased, it becomes easier to form the recesses, and the recesses can be easily formed by immersing the gas concentration detecting element in the slurry, drying, and firing without using the above-described precursor or the like. be able to.
When the viscosity of the slurry is less than 200 (mPa · s), it may be difficult to form a recess on the surface of the porous protective layer. More preferably, it is 400 (mPa · s) or more. On the other hand, when the viscosity of the slurry exceeds 1200 (mPa · s), the adhesion of the porous protective layer is lowered, and there is a possibility that the slurry is easily peeled off. More preferably, it is 700 (mPa · s) or less.

Before the porous protective layer is formed, the gas concentration detecting element is immersed in a slurry for forming a fine particle porous layer containing ceramic particles having an average particle diameter of 1 to 9 (μm) and dried. By forming the porous protective layer using a slurry for forming a porous protective layer containing ceramic particles having an average particle size of 13 to 25 (μm) as the slurry for forming a porous protective layer, fine particle porous protection is achieved. Preferably, the porous protective layer is laminated on the layer (claim 21).
In this case, the gas concentration detecting element in which the porous protective layer made of relatively coarse ceramic particles is laminated on the fine particle porous layer made of relatively fine ceramic particles can be manufactured. In such a gas concentration detecting element, the porous protective layer can be mainly responsible for improving the water-repellent performance, and the fine-particle porous layer can be responsible for trapping poisonous substances. By forming the fine particle porous layer, the poisoned substance that has passed through the recess and passed through the porous protective layer can be reliably trapped by the fine particle porous layer.

When the average particle size of the ceramic particles of the fine particle porous layer forming slurry is less than 1 μm, clogging may occur. On the other hand, if it exceeds 9 μm, the trap effect of the fine particle porous layer forming slurry on poisonous substances may be reduced.
When the ceramic particles of the slurry for forming a porous protective layer are less than 13 μm, it may be difficult to sufficiently form the recesses. On the other hand, when it exceeds 25 μm, the adhesion strength between the porous protective layers or between the porous protective layer and the element is lowered, and there is a possibility that peeling easily occurs.

As the slurry for forming the fine particle porous layer, one having a viscosity of 11 to 600 mPa · s can be employed.
When a material having a viscosity of 200 mPa · s or more is employed within the above range, the concave portion can be easily formed in the fine particle porous layer.
When the viscosity is less than 11 mPa · s, it may be difficult to sufficiently adhere the slurry for forming the fine particle porous layer to the gas concentration detecting element by dipping. On the other hand, if it exceeds 600 mPa · s, the poisoning effect of the fine particle porous layer may be reduced. Moreover, there exists a possibility that the adhesiveness of the said fine particle porous layer may fall. More preferably, it is 150 mPa · s or less, and more preferably 100 mPa · s or less.

  The average particle diameter of the above-mentioned slurry can be measured by, for example, a laser diffraction type particle size distribution meter. The viscosity can be measured by, for example, a B-type rotational viscometer.

(Example 1)
Hereinafter, a gas concentration degree detection element 10 and a gas sensor 1 having the same according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a main part of a gas concentration detecting element 10 to which the present invention is applied. 2 (a) and 2 (b) are theoretical explanatory diagrams for defining the size of the recess _PMAC , FIGS. 3 (a) and 3 (b) are characteristic diagrams showing the effects of the present invention, and FIG. 1 shows an overall configuration of a gas sensor 1 to which a gas concentration detection element 10 of the present invention is applied.

As shown in FIG. 1, in the gas concentration detecting element 10, a solid electrolyte layer 100 made of an oxygen ion conductive ceramic material such as zirconia is formed in a flat plate shape, and a gas to be measured is formed on one surface thereof. A measurement electrode layer 110 to be exposed is formed, and a reference electrode layer 120 to be exposed to a reference gas such as the atmosphere is formed on the other surface of the solid electrolyte layer 100. Further, a reference gas chamber forming layer 141 for forming a reference gas chamber 140 for introducing a reference gas is formed on the reference electrode layer 120 side, and an insulating base 150 having a heating element 151 inside is formed. Yes. A diffusion resistance layer 130 is formed on the measurement electrode layer 110 side of the solid electrolyte layer 100 so as to cover the measurement electrode layer 100. Further, the outer periphery of the gas concentration detecting element 10 is formed with a fine particle porous layer 160 composed of fine submicron particles, and further covers the surface to form a porous protective layer 170. The surface of the porous protective layer 170 recess P _MAC that is recessed toward the device side is provided at least one place or more.

In the present embodiment, the porous protective layer 170 is a porous film made of alumina having an average particle diameter of about 20 μm and dispersed with pores P _MIC having an opening diameter O _MIC of about 20 μm, and the film thickness T1 thereof is about 400 μm. Is formed.
Further, the concave portion P _MAC which is the main part of the present invention has a pinhole shape having an opening diameter, that is, an opening diameter O _MAC of about 0.27 mm to 1.8 mm and a depth DP of about 60 μm to 400 μm, or The film thickness T3 of the porous protective layer 170 at the bottom of the portion where the concave portion _PMAC is formed, which is formed into a continuous ridge shape, is 25 μm or more.
Opening diameter O _MIC pores P _MIC is the measurement gas can be passed through a relatively having a large grain size P, Ca, Zn, oil-containing component of Si contained in the combustion exhaust gas, K, Na, Pb, etc. Since the poisoning substances such as gasoline additives, PM (spherical substances), and incomplete combustion substances of fuel are captured, the poisoning substances do not reach the surface of the gas concentration detecting element 10.
The diameter of the opening of the recess P _MAC is a 0.1mm over a circle equivalent diameter can be sufficiently visible to the naked eye.

Here it will be described in detail recess P _MAC is an essential part of the present invention.
As shown in FIG. 2 (a), drawing a virtual circumscribing square S _Q1 circumscribing the opening P _MAC recess, the one side and a (mm). Then, the (b), the case where spherical particles of a water molecule with a radius R is invading into the virtual circumscribing square S _Q1, one side where the center of the particles indicated by two-dot chain line a-2R (mm) The water molecules W _d1 and water molecules W _d2 completely contained in the virtual square S _Q2 may reach the surface of the gas concentration detection element 10 without touching the inner peripheral wall surface of the recess P _MAC .
On the other hand, water droplets, to reach toward the inside of the recess P _MAC having a depth D _P to the surface of the device, it is necessary to consider the probability of passing without contacting the surfaces of the recess portion P _MAC.
Water drop W _d3 center is located outside of the imaginary square S _Q2 is in contact with the wall surface of the recess P _MAC porous protective layer, to be water cracking device since the water droplets in the porous open to the surface thereof to diffuse Do not wake up.

When the water droplet amount is V (mm ³ ), the particle diameter R (mm) of the water droplet is expressed as V = (4/3) πR ³ . When the probability P _i that water droplets reach the surface of the device through the opening P _MAC, water droplets arrival probability P _i is dependent on the depth D _P of the concave portion, the depth D _P of the concave portion b (mm ), The following relationship holds.
P _i = {(1-2R / a) ² } ⁱ i = (b / 0.008 + 1)

When the maximum amount of water droplets to be wet is V (mm ³ ), it is necessary to have the performance of catching water droplets of 0.01 mm ³ to 3 mm ³ and quickly diffusing into the porous protective layer 170. The particle diameter R (mm) of the water droplet is expressed as V = (4/3) πR ³ . The probability P that water droplets can pass through the virtual circumscribed square S _Q1 is recognized as the probability of Gordan being expressed by the ratio of the area (a−2R) ² of the passable range to the opening area a ² . It holds.
P = (a-2R) ² / a ² = (1-2R / a) ²

The reach of the water droplets can be tested in a state where the mesh of the sieve having the hole of the virtual square a is overlapped in the depth direction, and the number of meshes to be screened and the number of times i have the same relationship.
Now, assuming that N water droplets having the same radius R do not contact the net, N · P water droplets can pass through the net. When the passed N · P water droplets pass through the next net, (N · P) (N · P) can pass. Similarly, (N · P) ⁱ water droplets pass through the i-th time.
That is, the probability Pi that a water droplet passes through the i-th net and reaches the element is expressed by the following equation.
P _i = {(1-2R / a) ² } ⁱ
The relationship of the variable i as a function with respect to the direction of the depth D _P of the recess was obtained by experiments.
In the experiment, a φ1.5 mm macropore was drilled in the porous protective layer, and the thickness of the porous protective layer was cut to the macropore depth to obtain a test sample.
FIG. 3 shows the arrival rate obtained by electrically checking whether or not water droplets were dropped 500 times from 10 mm above the macropores and the water droplets reached the bottom. The experiment was performed by changing the amount of water droplets from 0.01 mm ³ to 0.1 mm ³ .

Next, as a result of approximating the variable i related to the depth D _P direction of the concave portion with a geometric distance function of the depth D _P of the concave portion, as shown in FIG. 3, the relationship of i = (b / 0.008 + 1) is obtained. It was found that it was almost consistent with the experimental data.
In FIG. 3, points indicate experimental values, and curves indicate calculated values.
Thus, by opening P _MAC is deeper the depth D _P if large, water droplets were found to be lowered a probability Pi that reaches the surface of the device.

In order for the element not to cause water cracking, it is necessary to ensure 99.73% of the probability that the water droplet does not reach the element surface. That is, the probability P _i that a water droplet reaches the element surface needs to be 0.27% or less.
In the present embodiment, the maximum amount of water is suppressed to 0.1 mm ³ or less by a cover outer cylinder 410 and a cover inner cylinder 400 described later.
As shown in FIG. 3, it was clarified by calculation and experiment that the smaller the size of the opening and the water droplet, the higher the arrival rate to the element.
Therefore, the element is protected from water droplets by the water-covered covers 400 and 410, and the value of R which is 0.01 mm ³ of the smallest water droplet is 0.134 mm as the water droplet that starts to break the device.

As described above, in order to prevent water droplets from reaching the element surface, the side of the virtual circumscribed square S _Q1 circumscribing the opening diameter O _MAC of the opening P _MAC of the recess is defined as a (mm), and the depth D _P of the recess is defined as b. Assuming (mm), a and b satisfy the relationship of Equation 1.
i = (b / 0.008 + 1), {(1−0.27 / a) ² } ⁱ ≦ 0.0027 (Equation 1)

Further, when the depth D _P of the recess satisfies Equation 1, the recess is set so as to satisfy the relationship of Equation 2 when the thickness T ₃ of the porous protective layer 170 at the bottom of the recess is c (μm). if the probability that a large water droplets can pass through the opening P _MAC recess small, reaches the porous bottom portion smaller water droplets. However, small water droplets diffuse into the porous material at the bottom of the opening and therefore cannot reach the element surface directly, and thermal shock is not easily transmitted to the element itself.
It has been experimentally found that the porous material present at the bottom of the recesses diffuses water droplets inside and is immediately dried, reducing thermal shock and making it difficult to cause water cracking.
If the thickness T ₃ of the porous protective layer 170 at the bottom of the recess is smaller than this range, the water droplets may reach the surface of the element before being diffused into the porous body, which may cause water cracking.
c ≧ 25 Formula 2

When one side of the virtual circumscribed square S _Q1 circumscribing the opening P _MAC in the recess is a (mm), if the opening P _MAC is formed in a range satisfying the relationship of Formula 3, from 0.01 (mm ³ ) It is possible to catch water droplets in the range of 3 (mm ³ ) with the porous existing on the side surface of the recess.
0.27 ≦ a ≦ 1.8 Formula 3

Or providing a plurality of recesses, if the wrinkle-shaped groove recess is continuous with the continuous, it becomes more difficult to be water cracking occurs it is possible to capture water droplets by a plurality of openings P _MAC. If the distance L _P between the recesses and the bowl-shaped grooves is d (mm) and provided within a range satisfying Equation 4, the plurality of recesses and the bowl-shaped grooves do not overlap each other, and each of them independently receives water droplets. Since it can be captured, water droplets can be captured more widely and effectively. Thereby, the porous volume can be reduced.
The bowl-shaped groove is a groove having a continuous opening having a continuous width of at least twice the minimum width a.
d ≧ 1.8 Formula 4

FIG. 4 shows an overall configuration of the gas sensor 1 including the stacked gas concentration detecting element 10 of the present invention.
The gas sensor 1 includes a laminated gas concentration detection element 10, a housing 300 that holds the gas concentration detection element 10 inside the holding member 200, and a cover that covers a portion of the gas concentration detection element 10 that is exposed to the gas to be measured. A casing 310 for holding a pair of energization wires 210 and 220 for supplying power to the heat generating part of the bodies 400 and 410 and the gas concentration detecting element 10 and a pair of signal wires 230 and 240 for taking out an output signal from the gas concentration detecting element 10 It is constituted by.
The housing 300 is made of a metal such as stainless steel and is formed in a substantially cylindrical shape. A casing 310 is fitted on the boss 304 on the proximal end side, and cover bodies 400 and 410 are fixed on the distal end side 301. Yes. A screw portion 302 is formed on the middle outer peripheral portion of the housing 300 and is screwed to an exhaust flow channel wall 500 (not shown) via a gasket 340 so that the distal end side of the gas concentration detection element 10 is in the measured gas flow channel. It is fixed in a state covered with the cover bodies 400 and 410.
The housing 300 is formed with a hexagonal portion 303 for tightening the screw portion 302.

The cover bodies 400 and 410 are made of a heat-resistant metal such as stainless steel and have a double cylinder structure composed of a substantially bottomed cylindrical inner cover 400 and an outer cover 410.
The inner cover 400 and the outer cover 410 are respectively provided with openings 401, 402, 411, and 412 for introducing water to be measured into the gas and detecting the water concentration of the gas concentration detection element. The flange portions 403 and 413 are fixed to the crimping portion 301 of the housing 300 by caulking.

The gas concentration detecting element 10 is fixed inside the housing 300 while ensuring insulation with the housing 300 by the insulator 200.
Further, a seal member 202 is interposed between the insulator 200 and the housing 300, and the gas concentration detection element 10 and the insulator 200 are fixed by a sealing member such as glass, and the measured gas side and the reference gas side And is isolated. The portion of the gas concentration detection element 10 exposed to the gas to be measured is covered with the porous protective layer 170 which is the main part of the present invention, and the gas concentration detection in the tip portion 180 of the porous protective layer 170, that is, the porous protective layer 170. A concave portion _PMAC is formed in the end portion 180 in the longitudinal direction of the element.
Since the water gas concentration detecting device 10 according to the entering of water drops from the opening 402 provided in the bottom portion of the outer cover 410 is likely to occur, it is effective to provide a recess P _MAC to the distal end of the porous protective layer 170. The concave portion _MAC can also be formed on the surface of the porous protective layer 170 other than the tip, for example, the surface of the porous protective layer 170 in a direction orthogonal to the longitudinal direction of the gas concentration detecting element. Thereby, it is possible to effectively suppress the water concentration of the gas concentration detection element 10 due to the intrusion of water droplets from the opening 401 of the outer cover 410.

  The pair of energizing wires 210 and 220 and the pair of signal wires 230 and 240 are held on the base end side of the casing 310 by the base end insulating sealing materials 320 and 330, and terminals are connected by the connection fittings 211, 221, 231, and 241. Connected to the metal fittings 212, 222, 232, 242 and connected to heating element energizing terminals 153a, 153b and output signal terminals 112, 122 of the gas concentration detecting element 10 described later.

  A reference gas inlet 312 is formed in the base end insulating sealing materials 320 and 330, and the atmosphere introduced from the reference gas inlet 312 through the water repellent filter 330 is the reference gas chamber of the gas concentration detection element 10. Has been introduced.

  When the heating element 151 is energized by an energization control device (not shown) and the solid electrolyte layer 100 is activated by the heating element 151, the oxygen concentration in the measurement gas in contact with the measurement electrode layer 110 via the diffusion resistance layer 130. And the difference in oxygen concentration in the atmosphere introduced into the reference gas chamber 140 in contact with the reference electrode layer 120 causes a potential difference between the electrodes, and by measuring this, the oxygen concentration in the gas to be measured can be detected.

FIG. 5 shows the effect of the present invention together with a comparative example using a conventional gas concentration detecting element provided with a porous protective layer. In this figure, (a) shows the occurrence rate of water cracking in a Weibull plot, (b) shows the film thickness of the porous protective layer, and (c) shows the air-fuel ratio with the theoretical air-fuel ratio λ ₀ as 1. The step response is shown in which 63% change time is measured by alternately changing λ from 0.9 to 1.1.

  As shown in FIG. 5A, the conventional comparative example 1 and the first embodiment of the present invention have substantially the same water cracking incidence, but as shown in FIG. In Example 1, it was possible to reduce the weight of the porous protective layer by about 17%, and as a result, step response was very good as shown in (c).

A method for manufacturing the gas concentration detection element 10 of the present invention will be described below.
FIG. 6 is a developed perspective view showing the configuration of the most basic gas concentration detecting element 10 and will be described as an example of the gas concentration detecting element 10 to which the present invention can be applied.
In the solid electrolyte layer 100, an oxygen ion conductive ceramic material such as zirconia is dispersed in a dispersion medium such as toluene and ethanol together with a binder such as polyvinyl butyral (PVB), a plasticizer such as dibutyl phthalate (DBP), and a dispersant. It is obtained by blending the slurry and using it to form a flat plate having a predetermined thickness by the doctor blade method or the like.

  A measurement electrode layer 110, a measurement electrode layer lead portion 111, a measurement electrode layer terminal portion 112, and a reference electrode layer are formed on one surface 101 of the solid electrolyte layer 100 using a mixed paste of platinum paste and the solid electrolyte layer slurry. The terminal portion 122 is printed and the reference electrode layer 120 and the reference electrode layer lead portion 121 are printed and formed on the other surface 102. The reference electrode layer lead portion 121 and the through hole 103 formed in the solid electrolyte layer 100 are formed. A through-hole electrode that is electrically connected to the reference electrode layer terminal portion 122 is formed by suction printing or the like.

  The reference gas chamber 140 is formed into a sheet shape by a doctor blade method using a slurry in which an insulating ceramic material such as alumina is dispersed in a dispersion medium together with PBV, DBP, a dispersing agent, etc. A plurality of reference gas chamber vertical wall forming layers 142 punched into a U shape and a plurality of reference gas chamber base forming layers 141 punched into a rectangle are stacked.

  The above-described alumina sheet is used to form a flat insulating base 150, and a heating element 191 and a pair of heating element lead portions 152 are printed on one surface using a paste obtained by mixing platinum paste and alumina slurry, A pair of heating element terminal portions 153 are printed on the other surface, and through-hole electrodes for conducting the heating element lead portions 152 and the heating element terminal portions 153 are provided in a pair of through-holes 154 formed in the insulating base 150. It is formed by suction printing or the like.

  The diffusion resistance layer 130 is printed and formed so as to cover the measurement electrode layer 110 using a paste in which a heat-resistant ceramic material such as alumina having a particle diameter larger than that of the above-described alumina sheet is dispersed in a dispersion medium together with a binder.

  These are laminated to form an integral laminated body by thermocompression bonding, adhesion, or the like, and this is degreased and sintered to form the gas concentration detecting element 10.

FIG. 7 shows the method of forming the fine particle porous layer 160 in the order of (a) to (c). Submicron-class alumina having a very small particle diameter is dispersed in a dispersion medium such as water or alcohol together with an inorganic binder to obtain a fine particle slurry (slurry for forming a fine particle porous layer) 161. The gas concentration obtained by the above-described steps A portion of the detection element 10 exposed to the gas to be measured (range indicated by L1 in the figure) is immersed and dried.
The fine particle slurry 161 is preferably homogenized by performing a process such as defoaming and aging in order to reduce internal defects.
In this example, as the fine particle slurry, an alumina particle having an average particle diameter of 4 μm and a viscosity of 13 mPa · s was used.
The average particle size was measured with a laser diffraction particle size distribution meter (MT3000 manufactured by Microtrac).
The viscosity was measured using a B-type rotational viscometer (RB-85L manufactured by Toki Sangyo Co., Ltd.). Specifically, the measurement is performed using the rotor No. 3. It was performed under conditions of a speed of 60 rpm and a temperature of 25 ° C., pot roller stirring was performed at 70 rpm for 5 hours or more, and the viscosity after 3 minutes.

In FIG. 8, the formation method of the porous protective layer 170 comprised with the coarse particle which is the principal part of this invention is shown in order of (a)-(c). Coarse alumina or the like having an average particle size of about 20 μm is dispersed in a dispersion medium such as water or alcohol together with an inorganic binder to obtain a coarse particle slurry (slurry for forming a porous protective layer) 172. The portion where the fine particle porous layer 160 is formed (range indicated by L2 in the figure) is immersed and dried. This immersion (a) and drying (b) are repeated a plurality of times until the film thickness of the unfired coarse particle porous layer 171 reaches a predetermined thickness. When this is dried and then calcined at a low temperature of about 900 ° C., the porous protective layer 170 of the present invention is completed.
In this example, as the coarse particle slurry 172, an alumina particle having an average particle diameter of 20 μm and a viscosity of 500 mPa · s was used. The average particle diameter and viscosity can be measured in the same manner as in the case of the above-described fine particle slurry.
During the coarse particle slurry 172 precursor P _REP such granules or emulsions comprising a burned possible organic by bubbles or calcination are dispersed. This precursor P _REP becomes a void by calcination to form a recess P _MAC having an opening. In this example, the precursor _PREP is used. However, as described above, the concave portion can be formed by using a slurry having a relatively high viscosity even if the precursor _PREP is not contained.
The dispersion concentration of the precursor _{PREP in} the coarse particle slurry 172 is such that the distance L _P between the plurality of openings, between the bowl-shaped grooves where the openings are continuously connected, and between the openings and the grooves is 1. It is desirable to adjust so that it may become 8 mm or more.

The gas concentration detection element 10 used for the gas sensor 1 which is the 1st Embodiment of this invention is completed according to the above process.
According to the present invention, the oxygen ion conductive solid electrolyte layer 100, the measurement electrode layer 110, the porous diffusion resistance layer 130, the reference electrode layer 120, and the reference gas chamber forming layer having the reference gas chamber 140 are provided. And covering the surface of the gas concentration detecting element 10 formed by laminating the insulating base 150 having the heat generating element 151 inside, the porous protective layer 170 is provided, and the surface of the porous protective layer 170 faces the element side. recess P _MAC at least 1 or more provided a gas concentration detecting device 10 is recessed Te is due to the presence of the recess P _MAC, rapidly water droplets when Himizu is diffused into the porous protective layer 170, to reduce thermal shock . Since the thickness of the porous protective layer 170 can be reduced and the heat capacity can be reduced, the solid electrolyte layer 100 can be activated at an early stage.

The present invention is not limited to the gas concentration detecting element having the most basic structure shown in the above embodiment and the manufacturing method thereof, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above-described embodiment, the gas concentration detection element used in a simple oxygen sensor in which the measurement unit includes only one cell has been described. It can also be applied to an accurate gas concentration detection element or the like.
An internal combustion engine to which the gas sensor provided with the gas concentration detection element of the present invention can be applied is a gasoline engine as long as it contains moisture and poisonous substances in the combustion exhaust and needs to protect the gas concentration detection element. The present invention can be applied not only to liquid fuel engines such as diesel engines but also to gas fuel engines such as natural gas.

(Example 2)
Next, another embodiment of the gas concentration detecting element will be described with reference to the drawings.
As shown in FIG. 10, the gas concentration detection element 7 of this example is formed by laminating a sensor substrate 8, a heater substrate 9, and a diffusion resistance layer 83 and firing them. The sensor substrate 8 has a measured gas side electrode 82A in contact with the measured gas on one surface of the solid electrolyte body 81 having oxygen ion conductivity. The sensor substrate 8 is used as a reference gas on the other surface of the solid electrolyte body 81. It has a reference gas side electrode 82B in contact therewith. The heater substrate 9 is provided with a heating element 92 that generates heat by energizing a ceramic body 91 having electrical insulation. The diffusion resistance layer 83 is made of a porous body that allows the gas to be measured to be brought into contact with the gas to be measured-side electrode 82A. Further, the diffusion resistance layer 83 is laminated on the surface of the sensor substrate 8 provided with the gas side electrode 82A to be measured, and the heater substrate 9 is laminated on the surface of the sensor substrate 8 provided with the reference gas side electrode 82B. is there.

As shown in FIG. 11, the heating element 92 in the heater substrate 9 has a heating part 901 formed by meandering conductors, and lead parts 902 made of conductors drawn from both ends of the heating part 901. The gas concentration detection element 7 has a heating region where the heat generating portion 901 and the sensor substrate 8 face each other on one end side L1 in the longitudinal direction L. The entire heating region is covered with a porous protective layer 75. The porous protective layer 75 is configured to allow the gas to be measured to permeate through a large number of fine pores P formed of ceramic particles.
As shown in FIGS. 10 and 12, the surface of the porous protective layer 75 is formed with a recess M that forms a bowl-shaped groove that is visible to the naked eye by a groove that is recessed toward the inside of the gas concentration detection element 7. Has been.

Hereinafter, the gas concentration detection element 7 of this example will be described in detail with reference to FIGS.
As shown in FIG. 9, the gas sensor 6 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, as shown in FIG. 10, the gas sensor 6 of the present example applies a voltage that generates a limit current characteristic between a pair of electrodes 82A and 82B provided on both surfaces of the solid electrolyte body 81, so Depending on the difference in oxygen concentration between the measurement gas in contact with the measurement gas side electrode 82A and the reference gas (atmosphere etc.) in contact with the reference gas side electrode 82B, which is the other electrode, between the pair of electrodes 82A, 82B It is possible to determine the air-fuel ratio in the engine by detecting the generated current.
Further, the sensor substrate 8 of the gas concentration detecting element 7 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 82A, B provided on both surfaces of the solid electrolyte body 81, and It has a one-cell structure that combines the function of a sensing cell that measures the oxygen concentration in the gas to be measured.

As shown in the figure, a diffusion resistance layer 83 for diffusing the gas to be measured and controlling the flow thereof is laminated on the surface of the solid electrolyte body 81 provided with the gas side electrode 82A to be measured. A shielding layer 84 is laminated on the surface of the diffusion resistance layer 83. The diffusion resistance layer 83 and the shielding layer 84 can be formed of alumina or the like. Further, the pair of electrodes 82A and 82B can be formed of platinum or the like.
The solid electrolyte body 81 is formed in a flat plate shape using a slurry in which ceramic powder made of an oxygen ion conductive solid electrolyte is dispersed in a solvent. The pair of electrodes 82 </ b> A and 82 </ b> B is formed by printing at positions facing each other on both surfaces of the solid electrolyte body 81. The ceramic body 91 is formed in a flat plate shape using a slurry in which an insulating material is dispersed in a solvent.

As shown in FIG. 10, the heater substrate 9 is laminated on the surface of the solid electrolyte body 81 provided with the reference gas side electrode 82B. The heater substrate 9 is formed by sandwiching a heating element 92 between one ceramic body 91A for forming the reference gas chamber 95 around the reference gas side electrode 82B and the other ceramic body 91B. The heating element 92 is formed by pattern-printing a conductor made of platinum or the like on any ceramic body 91.
Further, the pair of electrodes 82 </ b> A and B in the solid electrolyte body 81 are formed at positions facing a heat generating portion 901 (heating region) by the heat generating body 92.

As shown in FIG. 11, in the heater substrate 9, the heat generating portion 901 by the heat generating element 92 can be formed meandering in the longitudinal direction L of the gas concentration detecting element 7, and as shown in FIG. 13, the gas concentration detecting element 7 Can be formed by meandering in the horizontal direction W (direction perpendicular to the longitudinal direction L).
In the gas concentration detection element 2, a heating region where the heat generating portion 901 and the sensor substrate 8 in the heater substrate 9 face each other and a current-carrying region where the lead portion 902 and the sensor substrate 8 in the heater substrate 9 face each other are formed. ing.

As shown in FIG. 9, the rear end side portion (the other end L2 portion) 702 of the gas concentration detecting element 7 is fixed to a metal housing 61 via an insulator 64 having electrical insulation, The front end side portion (the end L1 portion) 701 of the concentration detection element 7 is covered with an element cover 62 fixed to the front end portion of the housing 61. The element cover 62 includes an inner cover 62A that covers the distal end portion 701 of the gas concentration detection element 7 and an outer cover 62B that covers the inner cover 62A. In the inner cover 62A and the outer cover 62B, measured gas inlets 63A and 63B are formed at different positions in the longitudinal direction L.
The rear end portion 702 of the gas concentration detection element 7 has a pair of electrodes 82A and 82B and a pair of conductors in the lead portion 902 of the heating element 92, and a conductive fitting 65 and a lead wire for electrically connecting the outside of the gas sensor 6. 66 is connected.

As shown in FIG. 10, the gas concentration detection element 7 of this 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 diffusion resistance layer 83, notched surfaces (C surface) 86 for guiding the gas to be measured to the diffusion resistance layer 83 are formed.
Further, the cross-sectional shape of the gas concentration detection element 7 has a substantially rectangular shape that is thin in the stacking direction D of the sensor substrate 8 and the heater substrate 9.

  In addition, on the surface of the gas concentration detecting element 7 (each surface of the sensor substrate 8, the heater substrate 9, the shielding layer 84, 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 concentration detecting element 7.

As shown in FIG. 10, the porous protective layer 75 has the largest film thickness (thickness) at the center portion of the surface in the stacking direction D of the sensor substrate 8 and the heater substrate 9 in the cross section orthogonal to the longitudinal direction L. The film thickness at all corners is the thinnest. The porous protective layer 75 of this example is the thickest part and is formed to a thickness of about 500 (μm).
The porous protective layer 75 is made of alumina particles (ceramic particles) having an average particle diameter of about 20 (μm), and the fine pores P formed by the alumina particles are formed with an opening diameter of about 20 (μm). .
The porous protective layer 75 is formed by laminating ceramic particles in a plurality of layers (two layers in this example) and improving the trapping performance of a plurality of types of poisonous substances, and ceramic particles 751B in the upper layer (porous protective layer). Can be formed larger than the average particle diameter of the ceramic particles 751A of the lower layer (fine particle porous layer) (see FIG. 16).

  The gas concentration detection element 7 of this example is formed by firing in a state where the sensor substrate 8, the heater substrate 9, the diffusion resistance layer 53, and the shielding layer 54 are laminated. The porous protective layer 75 is formed by immersing the gas concentration detecting element 7 in a slurry-like ceramic material containing a large number of ceramic particles in water as a solvent, so that the ceramic is formed on the surface of the gas concentration detecting element 7. After repeating the step of attaching the material and the step of drying the attached ceramic material, calcining (heat treatment) is performed.

Next, the recess M formed in the porous protective layer 75 will be described in detail.
As shown in FIGS. 10 and 11, the recess M of this example is formed on the surface in the stacking direction D in which the sensor substrate 8 and the heater substrate 9 are stacked. Further, the concave portion M in the porous protective layer 75 is formed in a portion facing the heating region of the gas concentration detection element 7. Further, in the cross section perpendicular to the direction in which the ridge-shaped groove is formed, the concave portion M is such that the width of the portion located on the surface side of the porous protective layer 75 is the width of the portion located on the inner side of the porous protective layer 75. It is formed in a groove shape having a pair of inclined side surfaces M1. It is considered that the inclined side surface M1 is not necessarily flat, and there is a portion having complicated unevenness.
In addition, the recess M may be formed in various shapes. When the recess M is formed as a ridge by one groove as shown in FIG. 11, the groove is formed as a ridge having a plurality of branches as shown in FIG. There are cases.

FIG. 14 is a diagram schematically illustrating the formation state of the recess M in the porous protective layer 5 as a cross section orthogonal to the direction in which the groove is formed.
As shown in the figure, in the recess M, the average width a between a pair of peak vertices T in a cross section perpendicular to the direction in which the groove is formed is in the range of 0.05 to 0.8 (mm). This average width a is determined as an average value of the width between a pair of peak vertices T at a plurality of locations in the formation direction of the recess M. In the recessed part M, the average depth b of the bottom part located between a pair of peak vertices T in the whole groove forming direction is in the range of 0.05 to 1 (mm). This average depth b is the depth from the lower peak apex T to the bottom of the pair of peak apexes T, and is determined as the average value of the depths of the bottoms at a plurality of locations in the formation direction of the recesses M. Moreover, the projection length projected on the longitudinal direction L of the recessed part M exists in the range of 1-15 (mm). The average film thickness (average thickness) d (mm) of the porous protective layer 75 corresponding to the bottom of the recess M is 0.02 (mm) or more. This average film thickness d is determined as an average value of the film thickness of the porous protective layer 75 corresponding to a plurality of locations in the formation direction of the recesses M.

In addition, the recess M can be specified following the swell motif of JIS B0631 (2003).
That is, the average width a can be represented by an average value AW of the motif length AWi (i = 1 to n) which is a curved portion sandwiched between two local mountains, and the average depth b is 2 It can be represented by the average value W of the motif depth HWi (i = 1 to n) which is the depth from the top of each mountain to the bottom of the valley.

  In the gas concentration detection element 7 of this example, the concave portion M is positively formed on the surface of the porous protective layer 75. Further, it was confirmed that the presence of the recesses M on the surface of the porous protective layer 75 can effectively improve the wet strength against water droplets without increasing the film thickness of the porous protective layer 75.

The reason why the wet strength can be improved due to the presence of the recess M is considered as follows.
That is, moisture in the gas to be measured that contacts the porous protective layer 75 is absorbed by a number of fine pores P on the pair of inclined side surfaces M1 of the recess M before reaching the surface of the gas concentration detecting element 7. In the porous protective layer 75, it can spread in the surface direction of the gas concentration detection element 7. Thereby, it is considered that the porous protective layer 75 can be provided with water absorption in the surface direction of the gas concentration detecting element 7, and the gas concentration detecting element 7 can hardly cause water cracking.

  In general, it was considered that the porous protective layer 75 should be formed uniformly. However, in the conventional gas concentration detecting element 7 having the porous protective layer 75 having no concave portion M, small water droplets that are in contact with the surface of the porous protective layer 75 during use heated to a high temperature Since the tension was small, the surface of the porous protective layer 75 did not get wet. These small water droplets roll so as to be repelled on the surface of the porous protective layer 75, and gather a lot to form large water droplets. Then, when the surface tension increased as these large water droplets, the surface of the porous protective layer 75 wets and spreads, and instantaneously penetrates into the porous protective layer 75. For this reason, it was found that the thermal shock due to the water was increased, and the gas concentration detecting element 7 was cracked by water.

  On the other hand, in the gas concentration detecting element 7 including the porous protective layer 75 in which the concave portion M is present, small water droplets that are in contact with the surface of the porous protective layer 75 during use when heated to a high temperature, It was found that the balance of surface tension was lost even with small water droplets. And a small water droplet can spread quickly in the surface direction in the porous protective layer 75, can evaporate, and can be dried immediately. For this reason, it was found that the thermal shock caused by water exposure can be reduced, and the water concentration cracking of the gas concentration detection element 7 can hardly occur.

In addition, according to the porous protective layer 75 of this example, the thermal shock caused by water can be reduced, so that the thickness of the porous protective layer 75 can be reduced, and the heat capacity of the entire gas concentration detecting element 7 is increased. This can be suppressed. Therefore, the gas concentration detecting element 7 can be activated early by the heating element 82, and the responsiveness can be improved.
Furthermore, since the concave portion M is formed in the porous protective layer 75, it is possible to reduce the generation of thermal stress when subjected to a thermal shock due to moisture, and to improve the durability of the porous protective layer 75. be able to.

  Therefore, according to the porous protective layer 75 of this example, the durability and responsiveness of the gas concentration detecting element 7 can be effectively improved.

Example 3
This example is an example showing a manufacturing method of the gas concentration detecting element 7 capable of effectively forming the porous protective layer 75 on the surface of the gas concentration detecting element 7 shown in the second embodiment.
Specifically, in this example, the following immersion process and drying process are repeated, and then a heat treatment process is performed to form the porous protective layer 75 on the surface of the gas concentration detection element 7.
In the dipping step, the tip side portion 701 (the portion where the heating region is formed) in the longitudinal direction L of the gas concentration detecting element 7 is dipped in a ceramic material containing ceramic particles in water as a solvent. Then, the gas concentration detecting element 7 is pulled up from the slurry-like ceramic material, and the ceramic material is adhered to the surface of the tip side portion 701 of the gas concentration detecting element 7. In addition, the gas concentration detection element 2 is immersed in the slurry-like ceramic material in a state where the gas concentration detection element 2 is attached to the insulator, and the tip side portion 701 protruding from the insulator.
The ceramic particles in the slurry-like ceramic material are alumina particles having an average particle size of 20 (μm). A slurry ceramic material having a viscosity of 500 mPa · s was employed. The average particle diameter and viscosity were measured in the same manner as in Example 1.

  Next, in the drying step, the ceramic material attached to the gas concentration detection element 7 is dried. In the drying process of this example, heated air is blown to dry. Then, in the drying process other than the final round, the drying is stopped when the moisture content of the ceramic material adhered to the gas concentration detecting element 7 is about 17 wt% or less (for example, 10 to 17 wt%). And after performing an immersion process again, when performing the drying process after the 2nd time, the recessed part M which comprises the bowl-shaped groove part visually recognizable with the naked eye can be generated on the surface of ceramic material. Thereby, in this example, in order to form the recessed part M, a special construction method is not required, but the recessed part M can be formed easily.

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 concentration detecting element 7 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 75 having a thin film thickness is formed by the first ceramic particles 751A, and the upper porous film having a thick film thickness by the second and third ceramic particles 751B. A protective layer 75 is formed (see FIG. 16).
In addition, the immersion process and drying process of the ceramic material after the second layer can be repeated 2 to 5 times.

In addition, after the immersion process and the drying process are repeatedly performed, the ceramic material on the surface of the gas concentration detection element 7 is dried until the water content becomes approximately 0 wt% as the main drying process.
Thereafter, in the heat treatment step, the ceramic material (ceramic particles) that has been almost completely dried is heat-treated to form a porous protective layer 75 on the surface of the gas concentration detecting element 7.
In addition, the base layer which baked simultaneously with the gas concentration detection element 7 can be provided in the surface of the gas concentration detection element 7 before performing an immersion process.

The reason why the concave portion M can be generated by performing the drying step is considered as follows.
That is, as shown in FIG. 15, when the upper ceramic material 750B is attached by dipping onto the lower ceramic material 750A with a low degree of drying, the longitudinal direction of the ceramic material 750 on the surface of the gas concentration detecting element 7 The film thickness distribution of L becomes large. Further, when the tip side portion 701 of the gas concentration detecting element 2 is immersed in a slurry-like ceramic material, the gas concentration detecting element 2 crosses the surface where the shielding layer 84 of the gas concentration detecting element 7 is laminated and the surface where the heater substrate 9 is laminated. The film thickness of the ceramic material 750 near the center of the surface is thicker than the film thickness of other portions. In the figure, moisture in the ceramic material is indicated by S.

  Then, as shown in FIG. 16, when the drying process is performed again, when the moisture remaining in the thick part of the lower ceramic material 750A evaporates, the upper and / or lower ceramic material 750 is removed. It is considered that the concave portion M is generated by attracting the ceramic particles 751 in FIG. Further, the contraction force generated when the water evaporates is indicated by an arrow F1, and the breaking force generated in the portion where the recess M is formed is indicated by an arrow F2.

Therefore, according to the manufacturing method of the gas concentration detecting element 7 of this example, the gas concentration detecting element 7 capable of effectively improving durability and responsiveness can be easily manufactured.
Also in this example, the configuration of the gas concentration detecting element 7 is the same as that of the first embodiment, and the same effects as those of the first embodiment can be obtained.

(Confirmation test)
In this confirmation test, in the same manner as in Example 3, a concave portion M was formed in the porous protective layer 75 on the surface of the gas concentration detecting element 7, and the average depth b and average width a of the concave portion M were changed. In some cases, it was confirmed how much water droplets caused the water concentration cracking of the gas concentration detecting element 7.
In FIG. 17, the horizontal axis represents the average depth b (mm) of the recess M, and the vertical axis represents the amount of water droplets (μl) in which the gas concentration detection element 7 caused water cracking. It is a graph which shows the relationship when changing (mm) as a parameter.
The average width a of the recesses M was changed to 0.8 mm, 0.5 mm, and 0.05 mm. Moreover, the relationship between the said average depth b and the amount of water droplets was measured also about the case where the recessed part M is not formed. The porous protective layer 75 was formed by immersing alumina particles, drying, and heat treatment. The projection length c of the concave portion M in the longitudinal direction L is 1 mm, and the concave portion M used for the measurement is a porous protective layer on the heater surface side (side where the heater substrate 9 is laminated on the sensor substrate 8). 75.

In the same figure, it was found that when the average depth b of the recesses M is larger than 0.05 mm, water cracking is less likely to occur when there is the recesses M than when there is no recesses M. .
From this result, it was found that the average depth b of the recesses M is preferably 0.05 mm or more. Moreover, it turned out that it is preferable to set the upper limit of the average depth b to 1 mm or less in order to suppress the increase in heat capacity.
Moreover, it turned out that it is preferable to make the average width a of the recessed part M into the range of 0.05-0.8 mm.

  FIG. 18 is a graph showing the difference in weight of the porous protective layer 75 when there is no recess M (comparative product) and when there is a recess M (invention product). As shown in the figure, it was found that the weight of the porous protective layer 75 can be reduced by about 6% when the recess M is present, compared to the case where the recess M is not present. Therefore, it was found that the heat capacity of the porous protective layer 75 can be reduced by forming the recess M in the porous protective layer 75.

  FIG. 19 is a graph showing the difference in step response of the gas concentration detection element 7 when there is no recess M (comparative product) and when there is a recess M (invention product). As shown in the figure, it was found that the step response of the gas concentration detecting element 7 can be shortened by about 8% when there is a recess M compared to when there is no recess M. Therefore, it was found that the time for heating and activating the gas concentration detecting element 7 can be shortened by forming the recess M in the porous protective layer 75.

These are the cross-sectional schematic diagrams which showed the principal part of the gas concentration detection element in Example 1, and expanded one part. (A), (b) is the dimension definition of the opening part which is the principal part of this invention, and its theoretical explanatory drawing. These are the characteristic views which show the experimental value and calculated value of the variable i regarding the depth direction of the opening part which are the principal parts of this invention. FIG. 2 is a partially cutaway cross-sectional view showing the overall configuration of the gas sensor in Example 1. (A), (b), (c) is a characteristic view which shows the specific effect in Example 1 with a comparative example. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective developed view showing a configuration of a gas concentration detection element used for a gas sensor in Example 1. The schematic diagram which shows the formation process of a fine particle porous protective layer later on in order of (a)-(c). The schematic diagram which shows the formation process of the coarse particle porous protective layer which is the principal part of this invention later on in order of (a)-(c). Sectional explanatory drawing which shows the gas sensor which uses the gas concentration detection element in Example 2. FIG. Sectional explanatory drawing which shows typically the cross section of the heating area | region of the gas concentration detection element in Example 2. FIG. FIG. 6 is an explanatory diagram schematically showing a heating region formation state in the gas concentration detection element in Example 2. FIG. 4 is an explanatory diagram schematically showing a formation state of a recess in a porous protective layer of a gas concentration detection element in Example 2. Explanatory drawing which shows typically the formation state of the heating area | region in the other gas concentration detection element in Example 2. FIG. Cross-sectional explanatory drawing which shows typically the formation state of the recessed part in the porous protective layer in Example 2 as a cross section orthogonal to the direction which forms a groove | channel. Sectional explanatory drawing which shows typically the state which made the upper-layer ceramic material adhere on the lower-layer ceramic material with a little dry degree in Example 3. FIG. Sectional explanatory drawing which shows the state which produces a recessed part in the ceramic material in the surface of the gas concentration detection element in Example 3. FIG. The graph which shows the relationship between both by taking the average depth b (mm) of a recessed part on a horizontal axis | shaft in a confirmation test, and taking the amount (microliter) of water droplets in which the gas concentration detection element caused water cracking on the vertical axis. The graph which shows the difference in the weight of a porous protective layer about the case where there is no recessed part and the case where there is a recessed part in a confirmation test. The graph which shows the difference in the step responsiveness of a gas concentration detection element about the case where there is no recessed part and the case where there is a recessed part in a confirmation test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Gas concentration detection element 100 Solid electrolyte layer 110 Measurement electrode layer 120 Reference electrode layer 130 Porous diffusion resistance layer 140 Reference gas chamber 141 Reference gas chamber formation layer 150 Insulating substrate 151 Heating element 170 Porous protective layer P _MIC pore P _MAC Opening (concave)

Claims (22)

In the gas concentration detection element that detects the concentration of the specific gas component in the gas to be measured,
The gas concentration detection element comprises a porous protective layer covering the surface of the gas concentration detection element exposed to the gas to be measured,
A gas concentration detecting element characterized in that the surface of the porous protective layer is recessed toward the element side, and at least one or more concave portions are provided in the surface of the porous protective layer.   The gas concentration detection element according to claim 1, wherein the opening of the recess is visible with the naked eye.   3. The gas concentration detecting element according to claim 1, wherein the opening of the recess has an equivalent circle diameter of 0.1 mm or more. 3. The concave portion according to claim 1, wherein one side of the minimum square S _Q1 circumscribing the opening of the concave portion is a (mm) and the depth D _{P of the} concave portion is b (mm). A gas concentration detecting element formed in a range satisfying the above relationship.
i = (b / 0.008 + 1), {(1−0.27 / a) ² } ⁱ ≦ 0.0027 (Equation 1) 5. The gas concentration according to claim 1, wherein when the thickness T ₃ of the porous protective layer in the formation portion of the recess is c (μm), the relationship of Formula 2 is satisfied. Detection element.
c ≧ 25 Formula 2 6. The gas concentration detecting element according to claim 1, wherein a relationship of Formula 3 is satisfied when one side of the minimum square S _Q1 circumscribing the opening of the concave portion is a (mm). .
0.27 ≦ a ≦ 1.8 Formula 3 7. The gas concentration detection element according to claim 1, wherein a plurality of the recesses are provided, and the relationship of Formula 4 is satisfied when a distance L _p between the recesses is d (mm).
d ≧ 1.8 Formula 4   8. The gas concentration detection element according to claim 1, wherein the porous protective layer is formed with a bowl-shaped groove extending continuously from the concave portion. 9.   In Claim 8, average width a between a pair of mountain peaks in a section orthogonal to the direction which forms the above-mentioned bowl-like groove is 0.05-0.8 (mm), and said bowl-like groove A gas concentration detecting element, wherein an average depth b of a bottom portion located between a pair of peak vertices in a whole direction in which the distance is formed is 0.05 to 1 (mm).   10. The gas concentration detection element according to claim 1, wherein the gas concentration detection element is formed on at least an oxygen ion conductive solid electrolyte layer formed in a flat plate shape and one surface of the solid electrolyte layer. A measurement electrode layer in contact with the measurement gas, a porous diffusion resistance layer that is formed on the measurement electrode layer side and transmits the gas to be measured, and a reference electrode that is formed on the other surface of the solid electrolyte layer and is in contact with the reference gas A laminate formed by laminating a layer, a reference gas chamber forming layer having a reference gas chamber that is formed on the reference electrode layer side and that introduces a reference gas, and an insulating base that has a heating element that generates heat when energized. A gas concentration detecting element characterized by being a gas concentration detecting element of the type.   10. The gas concentration detection element according to claim 1, wherein the gas concentration detection element includes a sensor substrate provided with a pair of electrodes on both surfaces of a solid electrolyte body having oxygen ion conductivity, and a ceramic body having electrical insulation. A heater substrate provided with a heating element that generates heat when energized, and a diffusion resistance layer made of a porous body that transmits a gas to be measured that is in contact with one of the pair of electrodes. A gas concentration detecting element comprising a resistance layer laminated on one surface of the sensor substrate and a heater substrate laminated on the other surface of the sensor substrate. . In claim 11, 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 concentration detecting element has a heating region where the heat generating portion and the sensor substrate face each other on one side in the longitudinal direction, and the entire heating region is covered with the porous protective layer. A gas concentration detecting element.   13. The gas concentration detecting element according to claim 12, wherein at least a part of the concave portion is formed at a portion facing the heating region.   14. The gas concentration according to claim 11, wherein the recess is formed at one or a plurality of locations on a surface in a stacking direction in which the sensor substrate and the heater substrate are stacked. Detection element.   10. The cup-type oxygen ion conductive solid electrolyte body according to claim 1, wherein one of the gas concentration detecting elements is closed and a reference gas chamber is provided therein, and the solid electrolyte. A measuring electrode provided on the outer surface of the body and in contact with the gas to be measured, and a reference electrode provided on the inner surface of the solid electrolyte body. A gas concentration detection element comprising a cup-type gas concentration detection element in which an insulating substrate is inserted and disposed. In the method for manufacturing the gas concentration detection element according to any one of claims 1 to 15,
A porous protective layer forming step in which the gas concentration detecting element is immersed in a slurry in which heat-resistant ceramic particles are dispersed, and this is dried and calcined to form a porous protective layer covering the surface of the gas concentration detecting element A method for manufacturing a gas concentration detecting element, comprising:   17. The method according to claim 16, further comprising the step of forming the recesses on the surface of the porous protective layer by dispersing a precursor composed of bubbles, organic particles or an emulsion that can be burned down during calcination, in the slurry. A method for manufacturing a gas concentration detecting element. In the method for manufacturing the gas concentration detection element according to any one of claims 1 to 15,
A dipping step of immersing the gas concentration detection element in a slurry containing ceramic particles in a solvent and a drying step of drying the ceramic material adhering to the surface of the gas concentration detection element are repeated, and then dried. In performing the heat treatment step of forming a porous protective layer on the surface of the gas concentration detecting element by heat-treating the ceramic material, the porous protective layer is formed.
A manufacturing method of a gas concentration detecting element, wherein the concave portion is generated on the surface of the ceramic material when performing the second and subsequent drying steps.   The method for manufacturing a gas concentration detecting element according to any one of claims 16 to 18, wherein the ceramic particles are made of alumina particles having an average particle size of 25 (µm) or less.   20. The method of manufacturing a gas concentration detecting element according to claim 16, wherein the porous protective layer is formed using the slurry having a viscosity of 200 to 1200 (mPa · s). .   The gas concentration detection according to any one of claims 16 to 19, wherein the gas concentration is detected in a slurry for forming a fine particle porous layer containing ceramic particles having an average particle diameter of 1 to 9 (µm) before the formation of the porous protective layer. After the element is immersed and dried, the porous protective layer forming slurry containing ceramic particles having an average particle size of 13 to 25 (μm) is used as the porous protective layer forming slurry. A method for producing a gas concentration detecting element, comprising forming the protective layer to form the porous protective layer on the fine particle porous protective layer.   The method for manufacturing a gas concentration detecting element according to claim 21, wherein the fine particle porous layer forming slurry has a viscosity of 11 to 600 (mPa · s).

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