JP6957410B2 - Gas sensor element and gas sensor manufacturing method - Google Patents

Description

The present invention relates to a gas sensor element that forms a porous protective layer around a detection portion of the gas sensor element, and a method for manufacturing the gas sensor.

Oxygen sensors and air-fuel ratio sensors that detect the oxygen concentration in the gas to be measured (intake gas and exhaust gas) are known as gas sensors that improve the fuel efficiency of internal combustion engines such as automobile engines and control combustion.
As shown in FIG. 3, such a gas sensor has a plate-shaped gas sensor element 100 extending in the axial direction and having a detection unit 10 for detecting a specific gas component in the gas to be measured on its tip side. Is commonly used. Further, in order to prevent water droplets in the exhaust gas from coming into contact with the detection unit 10 and applying a thermal shock, a porous protective layer 20 is formed around the detection unit 10.
Further, in order to reduce the heat capacity of the porous protective layer 20 on the tip side of the detection unit 10 and improve the responsiveness to the temperature change of the gas to be measured, the corner portion 20R of the porous protective layer 20 on the tip side is chamfered. It is required to have a uniform thickness with the part of.

Conventionally, a spray method for spraying a slurry containing the material of the porous protective layer, a dip method for immersing the detection unit in the slurry, or the like has been used for the porous protective layer. There is unevenness.
Therefore, a technique for controlling the film thickness by accommodating a detection unit in a molding die and injecting a slurry has been developed (Patent Document 1).
On the other hand, there is known a technique of putting raw material powder into a rubber mold and press-molding it with a mandrel under hydrostatic pressure (Patent Document 2).

Japanese Unexamined Patent Publication No. 2013-217733 (Fig. 2) Japanese Unexamined Patent Publication No. 6-142900

By the way, in the case of the method of Patent Document 1, in order to inject the slurry into the molding mold, it is necessary to increase the ratio of the liquid component (volatile component in drying / firing) in the slurry. Therefore, when the slurry dries, cracks are likely to occur due to shrinkage, and there is a problem that the strength of the porous protective layer is weakened.
Therefore, the present inventors applied the technique of Patent Document 2 and installed the gas sensor element 100 in advance inside the rubber mold 500 as shown in the cross-sectional view 8, and inside the rubber mold 500 around the gas sensor element 100. An attempt was made to put the powder raw material 20x of the porous protective layer into the cavity and apply a press pressure P500 to perform press molding.
Then, as shown in FIG. 9, in order to form the above-mentioned corner portion 20R, a recess 510r is provided in the push rubber 510 that presses the tip side of the gas sensor element 100 from above the rubber mold 500, and the taper 510t that becomes the corner portion 20R is formed. However, it was found that the powder raw material 20x in the cavity was not sufficiently solidified near the taper 510t. This is because the hardness of the push rubber 510 is higher than the hardness of the rubber mold 500, so that when the lateral thickness t1 of the push rubber 510 becomes thicker near the taper 510t, the press pressure P500 is sufficient for the powder raw material 20x near the taper 510t. It is thought that it does not hang.

Therefore, an object of the present invention is to provide a gas sensor element and a method for manufacturing a gas sensor capable of forming a porous protective layer having chamfered corners on the tip side reliably and at low cost.

In order to solve the above problems, the method for manufacturing a gas sensor element of the present invention extends in the axial direction and has a plate-like or tubular shape having a detection unit for detecting a specific gas component in the gas to be measured on its tip side. In the method for manufacturing a gas sensor element that forms a porous protective layer around the detection unit with respect to the gas sensor element, a holding step of holding the gas sensor element in a cavity of a rubber mold so that the detection unit is exposed, and the above-mentioned The raw material powder of the porous protective layer is charged into the cavity through a charging hole that communicates with the cavity and faces the tip end side of the detection unit, and the raw material powder is pressed by a pressing rubber that advances and retreats in the charging hole. It has a first pressing step and a second pressing step of isotropically pressing the outside of the rubber mold to form the porous protective layer, and the durometer hardness of the pressed rubber is higher than the durometer hardness of the rubber mold. High, the inner wall of the cavity is provided with a tapered surface that extends from the input hole toward the cavity, and in the holding step, the corner portion of the tip of the detection unit is held so as to face the tapered surface.

According to this method of manufacturing a gas sensor element, the corner portion of the tip of the detection portion is held facing the tapered surface provided in the cavity, the raw material powder is pressed with a pressing rubber, and then the outside of the rubber mold is subjected to isotropic pressure. Press to form a porous protective layer.
As a result, even if the hardness of the push rubber is higher than the hardness of the rubber mold, the lateral thickness of the push rubber does not increase near the tapered surface, and the tapered surface is composed of a rubber mold softer than the push rubber. Therefore, the pressure at the time of isotropic pressure pressing is sufficiently applied to the raw material powder at the corner of the detection portion near the tapered surface, and a porous protective layer with the corner at the tip side chamfered is formed reliably and at low cost. Further, since the raw material powder is compressed to form the porous protective layer, it is not necessary to make a slurry, so that the strength of the porous protective layer is also improved.
Furthermore, by changing the press pressure, the strength and porosity of the porous protective layer can be changed in a wider range than in the conventional method.
When isotropic pressure pressing is performed using a rubber mold for press molding, the press pressure is evenly (isotropically) applied to the inside from the outside of the rubber mold, so that there is no uneven compression of the raw material powder and the porosity is protected. There is an advantage that the thickness and characteristics of the layer become more uniform.

In the method for manufacturing a gas sensor element of the present invention, it is preferable that the maximum diameter D1 of the input hole satisfies the relationship of (D2 × 0.5) ≦ D1 ≦ D2 with respect to the maximum diameter D2 of the cavity.
According to this method of manufacturing the gas sensor element, the raw material powder can be smoothly supplied and pressed.

In the method for manufacturing a gas sensor element of the present invention, the pressing surface of the pressing rubber may be recessed.
According to this method of manufacturing the gas sensor element, the raw material powder can be more reliably compressed by the pressing rubber in the first pressing step.

In the method for manufacturing a gas sensor element of the present invention, the taper angle of the tapered surface may be 15 to 45 degrees.
According to this method of manufacturing the gas sensor element, the corner portion on the tip side of the porous protective layer can be chamfered more reliably, and the heat capacity on the tip side of the porous protective layer can be surely reduced.

In the method for manufacturing a gas sensor of the present invention, in the method for manufacturing a gas sensor in which a main metal fitting is attached to the gas sensor element, the gas sensor element manufactured by the method for manufacturing the gas sensor element is used as the gas sensor element.

According to the present invention, the gas sensor element and the porous protective layer in which the corners on the tip side of the gas sensor are chamfered can be formed reliably and at low cost.

It is a schematic perspective view of the gas sensor element manufactured by the manufacturing method of the gas sensor element which concerns on embodiment of this invention. It is a figure which follows the AA line of FIG. It is sectional drawing which shows the chamfered corner part on the tip side of the porous protective layer. It is sectional drawing along the vertical direction which shows an example of the press molding machine used in the manufacturing method of the gas sensor element which concerns on embodiment of this invention. It is a partially enlarged view of FIG. It is sectional drawing which follows the horizontal direction of the press molding machine of FIG. It is a process drawing which shows the manufacturing method of a gas sensor element. It is sectional drawing which shows the method of forming a porous protective layer using a conventional rubber mold. It is sectional drawing along the vertical direction which shows the method of forming a porous protective layer using a conventional rubber mold.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a schematic perspective view of a gas sensor element 100 manufactured by the method for manufacturing a gas sensor element according to an embodiment of the present invention, and FIG. 2 is a view taken along the line AA of FIG.
As shown in FIG. 1, the gas sensor element 100 is formed in a plate shape extending in the axis O direction, has a detection unit 10 for detecting a specific gas component in the gas to be measured on the tip side, and is around the detection unit 10. A porous protective layer 20 is formed on the surface. The gas sensor element 100 or the like is assembled to the gas sensor by a main metal fitting or the like (not shown).
The main metal fitting is formed in a substantially cylindrical shape having a through hole penetrating in the axial direction, the detection unit 100 of the gas sensor element 100 is arranged on the tip side of the tip of the through hole, and the rear end side of the gas sensor element 100 is arranged. It is configured to hold the gas sensor element 100 inserted through the through hole in a state of being arranged on the rear end side of the through hole 137.

Further, as shown in FIG. 2, the gas sensor element 100 includes a detection element unit 300 and a heater unit 200 laminated on the detection element unit 300.
The detection element unit 300 includes an oxygen concentration detection cell 130 and an oxygen pump cell 140, and realizes a so-called all-region air-fuel ratio sensor that detects the air-fuel ratio from the oxygen concentration in the gas to be measured. The oxygen concentration detection cell 130 is formed of a first solid electrolyte body 105 and a first electrode 104 and a second electrode 106 formed on both sides of the first solid electrolyte 105. On the other hand, the oxygen pump cell 140 is formed of a second solid electrolyte body 109 and a third electrode 108 and a fourth electrode 110 formed on both sides of the second solid electrolyte body 109.

A measurement chamber 107c is formed between the oxygen pump cell 140 and the oxygen concentration detection cell 130, and the second electrode 106 and the third electrode 108 face the measurement chamber 107c, respectively. The measurement chamber 107c communicates with the outside in the width direction of the element, and a diffusion resistance portion 115 that realizes gas diffusion between the outside and the measurement chamber 107c under a predetermined rate-determining condition is arranged in the communication portion. ing.
Further, the outer surface of the fourth electrode 110 is covered with a porous electrode protection portion 113a, and the electrode protection portion 113a is exposed on the outer surface of the element. As a result, oxygen is taken in from the outside or pumped out from the outside through the electrode protection portion 113a and the porous protective layer 20 from the fourth electrode 110.

The porous protective layer 20 is formed so as to cover the outer surface of the laminate of the detection element portion 300 and the heater portion 200. That is, the porous protective layer 20 is provided so as to cover the entire circumference of the detection unit 10 provided at the tip end side portion of the gas sensor element 100.
The detection unit 10 refers to the solid electrolytes 105 and 109 sandwiched between the electrodes 104 to 110 and the electrodes 104 to 110 of the detection element unit 300, and further to the measurement chamber 107c. Therefore, it is sufficient that the porous protective layer 20 is covered from the rearmost end of the detection unit 10 in the axis O direction to the rear end side.
Further, the porous protective layer 20 may cover the entire circumference of the detection unit 10 and may cover the detection element unit 300 provided with the detection unit 10, but the detection element unit 300 is a heater as in the above embodiment. When the laminated body is formed with the portion 200, the porous protective layer 20 covers the laminated body (the tip end side portion of the gas sensor element 100) including the detection element portion 300.
On the other hand, when the gas sensor element 100 does not include the heater unit 200, the porous protective layer 20 may cover the entire circumference of the detection element unit 300 (detection unit 10).

As described above, as shown in FIG. 3, in order to reduce the heat capacity of the porous protective layer 20 on the tip side of the detection unit 10 and improve the responsiveness to the temperature change of the gas to be measured, the porosity on the tip side is improved. The corner portion 20R of the protective layer 20 is chamfered to have a uniform thickness with other portions.

Next, a method of manufacturing the gas sensor element according to the embodiment of the present invention will be described.
FIG. 4 is a cross-sectional view taken along the vertical direction showing an example of a press molding machine used in the method for manufacturing a gas sensor element according to an embodiment of the present invention, FIG. 5 is a partially enlarged view of FIG. 4, and FIG. 6 is a horizontal view of the press molding machine. A cross-sectional view taken along the direction, FIG. 7 is a process diagram showing a method of manufacturing a gas sensor element.
As shown in FIG. 4, the press molding machine is a cold isotropic press (CIP) machine provided with a rubber mold (rubber mold) 204, and the rubber mold 204 is installed in the water tank 202 and is in the water tank 202. Press molding is performed by isotropic pressure (hydrostatic pressure) P1.

As shown in FIG. 6, in the rubber mold 204, the insertion hole 204h forming the inner hole has a cylindrical shape with a rectangular cross section, and the detection unit 10 of the gas sensor element 100 is arranged in the insertion hole 204h so as to be separated from the insertion hole 204h. After the raw material powder 20x of the porous protective layer is put into the void (cavity) between the detection unit 10 and the detection unit 10, the rubber mold 204 and the raw material powder 20x are obtained by applying the hydrostatic pressure P1 to the rubber mold 204 from the outside. It is compressed and solidified into the shape of the porous protective layer 20 to be formed. Then, the gas sensor element 100 is taken out from the rubber mold 204, and the porous protective layer 20 is fired.

Here, as shown in FIG. 4, the upper pin holder 208 for holding the push rubber 208a is inserted into the upper surface side opening of the rubber mold 204, and the hydraulic piston 206 comes into contact with the upper pin holder 208. Then, the hydraulic piston 206 is also lowered by the hydraulic pressure P3 to press the upper pin holder 208 downward, and the raw material powder 20x in the rubber mold 204 is compressed.
On the other hand, the lower pin holder 210 has an inner hole 210h having a rectangular cross section slightly larger than the cross section of the gas sensor element 100 along the axial direction, and the lower pin holder 210h accommodates and holds the gas sensor element 100 in the inner hole 210h. The detection unit 10 of the gas sensor element 100 projects upward from the tip (upper side) of the 210. Further, an annular rubber seal 210a is interposed between the tip of the lower pin holder 210 and the gap between the gas sensor element 100.

Then, the lower pin holder 210 is inserted through the opening on the lower surface side of the rubber mold 204, and the upper and lower surfaces of the rubber mold 204 are liquid-tightly sealed by the push rubber 208a and the rubber seal 210a.
The cavity is composed of an insertion hole 204h of the rubber mold 204, a detection unit 10, a gap surrounded by the push rubber 208a and the rubber seal 210a.

The raw material powder 20x contains a component of the porous protective layer 20 (for example, a ceramic powder such as alumina) and a binder such as PVA, and further contains burnable particles, a lubricant (release agent), and a dispersant, if necessary. Etc. can be contained.

Here, as shown in FIG. 4, the lower pin holder 210 has a flange portion 210f formed on the lower surface thereof, a shoulder portion 210s that rises upward from the flange portion 210f and further narrows upward, and further shoulder portion 210s. It has a shape that rises upward from.
Then, the portion of the lower pin holder 210 above the shoulder portion 210s is inserted into the insertion hole 204h of the rubber mold 204. Further, the flange portion 210f is placed on the base 300 and can slide in the horizontal (left and right) direction. As a result, the lower pin holder 210 is movable with respect to the rubber mold 204.

Here, as shown in the enlarged view 5, the rubber 208a advances and retreats in the insertion hole 204h2 forming the opening on the upper surface side of the rubber mold 204. Further, the inner wall of the cavity (rubber mold 204) is provided with a tapered surface 204t extending from the input hole 204h2 toward the cavity, and the corner portion 100R at the tip of the gas sensor element 100 (detection unit 10) is made to face the tapered surface 204t. The gas sensor element 100 is arranged.
Further, the durometer hardness of the push rubber 208a is higher than the durometer hardness of the rubber mold 204. As a result, the raw material powder 20x in the cavity is reliably compressed by the pressing rubber 208a, and the rubber mold 204, which is softer than the pressing rubber 208a, is easily compressed by the hydrostatic pressure P1 of the isotropic press.

In the present embodiment, the maximum diameter D1 of the input hole 204h2 satisfies the relationship of (D2 × 0.5) ≦ D1 ≦ D2 with respect to the maximum diameter D2 of the cavity.
Further, the pressing surface 208f of the push rubber 208a is recessed, and the taper angle θ of the tapered surface 204 is 15 to 45 degrees.

Next, with reference to FIG. 7, each step of the method for manufacturing the gas sensor element according to the embodiment of the present invention will be described.
First, the gas sensor element 100 is held in the lower pin holder 210 so that the detection unit 10 is exposed (FIG. 7A).
Then, the lower pin holder 210 holding the gas sensor element 100 is inserted into the lower surface side opening of the rubber mold 204 (FIG. 7 (b): holding step). Here, the gas sensor element 100 (lower pin holder 210) is inserted so that the detection portion 10 protruding above the lower pin holder 210 is arranged in the cavity of the rubber mold 204. Further, as shown in FIG. 5, the corner portion 100R at the tip of the gas sensor element 100 (detection unit 10) is made to face the tapered surface 204t. Further, a portion of the lower pin holder 210 above the shoulder portion 210s is inserted into the insertion hole 204h of the rubber mold 204, and the lower pin holder 210 is moved with respect to the rubber mold 204.

Next, the raw material powder 20x of the porous protective layer is charged into the cavity (the gap surrounded by the insertion hole 204h, the detection unit 10 and the rubber seal 210a, and the upper part is open) from the charging hole 204h2 of the rubber mold 204. Further, the upper pin holder 208 is inserted into the insertion hole 204h2 of the rubber mold 204, and the hydraulic piston 206 is arranged above the upper pin holder 208 (FIG. 7 (c)). As a result, the rubber 208a is closed by pushing the upper opening of the cavity, and the cavity is completed.

Then, by pressing the upper pin holder 208 downward from the hydraulic piston 206 with the hydraulic pressure P3, the raw material powder 20x in the cavity is press-molded (FIG. 7 (d): first press step).
Next, a hydrostatic pressure P1 is applied to the rubber mold 204 from the outside and the rubber mold 204 is isotropically pressed to form the porous protective layer 20 (FIG. 7 (d): second pressing step).
Finally, the lower pin holder 210 and the upper pin holder 208 are taken out from the rubber mold 204, and the gas sensor element 100 is taken out from the lower pin holder 210 (FIG. 7 (e)).

According to the method for manufacturing a gas sensor element according to the embodiment of the present invention, as shown in FIG. 5, the corner portion 100R at the tip of the detection unit 10 is held facing the tapered surface 204t provided in the cavity, and the push rubber is pressed. After pressing the raw material powder 20x with 208a, the outside of the rubber mold 204 is isotropically pressed to form the porous protective layer 20.
As a result, even if the hardness of the push rubber 208a is higher than the hardness of the rubber mold 204, the lateral thickness of the push rubber 208a does not increase near the tapered surface 204t, and the tapered surface 204t is softer than the push rubber 208a. Consists of. Therefore, during the isotropic pressure press, the hydrostatic pressure P1 is sufficiently applied to the raw material powder 20x of the corner portion 100R of the detection portion 10 near the tapered surface 204t, and the corner portion 20R on the tip side is chamfered. Can be formed reliably and at low cost

Further, since the raw material powder 20x is compressed to form the porous protective layer 20, it is not necessary to make a slurry, so that the strength of the porous protective layer 20 is also improved.
Further, by changing the press pressure, the strength and porosity of the porous protective layer 20 can be changed in a wider range than in the conventional method.
When isotropic pressure pressing is performed using the rubber mold 204 for press molding, as shown in FIG. 6, the hydrostatic pressure P1 which is the pressing pressure is evenly (isotropically) applied to the inside from the outside of the rubber mold 204. Therefore, there is an advantage that the thickness and characteristics of the porous protective layer 20 become more uniform without uneven compression of the raw material powder 20x.

Further, if the relationship of (D2 × 0.5) ≦ D1 ≦ D2 is satisfied, the raw material powder can be smoothly supplied and pressed. If D1 <(D2 × 0.5), the gap between the gas sensor element 100 and the rubber mold 204 becomes too narrow, and it may be difficult to smoothly supply the raw material powder 20x into the rubber mold 204. Further, when D1> D2, the diameter of the push rubber 208a exceeds the outer dimension of the cavity, so that the press pressure may not be sufficiently transmitted during pressing in the axis O direction.
Further, when the pressing surface 208f of the pressing rubber 208a is recessed, the raw material powder 20x can be more reliably compressed by the pressing rubber 208a in the first pressing step.
When the taper angle θ of the tapered surface 204 is 15 to 45 degrees, the corner portion 20R on the tip side of the porous protective layer 20 is chamfered more reliably to ensure the heat capacity on the tip side of the porous protective layer 20. Can be reduced to.

The present invention is not limited to each of the above embodiments, and various modifications can be made. For example, in the above embodiment, the porous protective layer is one layer, but it may be two or more layers. In this case, the method for producing a gas sensor element according to the embodiment of the present invention may be applied to at least the outermost porous protective layer, but the present invention may be applied to two or more or all of the porous protective layers of the present invention. Of course, the method for manufacturing the gas sensor element according to the embodiment may be applied. When the number of porous protective layers is two or more, the material, thickness, porosity, etc. of each layer may be different.
The thickness of the porous protective layer per layer is not limited, but can be, for example, 100 to 1000 μm.

Further, in the present embodiment, the air-fuel ratio sensor in all regions has been described as an example, but it can be similarly applied to other oxygen sensor elements, NOx sensor elements, HC sensor elements and the like. The gas sensor element may be cylindrical.

10 Detection part 100R Corner of the tip of the detection part 20 Porous protective layer 20x Raw material powder of porous protective layer 100 Gas sensor element 204 Rubber mold 204h2 Rubber mold input hole 204t Tapered surface 208a Pressing rubber 208f Pressing rubber pressing surface O axis θ taper angle

Claims (5)

For a plate-shaped or tubular gas sensor element that extends in the axial direction and has a detection unit for detecting a specific gas component in the gas to be measured on its tip side, a porous protective layer is formed around the detection unit. In the manufacturing method of the gas sensor element
A holding step of holding the gas sensor element in the cavity of the rubber mold so that the detection portion is exposed, and
The raw material powder of the porous protective layer is charged into the cavity through a charging hole that communicates with the cavity and faces the tip end side of the detection unit, and the raw material powder is pressed by a pressing rubber that advances and retreats in the charging hole. 1st press process and
It has a second pressing step of forming the porous protective layer by isotropically pressing the outside of the rubber mold.
The durometer hardness of the pressed rubber is higher than the durometer hardness of the rubber mold.
The inner wall of the cavity is provided with a tapered surface that extends from the input hole toward the cavity, and a gas sensor element that holds the corner of the tip of the detection unit facing the tapered surface in the holding step is manufactured. Method. The method for manufacturing a gas sensor element according to claim 1, wherein the maximum diameter D1 of the input hole satisfies the relationship of (D2 × 0.5) ≦ D1 ≦ D2 with respect to the maximum diameter D2 of the cavity. The method for manufacturing a gas sensor element according to claim 1 or 2, wherein the pressing surface of the push rubber is recessed. The method for manufacturing a gas sensor element according to any one of claims 1 to 3, wherein the taper angle of the tapered surface is 15 to 45 degrees. In the method of manufacturing a gas sensor in which the main metal fitting is attached to the gas sensor element
A method for manufacturing a gas sensor using a gas sensor element manufactured by the method for manufacturing a gas sensor element according to any one of claims 1 to 4 as the gas sensor element.

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