JP2019095261A - Gas sensor elements and gas sensor - Google Patents

Abstract

To provide a gas sensor element and a gas sensor in which damaging is hard to occur even when used in a low temperature environment in the gas sensor element having an insulating protective layer having a porous portion.SOLUTION: The cell includes a solid electrolyte layer and a first electrode and a second electrode, and an insulating protective layer includes a porous portion 99 and a dense portion. The gas sensor element can reduce the area of a porous portion exposed to the outer surface of the insulating protective layer by a cross-sectional area of the porous portion taking a configuration smaller than the cross-sectional area of the first electrode 85, and it is possible to suppress the damage by stress due to thermal shock being reduced and to suppress the damage of the insulating protective layer due to a volume change of the moisture contained in the porous portion. By the electrode abutment portion 92 taking a configuration in contact with the first electrode covering the first entire electrode, the first electrode can pass the gas between an electrode abutment portion in a region other than an abutment surface with the solid electrolyte layer.SELECTED DRAWING: Figure 5

Description

  The present disclosure relates to a gas sensor element and a gas sensor.

There is known a gas sensor provided with a gas sensor element for detecting a specific gas contained in a gas to be measured.
The gas sensor is provided, for example, in the exhaust pipe of an internal combustion engine such as a car and is used for detecting the concentration of a specific component (oxygen, NOx, etc.) in the exhaust gas of the internal combustion engine. As a gas sensor element, there is a thing provided with a cell which has a solid electrolyte body and an electrode, and an insulation protection layer laminated to a cell. The insulating and protective layer may be configured to include a porous portion provided at the formation position of the electrode and a dense portion surrounding the periphery of the porous portion.

  Such a gas sensor element is configured such that the porous portion covers the electrode of the cell. The porous portion protects the electrode by preventing foreign matter such as soot from coming into direct contact with the electrode while permitting passage of gas between the outside of the gas sensor element and the electrode.

JP, 2016-080684, A

  However, in the above-described gas sensor element, if the temperature is lowered to below the freezing point in the state where water is contained in the porous portion, the gas sensor element (in particular, the dense portion of the insulating protective layer) is damaged (cracked) Etc.).

  That is, when the installation location of the gas sensor is an environment with a lot of moisture, moisture may be contained in the porous part, and the volume change of the moisture may occur due to the temperature decrease, and the gas sensor element may be damaged. For example, in a low temperature environment such as winter, condensed water is likely to be generated during stoppage of the internal combustion engine in the exhaust pipe of the internal combustion engine, and the condensed water reaches the gas sensor together with the exhaust gas at startup of the internal combustion engine. The part may contain moisture.

  On the other hand, a method of reducing the stress by forming the porous portion smaller can be considered, but in the porous portion formed smaller, the amount of gas which can pass through per unit time becomes smaller, so that the cells (specifically, The amount of gas that can be transferred between the electrode and the porous material is reduced, which may reduce the accuracy of gas detection.

  In this case, by increasing the voltage applied to the cell (specifically, the electrode) to pump the gas, there is a possibility that the decrease in the amount of gas that can be delivered can be suppressed. Not only the intended gas but also unintended gas may be dissociated to lower the gas detection accuracy.

  Therefore, the present disclosure provides a gas sensor element including an insulating protective layer having a porous portion, which is unlikely to be damaged even when used in a low temperature environment, and a gas sensor including such a gas sensor element Intended to provide.

  One aspect of the present disclosure is a sensor element including a cell, an insulating protective layer, and an electrode contact portion, the cell including a solid electrolyte layer, a first electrode, and a second electrode, and the insulating protective layer A porous portion and a dense portion, the porous portion being in contact with the electrode contact portion, being exposed on the outer surface of the insulating protective layer opposite to the contact surface with the cell, the porous portion being porous The cross-sectional area which looked at the part exposed to the outer surface among the mass parts from the lamination direction is smaller than the cross-sectional area of the 1st electrode when seeing through in the lamination direction.

  The solid electrolyte layer is plate-shaped, the first electrode is disposed on the first surface of the solid electrolyte layer, and the second electrode is disposed on the second surface of the solid electrolyte layer. The insulating protective layer is formed of a plate-like insulator laminated on the first surface of the solid electrolyte layer in the cell. The porous portion is provided at the formation position of the first electrode, and the dense portion has a porosity lower than that of the porous portion and is formed so as to surround the periphery of the porous portion. The electrode contact portion is formed of a porous body that covers at least the entire first electrode of the cell and contacts the first electrode. The “position where the first electrode is formed” means the position where the first electrode is formed when the element is seen through from the stacking direction.

  In this gas sensor element, the cross-sectional area of the porous portion is smaller than the cross-sectional area of the first electrode, whereby the area of the porous portion exposed on the outer surface of the insulating protective layer can be reduced, and the stress due to thermal shock is small. As a result, damage can be suppressed, and damage to the insulating protective layer due to a volume change of water contained in the porous portion can be suppressed.

  By adopting a configuration in which the electrode contact portion covers the entire first electrode and contacts the first electrode, the first electrode can contact the electrode contact portion in a region other than the contact surface with the solid electrolyte layer. Gas can be delivered. That is, by adopting a configuration in which the first electrode transfers gas with the porous portion via the electrode contact portion, the exposed area of the porous portion is smaller than the cross-sectional area of the first electrode. However, reduction in the amount of gas that can be transferred between the porous portion and the first electrode can be suppressed. As a result, in the gas sensor element, the delivery state of the gas between the porous portion and the first electrode is improved, and there is no need to increase the applied voltage, so that the adverse effect on the gas detection function in the cell can be reduced.

Therefore, according to this gas sensor element, damage in a low temperature environment is not likely to occur, and an adverse effect on the gas detection function can be reduced.
In addition, since the porous part is a porous structure, it is comprised so that permeation | transmission of gas is possible.

Next, in the above-described gas sensor element, the porosity of the electrode contact portion may be larger than the porosity of the porous portion.
Thereby, it is possible to further suppress reduction in the amount of gas that can be transferred between the electrode contact portion and the first electrode. Thereby, the delivery state of the gas between the porous portion and the first electrode through the electrode contact portion is further improved.

Next, in the gas sensor element described above, the thickness dimension of the electrode contact portion in the stacking direction may be smaller than the thickness dimension of the porous portion.
Since the electrode contact portion having a large cross-sectional area has a smaller thickness than the porous portion having a small cross-sectional area, the volume occupied by the electrode contact portion and the porous portion in the insulating protective layer can be reduced. Thereby, since the volume change amount of the electrode contact part and the porous part in a low temperature environment can be reduced, the damage of the insulating protective layer can be suppressed.

Next, in the gas sensor element described above, a plurality of porous portions may be provided, and the total area of the cross-sectional areas of the plurality of porous portions may be smaller than the cross-sectional area of the first electrode.
This gas sensor element does not have a structure having a single porous portion, but can take the structure having a plurality of porous portions, thereby dispersing the stress caused by the volume change of the water contained in the porous portion. The damage to the insulating protective layer can be further suppressed.

  Next, in the above gas sensor element, a porous protective cover layer covering at least the exposed portion of the porous portion of the insulating protective layer is further provided, and the solid electrolyte layer has an elongated shape extending in the longitudinal direction. When the end close to the first electrode of the two ends in the longitudinal direction of the solid electrolyte layer is the front end, and the other end is the rear end, the porous portion is the longitudinal portion of the electrode contact portion. It may be arranged to abut the tip area in the direction.

  By providing the porous portion arranged in this manner, the application area of the protective cover layer covering the tip of the gas sensor element can be reduced, and the material cost of the protective cover layer can be reduced. The front end region of the electrode contact portion means the region on the front end side when the electrode contact portion is bisected into the region on the front end side and the region on the rear end side.

  Another aspect of the present disclosure is a gas sensor including a gas sensor element that detects a specific gas included in a measurement target gas, and includes any one of the gas sensor elements described above as the gas sensor element.

  By providing the above-described gas sensor element, this gas sensor is less likely to be damaged in a low temperature environment and can reduce the adverse effect on the gas detection function.

It is a sectional view showing the state where the air-fuel ratio sensor of an embodiment was fractured along the direction of an axis. It is a perspective view showing a gas sensor element. It is a perspective view which disassembles and shows a gas sensor element. It is an end elevation showing the AA view end surface in the gas sensor element of FIG. First explanation for explaining the cross-sectional area and the positional relationship of the porous electrode, the electrode contact portion, and the porous portion when the gas sensor element of FIG. 4 is viewed in the B-B arrow direction (stacking direction) FIG. The second description for explaining the cross-sectional area and the positional relationship of each of the porous electrode, the electrode contact portion, and the porous portion when the gas sensor element of FIG. 4 is seen through in the B-B arrow direction (lamination direction). FIG. It is explanatory drawing regarding the manufacturing method of the molded object of a gas sensor element. It is explanatory drawing which shows the manufacture middle stage of a gas sensor element. It is the measurement result which measured the correlation with the cross-sectional area of a porous part, and the applied voltage to an oxygen pump cell. It is a perspective view which shows a 2nd gas sensor element. It is explanatory drawing which shows each cross-sectional area and positional relationship of the porous electrode in a 2nd gas sensor element, an electrode contact part, and several porous parts.

Hereinafter, embodiments to which the present invention is applied will be described using the drawings.
In the embodiment described below, a full-range air-fuel ratio sensor (hereinafter, also simply referred to as an air-fuel ratio sensor) is taken as an example of an oxygen sensor which is a type of gas sensor. Specifically, for use in air-fuel ratio feedback control in automobiles and various internal combustion engines, a gas sensor element (detection element) for detecting a specific gas (oxygen) in the exhaust gas to be measured is assembled. The air-fuel ratio sensor attached to the exhaust pipe will be described as an example.

[1. First embodiment]
[1-1. overall structure]
The entire configuration of an air-fuel ratio sensor in which the gas sensor element of the present embodiment is used will be described based on FIG. FIG. 1 is a cross-sectional view showing an internal configuration of an air-fuel ratio sensor.

  As shown in FIG. 1, the air-fuel ratio sensor 1 in the present embodiment includes a cylindrical metal shell 5 having a screw 3 for fixing to an exhaust pipe formed on the outer surface, and an axial direction (air-fuel ratio sensor 1 Longitudinal direction: plate-shaped gas sensor element 7 extending in the vertical direction in FIG. 1, cylindrical ceramic sleeve 9 disposed so as to surround the radial direction of gas sensor element 7, and insertion hole 11 penetrating in the axial direction The insulating contact members 13 (separator 13) are disposed such that the inner wall surface of the gas sensor element 7 surrounds the rear end portion of the gas sensor element 7, and five pieces are disposed between the gas sensor element 7 and the separator 13 (FIG. And two connection terminals 15).

  The gas sensor element 7 is provided with a rectangular parallelepiped element main body 70 extending in the longitudinal direction and a porous protective layer 17 covering the distal end side of the element main body 70, as described in detail later. The element main body 70 includes a detection unit 90 on the tip end side for detecting a specific gas contained in the gas to be measured. Further, the gas sensor element 7 has electrode pads 25, 25 on the first main surface 21 and the second main surface 23, which have a positional relationship between the front and back, of the outer surface on the rear end side (upper in FIG. 1: rear end in the longitudinal direction). 27, 29, 31 and 33 (for details, refer to FIG. 2 and FIG. 3) are formed.

  The connection terminals 15 are electrically connected to the electrode pads 25, 27, 29, 31, and 33 of the gas sensor element 7, respectively, and are also electrically connected to lead wires 35 disposed inside the sensor from the outside. And forms a current path of current flowing between an external device to which the lead wire 35 is connected and the electrode pad 25, 27, 29, 31, 33.

  The metal shell 5 has a through hole 37 penetrating in the axial direction, and has a substantially cylindrical shape having a shelf 39 projecting inward in the radial direction of the through hole 37. In the metal shell 5, the detection unit 90 is disposed closer to the tip than the tip of the through hole 37, and the electrode pads 25, 27, 29, 31, 33 are disposed closer to the rear than the rear end of the through hole 37. Thus, the gas sensor element 7 inserted into the through hole 37 is held.

  Further, an annular ceramic holder 41, a talc ring 43, a talc ring 45, and the above-mentioned ceramic sleeve 9 are provided inside the through hole 37 of the metal shell 5 so as to surround the circumference of the gas sensor element 7 in the radial direction. The layers are stacked in order from the front end side to the rear end side.

  A caulking packing 49 is disposed between the ceramic sleeve 9 and the rear end portion 47 of the metal shell 5, while a talc ring 43 or the like is disposed between the ceramic holder 41 and the shelf portion 39 of the metal shell 5. A metal holder 51 for holding the ceramic holder 41 is disposed. The rear end portion 47 of the metal shell 5 is crimped so as to press the ceramic sleeve 9 to the tip end side via the crimp packing 49.

  Furthermore, a protector 55 having a double structure made of metal (for example, stainless steel or the like) covering the projecting portion of the gas sensor element 7 is attached to the outer periphery of the front end portion 53 of the metal shell 5 by welding or the like.

  On the other hand, an outer cylinder 57 is fixed to the outer periphery of the metal shell 5 on the rear end side. Further, in the opening on the rear end side of the outer cylinder 57, five lead wires 35 (three are shown in FIG. 1) electrically connected to the respective electrode pads 25, 27, 29, 31, and 33, respectively. The grommet 61 in which the lead wire insertion hole 59 by which 1 is inserted is formed is arrange | positioned.

A collar portion 63 is formed on the outer periphery of the separator 13, and the collar portion 63 is fixed to the outer cylinder 57 via the holding member 65.
[1-2. Configuration of gas sensor element]
Next, the configuration of the gas sensor element 7, which is a main part of the present embodiment, will be described in detail based on FIGS.

FIG. 2 is a perspective view showing the appearance of the gas sensor element 7.
As shown in FIG. 2, the gas sensor element 7 is a long plate material extending in the longitudinal direction (Y-axis direction). In FIG. 2, the longitudinal direction is along the axis O of the gas sensor. The Z-axis direction in FIG. 2 is a thickness direction perpendicular to the longitudinal direction, and the X-axis direction is a width direction perpendicular to the longitudinal direction and the thickness direction.

  The gas sensor element 7 includes a rectangular parallelepiped element body 70 extending in the longitudinal direction, and a porous protective layer 17 covering the tip side (lower side in FIG. 2) of the element body 70. The element main body portion 70 is configured by laminating a plate-like element portion 71 extending in the longitudinal direction and a plate-like heater 73 similarly extending in the longitudinal direction (see FIG. 3). The element main body 70 includes a detection unit 90 on the tip end side for detecting a specific gas contained in the gas to be measured. The protective layer 17 is made of porous alumina, and covers the entire tip surface 127 of the element main body 70 and the side surfaces (the first main surface 21, the second main surface 23, It is provided on a part of the first side surface 111 and the second side surface 113).

FIG. 3 shows an exploded perspective view of the gas sensor element 7. In FIG. 3, the protective layer 17 is not shown.
The element main body 70 of the gas sensor element 7 is disposed on one side (upper side in FIG. 3) of the stacking direction, as shown in an exploded manner in FIG. And a plate-like heater 73 disposed on the opposite side (back side) of the portion 71 and also extending in the longitudinal direction.

Among them, the element unit 71 includes an oxygen concentration battery cell 81, an oxygen pump cell 89, an insulating spacer 93, an electrode contact portion 92, and an insulating protection layer 96.
The oxygen concentration battery cell 81 includes a solid electrolyte body 75, a porous electrode 77, a lead portion 77a, a porous electrode 79, and a lead portion 79a.

  The solid electrolyte body 75 is a plate-shaped member mainly made of zirconia. The pair of porous electrodes 77 and 79 are disposed on the front and back surfaces of the solid electrolyte body 75 so as to sandwich the solid electrolyte body 75.

  The lead portion 77a has one end connected to the porous electrode 77 and is arranged to extend in the longitudinal direction (left and right direction in FIG. 3) of the gas sensor element 7 (element body portion 70). The lead portion 79a has one end connected to the porous electrode 79 and is arranged to extend in the longitudinal direction (left and right direction in FIG. 3) of the gas sensor element 7 (element body portion 70).

The oxygen pump cell 89 includes a solid electrolyte body 83, a porous electrode 85, a lead portion 85a, a porous electrode 87, and a lead portion 87a.
The solid electrolyte body 83 is a plate-shaped member mainly made of zirconia, and includes a surface 83a and a back surface 83b. The pair of porous electrodes 85 and 87 are respectively disposed on the surface 83 a and the back surface 83 b of the solid electrolyte body 83 so as to sandwich the solid electrolyte body 83.

  The lead portion 85a has one end connected to the porous electrode 85 and is arranged to extend in the longitudinal direction (left and right direction in FIG. 3) of the gas sensor element 7 (element body portion 70). The lead portion 87a has one end connected to the porous electrode 87, and is arranged to extend in the longitudinal direction (left and right direction in FIG. 3) of the gas sensor element 7 (element body portion 70).

The solid electrolyte bodies 75 and 83 are formed of zirconia in which yttria is dissolved as a stabilizer.
The porous electrodes 77, 79, 85, 87 and the lead portions 77a, 79a, 85a, 87a are mainly formed of Pt.

  The insulating spacer 93 is a plate-shaped member mainly made of alumina, and includes a hollow gas measurement chamber 91. The insulating spacer 93 is stacked between the oxygen concentration battery cell 81 and the oxygen pump cell 89. Thus, the insulating spacer 93 forms at least a part of the wall surface of the gas measurement chamber 91. Inside the gas measurement chamber 91, one porous electrode 77 of the oxygen concentration battery cell 81 and one porous electrode 87 of the oxygen pump cell 89 are disposed so as to be exposed.

  On the side surface of the element unit 71 (the side surface of the insulating spacer 93), two gas introduction parts 94 serving as intake ports for exhaust gas (measurement target gas) are formed. The gas introduction part 94 communicates with the gas measurement chamber 91. doing. A diffusion control portion 95 is formed on each path from the two gas introduction portions 94 to the gas measurement chamber 91. The diffusion control portion 95 is made of, for example, a porous body made of alumina or the like, and performs rate control when the gas to be measured flows into the gas measurement chamber 91. The diffusion control part 95 is provided in a state where a part thereof is exposed to the outside from the gas introduction part 94.

  That is, in the gas sensor element 7, the gas introduction part 94 is formed in two different directions on the outermost surface of the element body 70, and the diffusion control part 95 is exposed in two different directions. .

  The insulating and protective layer 96 includes an insulating substrate 97 and a porous portion 99. The insulating and protective layer 96 is stacked on the surface of the oxygen pump cell 89 on which the porous electrode 85 is formed (specifically, the surface 83 a of the solid electrolyte body 83).

  The insulating substrate 97 is a plate-shaped member mainly made of alumina, and includes a space portion 97 a penetrating in the thickness direction. The space 97 a is formed at a position corresponding to the porous electrode 85 in the insulating substrate 97. The space 97a includes a first space 97a1 and a second space 97a2. The first space portion 97a1 is formed so that the cross-sectional area as viewed in the thickness direction is smaller than the cross-sectional area of the porous electrode 85 and opens at the first major surface 21 of the insulating substrate 97 There is. The second space 97a2 is formed such that the cross-sectional area as viewed in the thickness direction is larger than the cross-sectional area of the porous electrode 85, and the second space 97a2 opens at the surface of the insulating substrate 97 facing the oxygen pump cell 89. It is done.

  The porous portion 99 is made of a porous body mainly composed of alumina. The porous portion 99 is configured to be permeable to gas because it has a porous structure. The porous portion 99 is disposed in the first space portion 97a1. The porous portion 99 is exposed to the outer surface (the first main surface 21 of the insulating substrate 97) of the insulating protection layer 96 on the opposite side to the contact surface with the oxygen pump cell 89.

  The insulating substrate 97 has a porosity lower than that of the porous portion 99 and has a shape surrounding the periphery of the porous portion 99. In the present embodiment, the insulating substrate 97 is formed in a non-porous state. The porosity of the insulating substrate 97 is 0 [vol%], and the porosity of the porous portion 99 is 36 [vol%]. The method of calculating the porosity is calculated by “porosity [vol%] = (carbon volume) / (carbon volume + ceramic volume)” in the porogen (carbon) and the ceramic body as the material. The electrode contact portion 92 is disposed between the oxygen pump cell 89 and the insulating protection layer 96. In detail, the electrode contact portion 92 is disposed in the second space portion 97a2.

  The electrode contact portion 92 is made of a porous body mainly made of alumina. The porosity of the electrode contact portion 92 is larger than the porosity of the porous portion 99. The porosity of the electrode contact portion 92 is 58 [vol%]. The electrode contact portion 92 and the porous portion 99 are provided in a gas movement path connecting the porous electrode 85 of the oxygen pump cell 89 and the outside of the gas sensor element 7.

  The gas measurement chamber 91 is formed to be located on the tip end side (left side in FIG. 3) of the element main body portion 70 (specifically, the element portion 71). The formation region of the gas measurement chamber 91 and the region on the tip end side of the gas measurement chamber 91 in the longitudinal direction of the element unit 71 are provided as a detection unit 90 for detecting oxygen.

On the other hand, the heater 73 is formed by sandwiching the heating resistor pattern 105 mainly made of Pt between the insulating substrates 101 and 103 mainly made of alumina.
In such a gas sensor element 7, three electrode pads 25, 27, 29 are formed on the rear end side (right side in FIG. 3) of the first main surface 21, and two are provided on the rear end side of the second main surface 23. Electrode pads 31 and 33 are formed.

  Among these, one electrode pad 29 (right electrode pad in FIG. 2) of the first main surface 21 is a through hole 161 provided in the insulating substrate 97 and a through hole provided in the solid electrolyte body 83 as shown in FIG. The electrode 165 is electrically connected to the porous electrode 77 of the oxygen concentration battery cell 81 through the through hole 171 provided in the insulating spacer 93 and the lead 77a. The electrode pad 29 is also electrically connected to the porous electrode 87 of the oxygen pump cell 89 through the through hole 161 provided in the insulating substrate 97, the through hole 165 provided in the solid electrolyte body 83, and the lead portion 87a. Be done. Therefore, the porous electrode 77 and the porous electrode 87 are electrically connected at the same potential.

  Further, as shown in FIG. 3, the other electrode pads 27 (the center electrode pads in FIG. 2) are provided in the through holes 162 provided in the insulating substrate 97, the through holes 166 provided in the solid electrolyte body 83, and the insulating spacers 93. It is electrically connected to the porous electrode 79 of the oxygen concentration battery cell 81 through the through hole 172 which is formed, the through hole 176 which is provided in the solid electrolyte body 75, and the lead portion 79a. Furthermore, as shown in FIG. 3, the other electrode pad 25 (left electrode pad in FIG. 2) is electrically connected to the porous electrode 85 of the oxygen pump cell 89 through the through hole 163 provided in the insulating substrate 97 and the lead portion 85a. Connected.

  Further, as shown in FIG. 3, the electrode pads 31 and 33 are electrically connected to both ends of the heating resistor pattern 105 through the through holes 181 and 182 provided in the insulating substrate 103.

  Returning to FIG. 2, since the gas sensor element 7 having the above-described configuration is a plate member having a long, substantially rectangular parallelepiped shape, the corner portion on the outer peripheral side in the radial direction is along the longitudinal direction (Y direction in FIG. 2) And four sides (longitudinal ridgelines) H1, H2, H3, and H4.

  Specifically, the gas sensor element 7 is connected to the first major surface 21 and the second major surface 23 and the first major surface 21 and the second major surface 23 as four outer peripheral walls extending along the longitudinal direction of the gas sensor element 7 The first side 111 and the second side 113. In addition, a first side H1 which is a ridge line between the first major surface 21 and the first side surface 111, a second side H2 which is a ridge line between the first major surface 21 and the second side surface 113, and A third side H3 which is a ridge between the main surface 23 and the second side surface 113 and a fourth side H4 which is a ridge between the second main surface 23 and the first side 111 are provided.

A rear end face 129 perpendicular to the longitudinal direction is formed on the rear end side (upper side in FIG. 2) of the gas sensor element 7.
The protective layer 17 is made of porous alumina, and is formed so as to cover at least the detection portion 90 in the element body portion 70. In detail, the protective layer 17 is formed to cover at least the exposed portion of the porous portion 99 of the insulating protective layer 96. Further, the protective layer 17 is formed so as to cover at least the exposed portion of the diffusion control portion 95 in the side surface of the element portion 71 (the side surface of the insulating spacer 93).

[1-3. Internal structure on the tip side of the gas sensor element]
Next, the internal structure on the tip side of the gas sensor element 7 will be described.
FIG. 4 is an end view showing an end surface of the gas sensor element 7 of FIG. 2 as viewed from A-A, and an end view showing an internal structure on the tip side of the gas sensor element 7. In FIG. 4, illustration of the protective layer 17 is omitted.

  As shown in FIG. 4, the gas sensor element 7 includes two cells (oxygen concentration battery cell 81 and oxygen pump cell 89), and these two cells are stacked via the insulating spacer 93.

  The oxygen concentration battery cell 81 is configured by arranging a pair of porous electrodes 77 and porous electrodes 79 on the front surface and the back surface of the solid electrolyte body 75, respectively. The oxygen pump cell 89 is configured by arranging a pair of porous electrodes 85 and porous electrodes 87 on the front and back surfaces of the solid electrolyte body 83, respectively.

The gas measuring chamber 91 is a space in which the upper surface is formed by the oxygen concentration battery cell 81, the lower surface is formed by the oxygen pump cell 89, and the side wall is formed by the insulating spacer 93.
Inside the gas measurement chamber 91, the porous electrode 77 of the oxygen concentration battery cell 81 and the porous electrode 87 of the oxygen pump cell 89 are disposed so as to be exposed.

  Here, in FIG. 5 and FIG. 6, each of the porous electrode 85, the electrode contact portion 92, and the porous portion 99 when the gas sensor element 7 of FIG. 4 is seen through in the B-B arrow direction (lamination direction). The explanatory view for explaining section area and physical relationship is shown. In each of FIGS. 4, 5 and 6, the left and right direction of the figure is the longitudinal direction of the gas sensor element 7, the left side of the figure is the tip end side, and the right side of the figure is the rear end side.

  As shown in FIGS. 4, 5 and 6, the electrode contact portion 92 is formed so as to cover at least the whole of the porous electrode 85 of the oxygen pump cell 89 and to be in contact with the porous electrode 85.

  The porous portion 99 is in contact with the electrode contact portion 92. In detail, the porous portion 99 is in contact with the tip end region of the electrode contact portion 92. The distal end region of the electrode contact portion 92 is a region that is on the distal end side when the electrode contact portion 92 is bisected in the longitudinal direction of the solid electrolyte body 83.

  The area of the porous portion 99 exposed to the first major surface 21 (in other words, the cross-sectional area when the porous portion 99 is viewed from the stacking direction) is the cross section of the porous electrode 85 when seen through in the stacking direction. Smaller than the area.

  The thickness dimension D1 of the electrode contact portion 92 in the stacking direction is smaller than the thickness dimension D2 of the porous portion 99. In the present embodiment, the thickness dimension D1 of the electrode contact portion 92 is 400 μm, and the thickness dimension D2 of the porous portion 99 is 15 μm.

[1-4. Manufacturing method of gas sensor]
A method of manufacturing the air-fuel ratio sensor 1 of the present embodiment will be described based on FIGS. 7 to 8.
FIG. 7 is an explanatory view of a method of manufacturing the molded body 141 of the gas sensor element, and FIG. 8 is an explanatory view showing a manufacturing step of the gas sensor element.

  In the case of manufacturing the gas sensor element 7, first, various laminated materials serving as materials of the well-known gas sensor element 7, that is, unbaked solid electrolyte sheets serving as the solid electrolyte bodies 75 and 83 of the element portion 71, and insulation protection of the element portion 71 A non-sintered insulation sheet to be the layer 96, a non-sintered insulation sheet to be the porous portion 99, and a non-sintered insulation sheet to be the insulating substrates 101 and 103 of the heater 73 are laminated to obtain a non-crimped laminate. In addition, the non-baked electrode pad used as electrode pad 25,27,29,31,33 etc. are formed in this non-crimped laminated body.

  Among them, for example, when forming a non-fired solid electrolyte sheet, first, alumina powder, butyral resin, etc. are added to ceramic powder mainly composed of zirconia, and mixed solvents (toluene and methyl ethyl ketone) are further mixed. To form a slurry. Then, the slurry is formed into a sheet by a doctor blade method, and the mixed solvent is volatilized to produce an unbaked solid electrolyte sheet.

  Moreover, when forming a non-baked insulating sheet, first, butyral resin and dibutyl phthalate (hereinafter, also described as DBP) are added to ceramic powder mainly composed of alumina, and a mixed solvent (toluene and methyl ethyl ketone) is further added. Mix to form a slurry. Then, the slurry is formed into a sheet by a doctor blade method, and the mixed solvent is evaporated to produce a non-baked insulating sheet.

  Furthermore, when forming a non-fired diffusion-controlled portion, first, a paste is formed by dispersing alumina powder, porogen (such as carbon powder), and binder by wet mixing. The binder comprises butyral resin. Using this paste, an unfired diffusion-controlled portion is formed in a portion that becomes the diffusion-controlled portion 95 after firing.

  Further, in the case of forming the unfired electrode contact portion, first, a paste in which alumina powder, porogen (such as carbon powder) and a binder are dispersed by wet mixing is generated. The binder uses butyral resin. Using this paste, a non-fired porous body is formed in a portion to be the electrode contact portion 92 after firing.

  When an unfired porous portion is to be formed, first, a slurry is formed by dispersing alumina powder, porogen (such as carbon powder), and plasticizer by wet mixing. The plasticizer comprises butyral resin and DBP. The slurry is formed into a sheet by a doctor blade method, and the mixed solvent is evaporated to prepare a sheet for an unfired porous part. The unfired porous part sheet is embedded in the unfired insulating sheet in the portion to be the porous part 99 after firing to form the unfired porous part.

  At this time, by adjusting the binder amount in the paste, the composition ratio of the solid content, the addition amount of the pore forming agent, and the like, the diffusion resistance in the diffusion controlled portion 95, the porous portion 99, and the electrode contact portion 92 after baking. And porosity can be adjusted arbitrarily.

  In addition, in the case of forming the unfired porous electrode and the lead portion, a paste in which platinum, partially stabilized zirconia, and a binder are dispersed by wet mixing is generated. Using this paste, unfired porous electrodes and lead portions are formed on the portions that become the porous electrodes and lead portions after firing. At this time, by adjusting the binder amount, the composition ratio of the solid content, the addition amount of the pore forming agent, and the like, it is possible to arbitrarily adjust the respective diffusion resistances in the porous electrode and the lead portion after firing.

  Then, the non-crimped laminated body is pressurized at 1 MPa to obtain a crimped molded body 141 as shown in FIG. In addition, about the manufacturing method until it obtains the non-pressure-bonded laminated body before pressurization, since it is the same as the manufacturing method of a well-known gas sensor element, detailed description is abbreviate | omitted.

  Then, the molded body 141 obtained by pressing is cut into a predetermined size, whereby a plurality of (for example, 10) unsintered laminates whose sizes substantially match those of the element portion 71 and the heater 73 of the gas sensor element 7 Get the body.

  Thereafter, the unbaked laminate is de-resinized (degreasing step), and main firing is further performed at a firing temperature of 1500 ° C. for 1 hour (baking step) to obtain a fired laminate 143 as shown in FIG. The fired laminate 143 corresponds to the element body 70.

After the element body 70 is obtained in this manner, a non-sintered protective layer to be the protective layer 17 (see FIG. 2) is formed around the tip of the element body 70 after firing.
Thereafter, heat treatment of the unfired protective layer is performed. Specifically, the element body 70 on which the unbaked protective layer is formed is heat-treated at a heat treatment temperature of 1000 ° C. for a heat treatment time of 3 hours to obtain the gas sensor element 7 on which the protective layer 17 is formed.

After the gas sensor element 7 is obtained in this manner, an assembly step of assembling the gas sensor element 7 to the metal shell 5 is performed.
That is, in this step, the gas sensor element 7 manufactured by the above-mentioned manufacturing method is inserted into the metal holder 51, and further, the gas sensor element 7 is fixed by the ceramic holder 41 and the talc ring 43 to manufacture an assembly. Thereafter, the assembled body is fixed to the metal shell 5, and the rear end side of the gas sensor element 7 in the direction of the axis O is inserted into the talc ring 45 and the ceramic sleeve 9 and inserted into the metal shell 5.

Then, the ceramic sleeve 9 is crimped by the rear end portion 47 of the metal shell 5 to produce a lower assembly. A protector 55 is attached to the lower assembly in advance.
On the other hand, the outer cylinder 57, the separator 13, the grommet 61 and the like are assembled to fabricate an upper assembly. Then, the lower assembly and the upper assembly are joined to obtain the air-fuel ratio sensor 1.

[1-5. Measurement result]
Here, with respect to the applied voltage V1 to the oxygen pump cell 89 for pumping oxygen in the gas sensor element 7, the measurement result of measuring the correlation between the cross-sectional area S1 of the porous portion 99 and the applied voltage V1 will be described.

  In the measurement, assuming that the same size as the cross-sectional area of the electrode contact portion 92 is 100%, the application of oxygen necessary for pumping when the cross-sectional area S1 is changed in five steps (see FIG. 9) The rate of increase of the voltage V1 was measured. Specifically, the increase rate (voltage increase rate ΔV1 [%]) of the applied voltage V1 was measured with the applied voltage V1 when the cross-sectional area S1 of the porous portion 99 was 100% as 100% (reference).

  As shown in FIG. 9, when the cross-sectional area S1 is 3.3%, the voltage increase rate ΔV1 is 78.6%, and the voltage V1 applied to the oxygen pump cell 89 significantly increases. When the cross-sectional area S1 is 4.2% or more, the voltage increase rate ΔV1 is 5.2% or less, and it can be seen that a large increase in the applied voltage V1 can be suppressed.

  Therefore, the porous portion 99 is formed to secure the cross-sectional area of 4.2% or more when the cross-sectional area of the electrode contact portion 92 is taken as a reference (100%). A significant increase in the applied voltage V1 can be suppressed.

[1-6. effect]
As described above, the gas sensor element 7 in the air-fuel ratio sensor 1 of the present embodiment has a configuration in which the cross-sectional area of the porous portion 99 is smaller than the cross-sectional area of the porous electrode 85.

  For this reason, the gas sensor element 7 can reduce the area of the porous portion 99 exposed to the outer surface of the insulating protection layer 96, and can reduce the stress due to thermal shock to suppress the breakage of the insulating protection layer 96. It is possible to suppress damage to the insulating protective layer 96 due to a volume change of water contained in the element 99.

Further, the gas sensor element 7 has a configuration in which the electrode contact portion 92 covers the whole of the porous electrode 85 and contacts the porous electrode 85.
For this reason, the porous electrode 85 can transfer gas with the electrode contact portion 92 in a region other than the contact surface with the solid electrolyte body 83. That is, by adopting a configuration in which the porous electrode 85 transfers gas with the porous portion 99 via the electrode contact portion 92, the exposed area of the porous portion 99 is greater than the cross-sectional area of the porous electrode 85. Even if the configuration is too small, reduction in the amount of gas that can be transferred between the porous portion 99 and the porous electrode 85 can be suppressed.

  Thereby, in the gas sensor element 7, the gas delivery state between the porous portion 99 and the porous electrode 85 becomes good, and there is no need to increase the voltage applied to the oxygen pump cell 89. The adverse effect on the detection function can be reduced.

Therefore, according to the gas sensor element 7, damage in a low temperature environment is not likely to occur, and an adverse effect on the gas detection function can be reduced.
Next, in the gas sensor element 7, the porosity of the electrode contact portion 92 is larger than the porosity of the porous portion 99.

  As a result, it is possible to further suppress reduction in the amount of gas that can be transferred between the electrode contact portion 92 and the porous electrode 85. Thereby, the delivery state of the gas between the porous portion 99 and the porous electrode 85 via the electrode contact portion 92 is further improved.

Next, in the gas sensor element 7, the thickness dimension D1 of the electrode contact portion 92 in the stacking direction is smaller than the thickness dimension D2 of the porous portion 99.
Since the electrode contact part 92 having a large cross-sectional area has a smaller thickness than the porous part 99 having a small cross-sectional area (D1 <D2), the electrode contact part 92 and the porous part 99 in the insulating protective layer 96 The occupied volume can be reduced. Thereby, since the volume change amount of the electrode contact part 92 and the porous part 99 in a low temperature environment can be reduced, the damage of the insulating protective layer 96 can be suppressed.

Next, in the gas sensor element 7, the porous portion 99 is disposed to abut on the tip end region in the longitudinal direction of the electrode contact portion 92.
By providing the porous portion 99 disposed in this manner, the application region of the protective layer 17 covering the tip of the gas sensor element 7 can be reduced, and the material cost of the protective layer 17 can be reduced. The front end region of the electrode contact portion 92 means a region on the front end side when the electrode contact portion is bisected into a region on the front end side and a region on the rear end side.

[1-7. Correspondence with the claims]
Here, the correspondence of the wording in a claim and this embodiment is explained.
The air-fuel ratio sensor 1 corresponds to an example of a gas sensor, and the gas sensor element 7 corresponds to an example of a sensor element.

  The oxygen pump cell 89 corresponds to an example of a cell, the solid electrolyte body 83 corresponds to an example of a solid electrolyte layer, the surface 83 a corresponds to an example of a first surface, and the back surface 83 b corresponds to an example of a second surface The quality electrode 85 corresponds to an example of the first electrode, and the porous electrode 87 corresponds to an example of the second electrode.

  The insulating and protective layer 96 corresponds to an example of the insulating and protective layer, the porous portion 99 corresponds to an example of a porous portion, and the insulating substrate 97 corresponds to an example of a dense portion. The electrode contact portion 92 corresponds to an example of the electrode contact portion, and the protective layer 17 corresponds to an example of a protective cover layer.

[2. Second embodiment]
As a second embodiment, the second gas sensor element 107 configured to include a plurality of porous portions will be described.

The second gas sensor element 107 is a sensor element configured by replacing the porous portion 99 with a plurality of porous portions 199 in the gas sensor element 7 of the first embodiment.
The second gas sensor element 107 has the same outer dimensions as the gas sensor element 7 and can be used as a sensor element in the air-fuel ratio sensor by being provided instead of the gas sensor element 7 in the air-fuel ratio sensor 1 of the first embodiment. .

As shown in FIGS. 10 and 11, the second gas sensor element 107 includes a plurality of porous portions 199.
Each of the plurality of porous portions 199 has a circular cross-sectional shape. The total value of the cross-sectional areas of the plurality of porous portions 199 is smaller than the cross-sectional area of the porous electrode 85. One porous portion 199 is not arranged so that the whole portion overlaps the electrode contact portion 92, and a partial region overlaps the electrode contact portion 92, and the other region does not overlap the electrode contact portion 92. It is arranged.

Thus, in the second gas sensor element 107, a plurality of porous portions 199 are provided, and the total area of the cross-sectional areas of the plurality of porous portions 199 is smaller than the cross-sectional area of the porous electrode 85.
That is, the second gas sensor element 107 does not have a structure having a single porous portion, but has a structure having a plurality of porous portions 199. By adopting such a structure, the second gas sensor element 107 can disperse the stress generated along with the volume change of the water contained in the porous portion 199, and can further suppress the breakage of the insulating protection layer 96.

  In addition, the second gas sensor element 107 is disposed such that a part of one porous portion 199 overlaps the electrode contact portion 92. Such a second gas sensor element 107 has a plurality of porous portions while securing a large distance between the plurality of porous portions 199 as compared with a configuration in which the whole of one porous portion 199 overlaps the electrode contact portion 92. The part 199 can be arranged. Thus, breakage of the insulating substrate 97 can be suppressed due to the distance between the plurality of porous portions 199 being short. In this case, as a failure of the insulating substrate 97, for example, a crack may be generated to connect a plurality of porous portions 199 of the insulating substrate 97.

  Here, the correspondence of the wording in a claim and this 2nd embodiment is explained. In the second embodiment, the second gas sensor element 107 corresponds to an example of a sensor element, and the plurality of porous portions 199 correspond to an example of a plurality of porous portions.

[3. Other embodiments]
As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, It is possible in the range which does not deviate from the summary of this invention to implement in various aspects.

For example, the porous portion is not limited to a square or a circle in cross-sectional shape, and may be a polygon (a pentagon, a hexagon, or the like) or an oval.
Next, the thickness dimension of the electrode contact portion may be smaller than the thickness dimension of the porous portion, and may be at least 15 μm or more. Thus, by defining the thickness dimension of the electrode contact portion and securing the volume of the electrode contact portion to a predetermined value or more, a gas that can be transferred between the electrode contact portion and the porous electrode per unit time It is possible to suppress the limitation of the amount of This enables oxygen pumping without significantly increasing the voltage applied to the oxygen pump cell.

  Next, the function of one component in the above embodiment may be shared by a plurality of components or the function of a plurality of components may be performed by one component. Further, part of the configuration of the above embodiment may be omitted. In addition, at least a part of the configuration of the above-described embodiment may be added to or replaced with the configuration of the other above-described embodiment. In addition, all the aspects contained in the technical thought specified from the wording as described in a claim are an embodiment of this indication.

  DESCRIPTION OF SYMBOLS 1 ... Air-fuel ratio sensor, 7 ... Gas sensor element, 17 ... Protective layer, 70 ... Element body part, 71 ... Element part, 73 ... Heater, 75 ... Solid electrolyte body, 77 ... Porous electrode, 79 ... Porous electrode, 81 ... Oxygen concentration battery cell 83: Solid electrolyte body 83a: surface 83b: back surface 85: porous electrode 87: porous electrode 89: oxygen pump cell 92: electrode contact portion 96: insulating protection layer 97: Insulating substrate, 97a: space portion, 97a1: first space portion, 97a2: second space portion, 98: oxygen pump cell, 99: porous portion, 107: second gas sensor element, 199: porous portion.

Claims (6)

A cell having a plate-like solid electrolyte layer, a first electrode disposed on the first surface of the solid electrolyte layer, and a second electrode disposed on the second surface of the solid electrolyte layer;
An insulating protection layer formed of a plate-like insulator laminated on the first surface of the solid electrolyte layer in the cell, the porous portion provided at the formation position of the first electrode, and the porous portion An insulating protective layer comprising a dense portion having a porosity lower than that of the porous portion and surrounding the periphery of the porous portion;
A sensor element comprising
An electrode contact portion formed of a porous body that covers at least the entire first electrode of the cells and contacts the first electrode,
The porous portion is in contact with the electrode contact portion, and is exposed on the outer surface of the insulating protective layer opposite to the contact surface with the cell,
The cross-sectional area of the portion of the porous portion exposed to the outer surface as viewed in the stacking direction is smaller than the cross-sectional area of the first electrode when viewed in the stacking direction.
Gas sensor element. The porosity of the electrode contact portion is larger than the porosity of the porous portion.
The gas sensor element according to claim 1. The thickness dimension of the electrode contact portion in the stacking direction is smaller than the thickness dimension of the porous portion.
The gas sensor element according to claim 1 or 2. The plurality of porous portions are provided, and the total area of the cross-sectional areas of the plurality of porous portions is smaller than the cross-sectional area of the first electrode,
The gas sensor element according to any one of claims 1 to 3. The gas sensor element further includes a porous protective cover layer covering at least the exposed portion of the porous portion of the insulating protective layer,
The solid electrolyte layer has an elongated shape extending in the longitudinal direction, and of the two ends in the longitudinal direction of the solid electrolyte layer, an end near the first electrode is a tip, and the other end is a rear If you
The porous portion is disposed to abut on a tip region in the longitudinal direction of the electrode contact portion.
The gas sensor element according to any one of claims 1 to 4. A gas sensor comprising a gas sensor element for detecting a specific gas contained in a gas to be measured, comprising:
The gas sensor element according to any one of claims 1 to 5 is provided as the gas sensor element,
Gas sensor.

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