JP2018021819A - Gas sensor element and gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor element that achieves prevention against degradation in accuracy of detection of a specified gas and reduction in the size and the power consumption of the gas sensor element, and a gas sensor having the gas sensor element.SOLUTION: A gas sensor element 7 of a NOx sensor 1 has an inner-side electrode 93 and a surrounding electrode 95 as a pair of electrodes of a second pump cell 83. The inner-side electrode 93 and the surrounding electrode 95 are formed in the same plane of a third solid electrolyte body 83a. The surrounding electrode 95 is located on a setting area excluding a one-side projection area TR in a width direction perpendicular to a longitudinal direction of the inner-side electrode 93. In other words, the surrounding electrode 95 is not located on the one-side projection area TR in the width direction. Accordingly, a dimension of the width direction of the gas sensor element 7 is reduced. The reduction of the dimension achieves reduction in the size and the power consumption of the gas sensor element 7.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a gas sensor element for detecting a specific gas contained in a gas to be measured and a gas sensor including the gas sensor element.

Conventionally, a gas sensor element for detecting a specific gas (for example, NOx or the like) contained in a measurement target gas (for example, exhaust gas) and a gas sensor including the gas sensor element are known.
As a gas sensor element, an element including a cell having a plate-type solid electrolyte body and a pair of electrode portions formed on the outer surface of the solid electrolyte body is known.

For example, some gas sensor elements that detect NOx include a first pump cell, a second pump cell, and the like as cells (see, for example, Patent Document 1).
The first pump cell adjusts the oxygen concentration of the measurement target gas by pumping and pumping (pumping) oxygen in the measurement target gas (exhaust gas or the like). The second pump current flows through the second pump cell in accordance with the NOx concentration contained in the measurement target gas whose oxygen concentration is adjusted. The NOx concentration in the measurement target gas can be determined based on the second pump current.

  The cell configuration of the gas sensor element includes a configuration in which one electrode portion and the other electrode portion are disposed on different surfaces of the solid electrolyte body so that the pair of electrode portions sandwich the solid electrolyte body. The electrode part of each is arrange | positioned in the position which differs in the same surface of a solid electrolyte body, respectively etc. (for example, refer patent document 2).

JP 2010-122187 A Special table 2003-508750 gazette

  However, in a cell having a configuration in which a pair of electrode portions are arranged at different positions on the same surface of the solid electrolyte body, a pair of electrode portions is compared with a cell having a configuration in which the pair of electrode portions are arranged to sandwich the solid electrolyte body. There is a concern that the current flowing between the electrode portions may be reduced.

  In other words, in a cell having a configuration in which a pair of electrode portions are arranged so as to sandwich the solid electrolyte body, the area of the electrode portions opposed to each other with the solid electrolyte body interposed therebetween is a region involved in the movement of ions in the solid electrolyte body. .

  Therefore, by enlarging the area where the pair of electrode portions overlap with each other through the solid electrolyte body, it is possible to secure a large area related to the movement of ions in the solid electrolyte body, so that the current flowing between the pair of electrode portions is increased. Is possible.

  On the other hand, in a cell having a configuration in which a pair of electrode portions are arranged on the same surface of the solid electrolyte body, a region in the vicinity of the pair of electrode portions of the solid electrolyte body is mainly a region involved in the movement of ions. However, the electrode portions cannot be overlapped. Therefore, even if the distance between the pair of electrode portions is reduced, it is difficult to ensure a large region related to the movement of ions in the solid electrolyte body.

  In such a configuration, the current flowing between the pair of electrode portions may be small. In particular, in a gas sensor element for detecting NOx, for example, the second pump current flowing through the second pump cell is very small according to the NOx concentration. For this reason, when a 2nd pump cell becomes a structure by which a pair of electrode part is arrange | positioned on the same surface of a solid electrolyte body, there exists a possibility that the detection accuracy of a 2nd pump current may fall and a NOx detection accuracy may fall. is there.

  As a countermeasure, for example, as shown in FIG. 15, a central electrode P2 and a peripheral electrode P3 are provided as a pair of electrode portions on the same surface of the solid electrolyte body P1, and almost the entire circumference (lead portion) of the central electrode P2 is provided. It is conceivable to provide the peripheral electrode P3 in a substantially square frame shape so as to surround the portion excluding P4).

  According to the study by the present inventors, the internal resistance in the second pump cell can be reduced by adopting such a configuration, so that the detection accuracy is hardly lowered even with a small second pump current. It has been found that a decrease in detection accuracy of a specific gas can be suppressed.

However, in this case, the range in which the peripheral electrode P3 is provided is widened, and in particular, the dimension in the width direction of the element (vertical direction in FIG. 15) is increased, which is disadvantageous for downsizing and power saving of the element.
Accordingly, an object of the present invention is to provide a gas sensor element that can suppress a decrease in detection accuracy of a specific gas and that can reduce the size and power consumption of the gas sensor element, and a gas sensor including the gas sensor element. And

  (1) The gas sensor element according to the first aspect of the present invention includes a first measurement chamber, a second measurement chamber, a first pump cell, and a second pump cell, and is exposed to the measurement target gas. It is comprised so that it may extend along a longitudinal direction so that it may reach from a rear end side.

A measurement target gas is introduced into the first measurement chamber. In the second measurement chamber, a measurement target gas into which oxygen has been pumped or pumped in the first measurement chamber is introduced.
The first pump cell has a solid electrolyte body and a pair of first electrodes formed on the solid electrolyte body. One electrode of the pair of first electrodes is exposed to the first measurement chamber. The first pump cell pumps or pumps oxygen to the measurement target gas introduced into the first measurement chamber.

  The second pump cell has a solid electrolyte body and a pair of second electrodes formed on the solid electrolyte body. One electrode of the pair of second electrodes is exposed to the second measurement chamber, and the other electrode of the pair of second electrodes is provided outside the second measurement chamber. The second pump cell is configured such that a second pump current corresponding to the specific gas concentration in the measurement target gas introduced into the second measurement chamber flows.

Furthermore, the inner electrode which is one electrode in the pair of second electrodes and the surrounding electrode which is the other electrode are both formed on the same surface of the solid electrolyte body forming the second pump cell.
In particular, in this gas sensor element, in a plan view when the same surface is viewed from the vertical direction, the peripheral electrode is disposed on a part of the outer peripheral side of the inner electrode and is also positioned on one side in the width direction perpendicular to the longitudinal direction. It is arranged in a setting area excluding the projection area where the electrodes are projected.

  In addition, the outer peripheral portion of the inner electrode includes a facing portion that faces the surrounding electrode, and of the facing portions, the median value of the maximum value and the minimum value of the temperature gradient in the longitudinal direction in the inner electrode when the gas sensor element is used. The length of the high temperature part existing in the above high temperature region is 50% or more of the length of the facing part.

  As described above, in the first aspect, the surrounding electrode is arranged in the setting area excluding the projection area in which the inner electrode is projected on one side in the width direction perpendicular to the longitudinal direction, that is, one side in the width direction. Since no surrounding electrode is arranged in the projection area, the dimension in the width direction of the gas sensor element can be reduced. Thereby, size reduction and power saving of a gas sensor element can be achieved.

  Further, in the first aspect, the center of the maximum value and the minimum value of the temperature gradient in the longitudinal direction in the inner electrode (that is, the temperature gradient when the gas sensor element is used) among the opposing portions of the inner electrode facing the surrounding electrode. The length of the high temperature portion existing in the high temperature region equal to or greater than the value is 50% or more of the length of the facing portion. Of the opposing portions of the inner electrode, the length of the high temperature portion is equal to or greater than the length of the lower temperature portion (ie, the low temperature portion).

  Therefore, even when the surrounding electrode is not provided in one projection region and the dimension in the width direction of the gas sensor element is reduced, the length of the high temperature portion having high electrochemical activity is longer than the length of the low temperature portion. Therefore, the internal resistance (that is, the internal resistance between the inner electrode and the surrounding electrode) can be sufficiently reduced.

For this reason, for example, even when the current flowing between the pair of second electrodes is small like a NOx sensor, it is possible to suppress a decrease in the detection accuracy of the specific gas.
That is, in this 1st aspect, when detecting the specific gas contained in measurement object gas, while being able to suppress the fall of the detection accuracy of specific gas, the size reduction and power saving of a gas sensor element can be achieved. Has an effect.

Here, the facing portion will be described.
For example, as shown in FIG. 6, when an outer peripheral portion is projected from the inner electrode in the longitudinal direction (with the maximum dimension in the width direction), if there is a surrounding electrode at the projection destination, the outer periphery of the projection source It is assumed that the portion is a portion facing the inner electrode. Similarly, when a peripheral electrode is present at the projection destination when the outer peripheral portion is projected from the inner electrode to the other in the width direction (with the maximum dimension in the longitudinal direction), the outer peripheral portion of the projection source is the inner side. It is set as the opposing part of an electrode. In other words, if either one of the conditions is satisfied, it is determined as the facing portion. In addition, about this opposing part, it is the same also in the following 2nd situation.

  The “when using the gas sensor element” means that the temperature of the solid oxide body is not less than the activation temperature (that is, not less than the temperature at which each cell operates) and the gas sensor element is exposed to the measurement target gas. Can be detected (the same applies hereinafter).

The setting area where the surrounding electrodes are arranged is a range excluding the projection area in a range surrounding the periphery (the entire circumference) of the inner electrode in plan view (the same applies hereinafter).
(2) A gas sensor element according to a second aspect of the present invention includes a pair of chambers formed on a measurement chamber into which a measurement target gas is introduced, a reference oxygen chamber serving as an oxygen reference source, a solid electrolyte body, and a solid electrolyte body. An electrode.

  Then, one electrode of the pair of electrodes is exposed in the measurement chamber, and the other electrode is exposed in the reference oxygen chamber so that it extends from the front end side exposed to the measurement target gas to the rear end side in the longitudinal direction. It has the structure extended along. Further, the inner electrode as one electrode and the surrounding electrode as the other electrode are both formed on the same surface of the solid electrolyte body.

  In particular, in this gas sensor element, in a plan view when the same surface is viewed from the vertical direction, the peripheral electrode is disposed on a part of the outer peripheral side of the inner electrode and is also positioned on one side in the width direction perpendicular to the longitudinal direction. It is arranged in a setting area excluding the projection area where the electrodes are projected.

  Further, in the opposite portion of the inner electrode facing the surrounding electrode, in a high temperature region that is equal to or higher than the median of the maximum value and the minimum value of the temperature gradient in the longitudinal direction in the inner electrode (that is, the temperature gradient when the gas sensor element is used). The length of the high temperature part which exists is 50% or more of the length of the opposing part. That is, the length of the high temperature portion of the opposing portion of the inner electrode is equal to or longer than the length of the lower temperature portion (low temperature portion).

  Therefore, even when the surrounding electrode is not provided in one projection region and the dimension in the width direction of the gas sensor element is reduced, the length of the high temperature portion having high electrochemical activity is longer than the length of the low temperature portion. Therefore, the internal resistance (that is, the internal resistance between the inner electrode and the surrounding electrode) can be sufficiently reduced.

Therefore, even if the electric current which flows between a pair of 2nd electrodes is small, the fall of the detection precision of specific gas can be suppressed.
That is, in the second aspect, when detecting a specific gas contained in the measurement target gas, it is possible to suppress a decrease in the detection accuracy of the specific gas, and to reduce the size and power consumption of the gas sensor element. Has an effect.

  (3) In the third aspect of the present invention, the first distance from one end in the width direction of the inner electrode to one end in the width direction of the gas sensor element is from the other end in the width direction of the inner electrode. It is shorter than the second distance to the other end in the width direction of the gas sensor element.

  In the third aspect, since the second distance is longer (that is, wider) than the first distance, a peripheral electrode is arranged in this wide region (second region), and the narrow region on the opposite side is arranged. In the (first region), no surrounding electrode can be arranged.

Thereby, since the width | variety of a gas sensor element can be narrowed, size reduction and power saving of a gas sensor element can be achieved.
Further, for example, when electrodes are formed by printing, the printing width has a certain limit, and printing cannot be suitably performed in a region having a very narrow width. However, in the third aspect, since the second distance is longer (wide) than the first distance, even if the overall width of the gas sensor element is narrowed, it is easy to print in the relatively wide second region by printing. A peripheral electrode can be formed.

  Here, the one end in the width direction of the inner electrode is the end closest to the one end in the width direction of the gas sensor element, and the other end in the width direction of the inner electrode is the gas sensor. This is the end closest to the other end in the width direction of the element (the same applies to the fourth aspect).

  (4) In the fourth aspect of the present invention, the periphery formed in the first region projected in the longitudinal direction from one end in the width direction of the inner electrode to one end in the width direction of the gas sensor element The dimension in the width direction of the electrode is the width of the surrounding electrode formed in the second region projected in the longitudinal direction from the other end in the width direction of the inner electrode to the other end in the width direction of the gas sensor element. Shorter than the direction dimension.

  In the fourth aspect, the width of the gas sensor element can be reduced by increasing the width of the peripheral electrode arranged in the second region and reducing the width of the peripheral electrode arranged in the first region (for example, 0). The gas sensor element can be reduced in size and power can be saved.

  (5) In the fifth aspect of the present invention, the peripheral electrode includes a long-side peripheral electrode portion extending in the width direction on the front end side or the rear end side of the inner electrode, and is connected to the long-side peripheral electrode portion. A width side peripheral electrode portion extending in the longitudinal direction is provided on the other side in the width direction of the inner electrode.

In the fifth aspect, the preferred shape of the surrounding electrode (L-shape in plan view) is illustrated.
(6) In the sixth aspect of the present invention, the peripheral electrode includes a long-side peripheral electrode portion extending in the width direction on each of the front end side and the rear end side of the inner electrode, and is connected to both the long-side peripheral electrode portions. And a width side peripheral electrode portion extending in the longitudinal direction on the other side in the width direction of the inner electrode.

  In the sixth aspect, a preferred shape of the surrounding electrode (a U shape in plan view) is illustrated. In this case, since the surrounding electrode can be set longer than in the fifth aspect, even a weak current can be detected with high accuracy. Therefore, the detection accuracy of the specific gas can be increased.

(7) In the seventh aspect of the present invention, the area of the surrounding electrode is equal to or greater than the area of the inner electrode.
Thereby, even a weak current can be detected with high accuracy, so that the detection accuracy of the specific gas can be increased.

  (8) A gas sensor according to an eighth aspect of the present invention is a gas sensor including a gas sensor element that detects a specific gas contained in a measurement target gas, and includes the gas sensor element according to the first to seventh aspects as a gas sensor element. Yes.

  This gas sensor can suppress a decrease in detection accuracy of a specific gas, and can reduce the size and power consumption of the gas sensor (by using a compact gas sensor element).

  According to the gas sensor element and the gas sensor of the present invention, it is possible to suppress a decrease in detection accuracy of a specific gas, and to achieve a remarkable effect that the gas sensor element can be reduced in size and power can be saved.

It is sectional drawing which shows the state which fractured | ruptured the NOx sensor of 1st Embodiment along the axial direction. It is a perspective view which shows the gas sensor element of 1st Embodiment. It is a perspective view which decomposes | disassembles and shows the gas sensor element of 1st Embodiment. It is explanatory drawing which fractures | ruptures the gas sensor element of 1st Embodiment in the thickness direction, and represents the internal structure etc. in the front end side. It is a top view which shows the inner side electrode and surrounding electrode which are arrange | positioned on the same surface of the solid electrolyte body in 1st Embodiment. It is a top view which expands and shows the inner side electrode and surrounding electrode which are arrange | positioned at the same surface of the solid electrolyte body in 1st Embodiment. It is explanatory drawing which shows the temperature distribution in the longitudinal direction of the gas sensor element of 1st Embodiment, the relationship between the temperature distribution, an inner side electrode, and a surrounding electrode etc. It is explanatory drawing which shows the relationship of the dimension etc. in planar view of the inner side electrode and surrounding electrode in 1st Embodiment. It is a top view which shows the inner side electrode and surrounding electrode which are arrange | positioned on the same surface of the solid electrolyte body in 2nd Embodiment. It is explanatory drawing which shows the temperature distribution in the longitudinal direction of the gas sensor element of 2nd Embodiment, the relationship between the temperature distribution, an inner side electrode, and a surrounding electrode etc. It is a top view which shows the inner side electrode and surrounding electrode which are arrange | positioned on the same surface of the solid electrolyte body in 3rd Embodiment. It is a graph which shows the temperature distribution in the longitudinal direction of the gas sensor element in 3rd Embodiment. It is explanatory drawing which fractures | ruptures the gas sensor element of 4th Embodiment in the thickness direction, and represents the internal structure etc. in the front end side. It is a top view which shows the inner side electrode and surrounding electrode which are arrange | positioned on the same surface of the solid electrolyte body in other embodiment. It is explanatory drawing of a prior art.

Embodiments to which the present invention is applied will be described below with reference to the drawings.
In the embodiment described below, a NOx sensor which is a kind of gas sensor is taken as an example. Specifically, it is a gas sensor mounted on an exhaust pipe in an automobile or various internal combustion engines, and a specific gas (nitrogen oxide: NOx) in an exhaust gas to be measured (that is, a gas having a higher temperature than the surrounding atmosphere). A description will be given by taking as an example a NOx sensor configured by assembling a gas sensor element (detection element) to be detected.

[1. First Embodiment]
[1-1. overall structure]
First, the overall configuration of the NOx sensor in which the gas sensor element of the first embodiment is used will be described with reference to FIG. 1 is the front end side of the NOx sensor, and the upper direction in FIG. 1 is the rear end side of the NOx sensor.

  As shown in FIG. 1, the NOx sensor 1 according to the first embodiment includes a cylindrical metal shell 5 having a screw portion 3 formed on the outer surface for fixing to an exhaust pipe, and an axis O direction (NOx sensor 1 Plate-shaped gas sensor element 7 extending in the longitudinal direction of FIG. 1, a cylindrical ceramic sleeve 9 arranged to surround the circumference of the gas sensor element 7 in the radial direction, and an insertion penetrating in the direction of the axis O The first separator 13 is disposed in a state where the inner wall surface of the hole 11 surrounds the periphery of the rear end portion of the gas sensor element 7, and six are disposed between the gas sensor element 7 and the first separator 13 (in FIG. 1). Only two connection terminals 15 are shown.

  As will be described in detail later, the gas sensor element 7 is formed in a rectangular parallelepiped shape (plate shape) extending in the longitudinal direction, and a specific gas (here, exhaust gas) included in the measurement target gas (here, exhaust gas) is formed on the tip side thereof. NOx) is provided. In addition, the gas sensor element 7 has electrode pads 25 on the first main surface 21 and the second main surface 23 that are in a positional relationship of the front and back of the outer surface on the rear end side (upper side in FIG. 1: rear end portion in the longitudinal direction). 26, 27, 28, 29, and 30 (refer to FIGS. 2 and 3 for details) are formed.

  Different connection terminals 15 are electrically connected to the electrode pads 25 to 30 of the gas sensor element 7, respectively, and the connection terminals 15 are electrically connected to lead wires 35 disposed inside the sensor from the outside. ing. As a result, a current path for current flowing between the external device to which the lead wire 35 is connected and the electrode pads 25 to 30 is formed.

  The metal shell 5 has a through-hole 37 that penetrates in the direction of the axis O, and has a substantially cylindrical shape having a shelf 39 that protrudes radially inward of the through-hole 37. The metal shell 5 is disposed in the through hole 37 in a state in which the detection unit 17 is arranged on the front side of the through hole 37 and the electrode pads 25 to 30 are arranged on the rear side of the through hole 37. The inserted gas sensor element 7 is held.

  An annular ceramic holder 41, talc rings 43 and 45, and the above-described ceramic sleeve 9 are arranged in this order in the through hole 37 of the metal shell 5 so as to surround the periphery of the gas sensor element 7 in the radial direction. It is laminated from the 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, between the ceramic holder 41 and the shelf 39 of the metal shell 5, 45 and a metal holder 51 for holding the ceramic holder 41 are arranged. Note that the rear end portion 47 of the metal shell 5 is crimped so as to press the ceramic sleeve 9 toward the front end side via a crimping packing 49.

  Further, a metal double protector 55 (for example, stainless steel) covering the protruding portion of the gas sensor element 7 is attached to the outer periphery of the distal 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 on the rear end side of the metal shell 5. Further, a grommet 59 in which six lead wire insertion holes 61 (only two are shown in FIG. 1) is formed in the opening on the rear end side of the outer cylinder 57. Six lead wires 35 (two are shown in FIG. 1) electrically connected to the electrode pads 25 to 30 are inserted into the six lead wire insertion holes 61.

  A flange 63 is formed on the outer periphery of the first separator 13, and the flange 63 is fixed to the outer cylinder 57 via a holding member 65. A second separator 67 that is sandwiched between the first separator 13 and the grommet 59 is disposed on the rear end side of the first separator 13. The rear end side of the connection terminal 15 is inserted into the second separator 67.

[1-2. Configuration of gas sensor element]
Next, the configuration of the gas sensor element 7 will be described in detail with reference to FIGS.
In FIG. 2, the lower direction is the front end side of the gas sensor element 7, and the upper direction is the rear end side of the gas sensor element 7. In FIG. 3, the left direction is the front end side of the gas sensor element 7, and the right direction is the rear end side of the gas sensor element 7. In FIG. 4, the left direction is the front end side of the gas sensor element 7, and the right direction is the rear end side of the gas sensor element 7. Further, in FIG. 4, illustration of an intermediate position in the longitudinal direction of the gas sensor element 7 is omitted, and an electrical connection state between the gas sensor element 7 and an external device (control unit 110) is schematically shown.

  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 direction of the axis O of the gas sensor. 2 is a stacking direction perpendicular to the longitudinal direction, and the X-axis direction is a width direction perpendicular to the longitudinal direction and the stacking direction.

  The gas sensor element 7 is formed in a rectangular parallelepiped shape (plate shape) extending in the longitudinal direction, and a plate-like element portion 71 extending in the longitudinal direction and a plate-like heater 73 extending in the longitudinal direction are laminated. It is configured. The gas sensor element 7 includes a detection unit 17 that detects a specific gas contained in the measurement target gas on the tip side.

  As shown in an exploded view in FIG. 3, the gas sensor element 7 is disposed on one side in the stacking direction (upper side in FIG. 3), and extends in the longitudinal direction to a plate-like element portion 71 and the opposite side of the element portion 71. A plate-like heater 73 disposed on the back side and extending in the longitudinal direction.

In addition, the element unit 71 includes a first pump cell 81, an oxygen concentration detection cell 82, and a second pump cell 83, as will be described later.
Specifically, the element unit 71 has a structure in which an insulator 84e, a first solid electrolyte body 81a, an insulator 84a, a second solid electrolyte body 82a, an insulator 84b, and a third solid electrolyte body 83a are stacked in this order. . The heater 73 has a structure in which insulators 84c and 84d are stacked in this order. Each of these layers is laminated in a direction perpendicular to the longitudinal direction of the gas sensor element 7. Each solid electrolyte body 81 a, 82 a, 83 a has a plate shape extending in the longitudinal direction of the gas sensor element 7.

  A first measurement chamber 86 is formed between the first solid electrolyte body 81a and the second solid electrolyte body 82a. The front end side region of the first measurement chamber 86 is connected to the outside via two first diffusion resistors 85a. A measurement target gas (exhaust gas) that is outside air is introduced into the gas sensor element 7 from the outside via the first diffusion resistor 85a. In the rear end region, the first measurement chamber 86 is connected to the second measurement chamber 88 formed in the insulator 84b through a through hole 88a formed in the second solid electrolyte body 82a.

  A heating resistor 91 formed of a conductor such as tungsten is provided between the two insulators 84c and 84d. The heating resistor 91 is provided as a part of the heater 73.

  The heater 73 heats up the gas sensor element 7 (particularly, the element unit 71) to a predetermined activation temperature when the heating resistor 91 generates heat by the electric power supplied from the outside, and conducts oxygen ions in the solid electrolyte body. Is used to stabilize the operation.

  Note that most of the heating resistor 91 is disposed on the tip side of the inner electrode 93. Therefore, when heating by the heating resistor 91, the temperature on the tip side becomes higher than the inner electrode 93. That is, the temperature peak in the longitudinal direction of the gas sensor element 7 is on the tip side from the inner electrode 93 (see FIG. 7 described later).

  In the first embodiment, the solid electrolyte bodies 81a, 82a, and 83a are each formed using zirconia having oxygen ion conductivity as a main component. The insulators 84a to 84e are formed using alumina as a main component, and are formed dense enough to prevent permeation (circulation) of fluid such as gas. The first diffusion resistor 85a is formed using a porous material such as alumina, and gas can be circulated. The main component means that “the content of the main material in the ceramic layer is 50 wt% or more”. For example, the solid electrolyte body contains 50 wt% or more of zirconia.

  Six layers 84e, 81a, 82a, 83a, 84c, 84d of the eight layers of the solid electrolyte body and the insulator are each formed using a raw material sheet (for example, zirconia, alumina, or the like). Ceramic sheet). The two insulators 84a and 84b are formed by screen printing on a ceramic sheet. And the gas sensor element 7 is formed by baking the laminated body obtained by laminating | stacking each layer before baking.

Next, the first pump cell 81, the oxygen concentration detection cell 82, and the second pump cell 83 will be described.
The first pump cell 81 includes a first solid electrolyte body 81a and a pair of electrodes (an inner first electrode 81c and an outer first electrode 81b) disposed so as to sandwich the first solid electrolyte body 81a.

  The inner first electrode 81 c faces the first measurement chamber 86. The inner first electrode 81c and the outer first electrode 81b are both formed mainly of platinum. The outer first electrode 81b is covered with a porous portion 81d (for example, alumina) embedded in a portion of the insulator 84e that faces the outer first electrode 81b. The porous portion 81d is configured to allow gas (for example, oxygen) to pass therethrough.

  The oxygen concentration detection cell 82 includes a second solid electrolyte body 82a, and an oxygen inner electrode 82b and a reference electrode 82c arranged so as to sandwich the second solid electrolyte body 82a. Both the oxygen inner electrode 82b and the reference electrode 82c are formed mainly of platinum.

  A reference oxygen chamber 87 as a space portion penetrating in the thickness direction of the insulator 84b is formed in a portion of the insulator 84b in contact with the reference electrode portion 82c. The reference oxygen chamber 87 is formed in, for example, an L shape when viewed in the thickness direction of the insulator 84b (plan view), and a porous portion is formed in a region facing the third solid electrolyte body 83a therein. 87a is arranged, and other regions are formed as cavities. The oxygen inner electrode 82b and the reference electrode 82c are, for example, L-shaped so as to have the same shape as the reference oxygen chamber 87 in plan view.

  Further, a second measurement chamber 88 as a space portion penetrating in the thickness direction of the insulator 84b is formed on the rear end side of the reference oxygen chamber 87 in the insulator 84b. The second measurement chamber 88 is, for example, rectangular in plan view.

  Note that oxygen is sent from the first measurement chamber 86 to the reference oxygen chamber 87 via the oxygen concentration detection cell 82 by passing a predetermined weak constant current through the oxygen concentration detection cell 82. The oxygen concentration in the reference oxygen chamber 87 is maintained at a predetermined concentration. Thereby, the reference oxygen chamber 87 is used as a reference for the oxygen concentration.

  The second pump cell 83 includes a third solid electrolyte body 83a and a pair of electrodes (an inner electrode 93 and a surrounding electrode 95) disposed on the surface of the third solid electrolyte body 83a facing the second measurement chamber 88. ing. Both the inner electrode 93 and the surrounding electrode 95 are formed with platinum as a main component.

  The peripheral electrode 95 is formed on the surface of the third solid electrolyte body 83a facing the insulator 84b, and is disposed in a region corresponding to the reference oxygen chamber 87 of the insulator 84b. The surrounding electrode 95 faces the reference oxygen chamber 87 so as to face the reference electrode 82c. The inner electrode 93 is formed on the surface of the third solid electrolyte body 83a that faces the insulator 84b, and is disposed in a region corresponding to the second measurement chamber 88 of the insulator 84b.

As will be described later, the surrounding electrode 95 is, for example, an L shape similar to the reference oxygen chamber 87 in plan view, and the inner electrode 93 is, for example, a rectangle similar to the second measurement chamber 88 in plan view. .
Each of the electrodes 81b, 81c, 82b, 82c, 93, and 95 is formed in a porous shape so that a gas can be circulated therein in order to maintain a good electrode reaction. That is, it is formed in a porous shape that can satisfactorily form a three-phase interface where the gas of the measurement target gas (gas phase such as oxygen or NOx), the electrode (catalyst phase), and the solid electrolyte (oxygen ion conduction phase) are in contact. Has been.

  Three electrode pads 25, 26, and 27 are formed on the outer surface on the rear end side of the insulator 84e. In addition, three electrode pads 28, 29, and 30 are formed on the outer surface on the rear end side of the insulator 84d. Each of the electrode pads 25 to 30 is formed, for example, by printing and baking metallized ink such as Pt on the insulators 84e and 84d.

Each electrode 81b, 81c, 82b, 82c, 93, 95 and the heating resistor 91 are electrically connected to corresponding electrode pads 25-30 by wiring units L1-L6.
Specifically, the first electrode pad 25 is electrically connected to the outer first electrode 81b by the first wiring unit L1. The second electrode pad 26 is electrically connected to the reference electrode 82c by the second wiring unit L2. The third electrode pad 27 is electrically connected to the inner first electrode 81c, the oxygen inner electrode 82b, and the inner electrode 93 by the third wiring unit L3. The fourth electrode pad 30 is electrically connected to the surrounding electrode 95 by the fourth wiring unit L4.

  The first heater electrode pad 28 is electrically connected to the heating resistor 91 by the first heater wiring unit L5. The second heater electrode pad 29 is electrically connected to the heating resistor 91 by the second heater wiring unit L6. In addition, the wiring units L1-L6 are provided by printing the paste which has platinum as a main component and contains ceramic (for example, alumina).

  The first wiring unit L1 includes a first lead portion 101a and a first through-hole conductor portion 101b. The first lead portion 101a extends in the longitudinal direction from the outer first electrode 81b along the first solid electrolyte body 81a. The first through-hole conductor portion 101b has one end connected to the first electrode pad 25 and the other end connected to the first lead portion 101a.

  The second wiring unit L2 includes a second lead portion 102a and a second through-hole conductor portion 102b. The second lead portion 102a extends in the longitudinal direction from the reference electrode 82c toward the rear end side along the second solid electrolyte body 82a. The second through-hole conductor portion 102b has one end connected to the second electrode pad 26 and the other end connected to the second lead portion 102a.

  The third wiring unit L3 includes a third lead portion 103a, a fourth lead portion 103b, a fifth lead portion 103c, and a third through-hole conductor portion 103d. The third lead portion 103a extends in the longitudinal direction from the inner first electrode 81c toward the rear end side along the first solid electrolyte body 81a. The fourth lead portion 103b extends in the longitudinal direction from the oxygen inner electrode 82b toward the rear end side along the second solid electrolyte body 82a. The fifth lead portion 103c extends in the longitudinal direction from the inner electrode 93 toward the rear end side along the third solid electrolyte body 83a.

  The third through-hole conductor portion 103d has one end connected to the third electrode pad 27, an intermediate portion connected to the third lead portion 103a and the fourth lead portion 103b, and the other end connected to the fifth lead portion 103c. The

  The inner first electrode 81c, the oxygen inner electrode 82b, and the inner electrode 93 are electrically connected to the common third electrode pad 27. The third electrode pad 27 is connected to the ground potential of the control unit 110 (see FIG. 4).

  The fourth wiring unit L4 includes a sixth lead portion 104a and a fourth through-hole conductor portion 104b. The sixth lead portion 104a extends in the longitudinal direction from the peripheral electrode 95 toward the rear end side along the third solid electrolyte body 83a. The fourth through-hole conductor portion 104b has one end connected to the fourth electrode pad 30 and the other end connected to the sixth lead portion 104a.

  The first heater wiring unit L5 includes a first heater lead portion 105a and a first heater through-hole conductor portion 105b. The first heater lead portion 105a extends along the longitudinal direction from the heating resistor 91 toward the rear end side. The first heater through-hole conductor portion 105 b has one end connected to the first heater lead portion 105 a and the other end connected to the first heater electrode pad 28.

  The second heater wiring unit L6 includes a second heater lead portion 106a and a second heater through-hole conductor portion 106b. The second heater lead portion 106a extends along the longitudinal direction from the heating resistor 91 toward the rear end side. The second heater through-hole conductor portion 106 b has one end connected to the second heater lead portion 106 a and the other end connected to the second heater electrode pad 29.

  Further, as described above, each of the electrodes 81b, 81c, 82b, 82c, 93, 95 is a porous electrode mainly composed of platinum, and each of the electrodes 81b, 81c, 82b, 82c, 93, 95 includes The first to sixth lead portions 101a, 103a, 103b, 102a, 103c, and 104a are connected so that a part of the tip side (left side in FIG. 3) slightly overlaps (the overlapping portions are Not shown).

  The first to sixth lead portions 101a, 103a, 103b, 102a, 103c, and 104a are mainly composed of platinum, but the composition thereof is different from that of each of the electrodes 81b, 81c, 82b, 82c, 93, and 95. . Specifically, among the first to sixth lead portions 101a, 103a, 103b, 102a, 103c, and 104a, 101a, 103a, 103b, and 103c have a smaller amount of binder than the electrode paste, and the dense lead portions are formed. Forming. On the other hand, 102a and 104a are formed using the same paste as the electrode paste.

[1-3. Operation of gas sensor element]
Next, an example of the operation of the gas sensor element 7 will be described.
As shown in FIG. 4, first, when the control unit 110 is activated by starting the engine, the control unit 110 supplies power to the heater 73. The heater 73 heats the first pump cell 81, the oxygen concentration detection cell 82, and the second pump cell 83 to the activation temperature.

  When each of the cells 81 to 83 is heated to the activation temperature, the control unit 110 causes a current (first pump current Ip1) to flow through the first pump cell 81. Accordingly, the first pump cell 81 moves the oxygen between the inner first electrode 81c and the outer first electrode 81b via the first solid electrolyte body 81a, thereby measuring the measurement object flowing into the first measurement chamber 86. Pumps oxygen in and out of gas (exhaust gas).

  The controller 110 controls the first pump current Ip1 energized in the first pump cell 81 so that the interelectrode voltage (inter-terminal voltage) of the oxygen concentration detection cell 82 becomes a constant voltage V1 (for example, 425 mV). The voltage of the oxygen concentration detection cell 82 is a value corresponding to the oxygen concentration in the oxygen inner electrode 82b with reference to the oxygen concentration in the reference oxygen chamber 87. By this control, the oxygen concentration in the first measurement chamber 86 is adjusted to the extent that NOx is not decomposed.

  The measurement target gas whose oxygen concentration is adjusted in the first measurement chamber 86 further flows toward the second measurement chamber 88. The controller 110 applies an interelectrode voltage (interterminal voltage) to the second pump cell 83. This voltage is set to a constant voltage such that the NOx gas in the measurement target gas is decomposed into oxygen and nitrogen gas (a voltage higher than the control voltage value of the oxygen concentration detection cell 82, for example, 450 mV). Thereby, NOx in the measurement target gas is decomposed into nitrogen and oxygen.

  A current (second pump current Ip2) flows through the second pump cell 83 so that oxygen generated by the decomposition of NOx is pumped from the second measurement chamber 88, and the control unit 110 detects the second pump current Ip2. Since there is a proportional relationship between the second pump current Ip2 and the NOx concentration, the NOx concentration in the measurement target gas can be detected by detecting the current value of the second pump current Ip2.

  The gas sensor element 7 is connected to an external device (control unit 110) via the connection terminal 15 and the lead wire 35. The control unit 110 supplies heat to the heater 73 and transmits / receives signals to / from the cells of the element unit 71 (first pump cell 81, oxygen concentration detection cell 82, second pump cell 83). The gas sensor element 7 is controlled. In the first embodiment, the control unit 110 is provided as an electronic circuit formed using an operational amplifier or the like. The control unit 110 may be formed using a computer having a CPU, a memory, and the like.

[1-4. Configuration of second pump cell]
Next, the structure of the 2nd pump cell 83 which is the principal part of this 1st Embodiment is demonstrated.
As can be seen from FIGS. 3 and 4, the second pump cell 83 includes a third solid electrolyte body 83a and a pair of electrodes (inner side) disposed on the surface of the third solid electrolyte body 83a facing the second measurement chamber 88. The electrode 93 and the surrounding electrode 95 are provided, and the inner electrode 93 and the surrounding electrode 95 are both formed on the same surface of the third solid electrolyte body 83a.

  As shown in an enlarged view in FIG. 5, the inner electrode 93 is rectangular in the plan view when the same surface is viewed from the vertical direction, and the peripheral electrode 95 is formed on two adjacent sides of the inner electrode 93 (that is, the upper side and the left side). Along the inner electrode 93 (that is, the outer periphery thereof), an L-shape is disposed at a predetermined interval.

Incidentally, the distance between the peripheral electrode 95 and the inner electrode 93, for example, a certain range of 0.2 to 0.9 mm (e.g. 0.4 mm), the area around the electrode 95 (e.g., 1.3 mm ^2), the inner It is larger than the area of the electrode 93 (for example, 1.1 mm ² ).

  Specifically, the peripheral electrode 95 includes a rectangular long-side peripheral electrode portion 95a extending in the width direction (vertical direction in FIG. 5) on the distal end side (left side in FIG. 5) of the inner electrode 93. Further, a rectangular shape extending in the longitudinal direction (left-right direction in FIG. 5) on the other side in the width direction of the inner electrode 93 so as to be connected to the other end (upper side in FIG. 5) of the long-side peripheral electrode portion 95a. A width side peripheral electrode portion 95b is provided.

  The peripheral electrode 95 is not formed in the projection region TR in which the inner electrode 93 is projected on one side (downward in FIG. 5) in the width direction of the inner electrode 93. In other words, the peripheral electrode 95 is disposed on a part of the outer peripheral side of the inner electrode 93, and the projection region TR in which the inner electrode 93 is projected onto one of the width directions perpendicular to the longitudinal direction (lower side in FIG. 5) It is arranged in the setting area SR excluding. Here, as shown in FIG. 5, the peripheral electrode 95 is arranged in a part of the setting region SR excluding the projection region TR in the periphery of the inner electrode 93.

  In other words, the setting region SR is obtained by removing the projection region TR from a range surrounding the entire circumference of the inner electrode 93 (that is, a range of 360 degrees in plan view). Here, a part of the setting region SR is A peripheral electrode 95 is arranged in an L shape. For example, the setting region SR does not include a range where the fifth lead portion 103c is formed.

Further, as shown in FIG. 6, the outer periphery of the inner electrode 93 includes a facing portion TB (portion indicated by a thick line in FIG. 6) that faces the surrounding electrode 95. Here, the facing portion TB will be described.
When the outer peripheral portion of the inner electrode 93 is projected in the longitudinal direction (with the maximum dimension in the width direction) (for example, when projected in the direction of the leftward arrow in FIG. 6), the surrounding electrode 95 exists at the projection destination. In this case, it is assumed that the outer peripheral portion of the projection source is a facing portion TB of the inner electrode 93.

  Similarly, when the outer peripheral portion of the inner electrode 93 is projected onto the other side in the width direction (with the maximum dimension in the longitudinal direction) (for example, when projected in the upward arrow direction in FIG. 6), In the case where the electrode 95 exists, the outer peripheral portion of the projection source is set as a facing portion TB of the inner electrode 93. In other words, if either one of the conditions is satisfied, the counter part TB is set.

Therefore, in this case, the upper side and the left side of the rectangular inner electrode 93 are the facing portion TB.
Note that the length of the facing portion TB is the length of the outer periphery of the inner electrode 93 at the facing portion TB. Further, depending on the shape of the outer periphery of the inner electrode 93, the facing portion TB may partially overlap when projected in the longitudinal direction and when projected to the other in the width direction. In this case, when obtaining the length of the facing portion TB, it can be obtained by removing one of the overlapping portions.

  Furthermore, in the first embodiment, as shown in FIG. 7, the maximum value (Max) and the minimum value of the temperature gradient in the longitudinal direction in the inner electrode 93 when the gas sensor element 7 is used among the above-described facing portions TB. The length of the high-temperature portion KB existing in the high-temperature region KR equal to or greater than the median {(Max + Min) / 2} with (Min) is 50% or more (exceeded here) of the entire length of the opposing portion TB.

Here, the temperature gradient described above will be described.
Normally, when a gas sensor (here, NOx sensor) 1 is used to detect a specific gas (for example, NOx) in a measurement target gas (for example, exhaust gas) (for example, when NOx concentration is detected), each solid of the gas sensor element 7 is detected. Electrolytes 81a, 82b, 83a (at least the portions where the electrodes of the solid electrolyte bodies 81a, 82b, 83a are disposed) are at or above a predetermined activation temperature (that is, the cells 81, 82, 83 can be operated). This is done when the temperature is over).

  For example, when heated by the heater 73 or when heated by an exhaust gas having a temperature higher than the ambient air, the NOx concentration is detected when the activation temperature is exceeded.

  When the activation temperature is equal to or higher than the activation temperature (for example, 600 ° C.), the gas sensor element 7 has a temperature gradient (temperature distribution) as shown in the upper diagram of FIG. Note that the temperature distribution after activation is almost the same temperature distribution if there is no influence of disturbance.

  That is, when the NOx concentration in the exhaust gas is detected by the NOx sensor 1, the temperature of the portion where the heating resistor 91 is arranged in the gas sensor element 7 is high. The temperature becomes higher than the rear end side.

  Therefore, when the inner electrode 93 is divided into the front end side (left side in FIG. 7) and the rear end side by the central line CL indicating the median value, the front end side portion is the high temperature region KR, and among the opposing portions TB, The portion included in the high temperature region KR (the outer peripheral side of the L-shaped hatched portion in FIG. 6) is the high temperature portion KB. Further, the portion on the rear end side from the remaining central line CL is a low temperature portion TE that is not the high temperature portion KB. Accordingly, the outer circumference of the high temperature portion KB is longer than the outer circumference of the low temperature portion TE.

  7 is a temperature distribution along the longitudinal direction of the gas sensor element 7, more specifically, a temperature distribution along the longitudinal direction at the center in the width direction. For example, an infrared thermography or the like is used. Can be sought. Further, the temperature distribution in the width direction of the gas sensor element 7 is substantially constant (that is, there is not much temperature change).

  Further, in the first embodiment, as shown in FIG. 8, the first distance from one end in the width direction of the inner electrode 93 (downward in FIG. 8) to one end in the width direction of the gas sensor element 7. (A1) is set to be shorter than the second distance (A2) from the other end in the width direction of the inner electrode 93 (upper side in FIG. 8) to the other end in the width direction of the gas sensor element 7. .

The first distance (A1) is, for example, 0.7 mm in the range of 0.4 to 1.0 mm, and the second distance (A2) is, for example, 1. in the range of 1.0 to 2.0 mm. 6 mm.
Further, the first dimension B1 shown in FIG. 8 (that is, the dimension in which the peripheral electrode 95 protrudes below the inner electrode 93 in FIG. 8: 0 in the first embodiment) is the second dimension B2 (that is, the peripheral electrode 95 is the inner electrode). 93 is set so as to be shorter than the dimension protruding upward in FIG.

  Specifically, when a portion from one end portion in the width direction of the inner electrode 93 to one end portion in the width direction of the gas sensor element is projected in the longitudinal direction (left and right direction in FIG. 8), the projected range is The first dimension B1 in the width direction of the peripheral electrode 95 formed in one region R1 is a lengthwise direction from the other end portion in the width direction of the inner electrode 93 to the other end portion in the width direction of the gas sensor element 7. Is set to be shorter than the second dimension B2 in the width direction of the peripheral electrode 95 formed in the second region R2 which is the projected range.

  The first dimension (B1) is, for example, 0 mm in the range of 0.6 mm or less, and the second dimension (B2) is, for example, 1.0 mm in the range of 0.7 to 1.3 mm. Here, the first dimension (B1) may be a negative value because the case where the surrounding electrode 95 is positioned above the inner electrode 93 in FIG.

[1-5. effect]
As described above, the gas sensor element 7 in the NOx sensor 1 of the present embodiment includes the inner electrode 93 and the surrounding electrode 95 as a pair of electrodes in the second pump cell 83. The inner electrode 93 and the surrounding electrode 95 are both formed on the same surface of the third solid electrolyte body 83a.

  The peripheral electrode 95 is disposed in the setting region SR excluding one projection region TR in the width direction perpendicular to the longitudinal direction of the inner electrode 93, that is, in one projection region TR in the width direction. Since the surrounding electrode 95 is not disposed, the dimension in the width direction of the gas sensor element 7 can be reduced. Thereby, size reduction and power saving of the gas sensor element 7 can be achieved.

  Further, among the opposing portions TB of the inner electrode 93 facing the peripheral electrode 95, the center value of the maximum value and the minimum value of the temperature gradient in the longitudinal direction in the inner electrode 93 when the gas sensor element 7 is used is greater than or equal to the front end side. The length of the high temperature portion KB existing in the high temperature region KR is 50% or more of the length of the opposing portion TB (exceeding here). That is, the length of the high temperature portion KB in the facing portion TB of the inner electrode 93 is longer than the length of the low temperature portion TE at a lower temperature.

Therefore, even when the peripheral electrode 95 is not provided in one projection region TR and the dimension in the width direction of the gas sensor element 7 is reduced, the internal resistance can be sufficiently reduced.
Therefore, even if the current flowing between the inner electrode 93 and the surrounding electrode 95 is small as in the NOx sensor 1, it is possible to suppress a decrease in NOx detection accuracy.

That is, in the first embodiment, it is possible to suppress a decrease in the detection accuracy of NOx, and to achieve a remarkable effect that the gas sensor element 7 can be reduced in size and power can be saved.
In the first embodiment, the second distance A2 is longer than the first distance A1 (that is, the gap between the other end of the inner electrode 93 and the other end of the gas sensor element 7 in the width direction is wide). Therefore, the peripheral electrode 95 can be easily formed in this wide region (second region R2) by printing or the like. By providing the peripheral electrode 95 in the second region R2, it is possible to prevent the peripheral electrode 95 from being provided in a narrow region (first region R1) opposite to the second region R2.

Thereby, since the width | variety of the gas sensor element 7 can be narrowed, the size reduction and power saving of the gas sensor element 7 can be achieved also from this point.
The print width has a certain limit, and printing cannot be suitably performed in a region where the width is too narrow. However, in the first embodiment, since the second distance A2 is long (wide), even if the entire width of the gas sensor element 7 is narrowed, it is easy to print in the relatively wide second region by printing. A peripheral electrode 95 can be formed.

  Furthermore, in the first embodiment, the gas sensor is formed by increasing the width of the peripheral electrode 95 disposed in the second region R2 and decreasing the width of the peripheral electrode 95 disposed in the first region R1 (for example, 0). Since the width of the element 7 can be reduced, the gas sensor element 7 can be reduced in size and power can be saved from this point.

In the first embodiment, since the area of the peripheral electrode 95 is equal to or larger than the area of the inner electrode 93, even a weak current can be detected with high accuracy.
[1-6. Correspondence with Claims]
Here, the correspondence relationship of the words in the claims and the first embodiment will be described.

  NOx sensor 1, gas sensor element 7, first pump cell 81, solid electrolyte bodies 81a, 83a, first electrodes 81b, 81c, first measurement chamber 86, second measurement chamber 88, second pump cell 83, The inner electrode 93, the peripheral electrode 95, the long side peripheral electrode portion 95a, and the width side peripheral electrode portion 95b are respectively a gas sensor, a gas sensor element, a first pump cell, a solid electrolyte body, a first electrode, and a first measurement chamber of the present invention. This corresponds to an example of the second measurement chamber, the second pump cell, the inner electrode, and the surrounding electrode.

[2. Second Embodiment]
Next, the second embodiment will be described, but the description of the same configuration as the first embodiment will be omitted or simplified. In addition, the same structure as 1st Embodiment is demonstrated using the same number.

As shown in FIGS. 9 and 10, the gas sensor element 121 of the second embodiment is different from the first embodiment in the shape of the peripheral electrode 123.
Specifically, the peripheral electrode 123 is U-shaped in plan view, and includes long-side peripheral electrode portions 123a and 123b extending in the width direction on the front end side (left side in FIG. 9) and the rear end side of the inner electrode 93, respectively. In addition, a width-side peripheral electrode portion 123c extending in the longitudinal direction is provided on the other side in the width direction of the inner electrode 93 (upward in FIG. 9) so as to be connected to both the long-side peripheral electrode portions 123a and 123b.

  The second embodiment has the same effect as the first embodiment, and the opposing portion TB (the thick line portion in FIG. 9) of the inner electrode 93 can be set longer than the first embodiment, so that the detection accuracy is further improved. There is an advantage.

[3. Third Embodiment]
Next, the third embodiment will be described, but the description of the same configuration as the first embodiment will be omitted or simplified. In addition, the same structure as 1st Embodiment is demonstrated using the same number.

As shown in FIG. 11, the gas sensor element 131 of the third embodiment is different from the first embodiment in the shapes of the peripheral electrode 133 and the inner electrode 135.
Specifically, the peripheral electrode 133 has an arcuate shape in plan view, and a long-side peripheral electrode portion 133a extending in the width direction on the distal end side (left side in FIG. 11) of the inner electrode 135 and the inner electrode 93 A width-side peripheral electrode portion 133b extending in the longitudinal direction on the other side in the width direction (upper side in FIG. 11), and an intermediate electrode having a quarter circle shape connecting the longitudinal-side peripheral electrode portion 133a and the width-side peripheral electrode portion 133b A portion 133c is provided.

Further, the inner electrode 135 has a substantially rectangular shape with a long longitudinal direction, and the surrounding corners (vertices) are smoothly curved.
Furthermore, the high temperature portion KB (the outer peripheral side of the shaded portion in FIG. 11) is the tip side from the center line CL. Here, as shown in FIG. 12, the center line CL is a median value between 691 ° C. and 642 ° C., and the ratio (the length of the outer peripheral portion) to the facing portion TB (thick line portion in FIG. 11) of the high temperature portion KB. The ratio) is 64.7%.

  In the third embodiment, a portion where the distance between the inner electrode 135 and the surrounding electrode 133 is constant is employed as the facing portion TB of the inner electrode 135 (that is, a range in which a sufficient current flows).

The third embodiment has the same effects as the first embodiment.
[4. Fourth Embodiment]
Next, the fourth embodiment will be described, but the description of the same configuration as the first embodiment will be omitted or simplified. In addition, the same structure as 1st Embodiment is demonstrated using the same number.

  The gas sensor of the fourth embodiment is an oxygen sensor that detects the oxygen concentration by a so-called limit current method. As shown in FIG. 13, the gas sensor element 141 used for the oxygen sensor is different from that of the first embodiment. The structure of the element 141 itself is different.

  Specifically, the gas sensor element 141 is a long element extending in the left-right direction in FIG. 13, for example, insulators 143 and 145 mainly composed of alumina, and a solid electrolyte body 147 mainly composed of zirconia, for example ( It has a structure in which insulators 149 and 151 mainly comprising alumina, for example, are laminated.

A heating resistor 152 is disposed between the two insulators 149 and 151.
The insulator 143 is provided with a through hole 155 filled with a porous body 153. The insulator 145 is provided with a measurement chamber 157 that communicates with the through hole 155 and into which a measurement target gas (for example, exhaust gas) is introduced, and a reference oxygen chamber 159 that serves as an oxygen reference source.

  A pair of electrodes 161 and 163 are provided on the same surface of the solid electrolyte body 147. Among these, the surrounding electrode 161 which is one electrode is exposed to the measurement chamber 157 and the inner electrode 163 which is the other electrode. Is exposed to the reference oxygen chamber 159.

The shape, arrangement, and the like of the peripheral electrode 161 and the inner electrode 163 are the same as those in the first embodiment.
In the fourth embodiment, for example, a voltage is applied between the peripheral electrode 161 and the inner electrode 163, a pump current is caused to flow between the peripheral electrode 161 and the inner electrode 163, and oxygen is pumped by the pump current. (For example, oxygen is moved from the measurement chamber 157 to the reference oxygen chamber 159).

As is well known, the oxygen concentration is detected from the value (limit current) at which the pump current during the pumping becomes constant.
Although the gas component to be detected is different from that of the first embodiment, the fourth embodiment can suppress a decrease in detection accuracy of the gas concentration and can reduce the size and power of the apparatus as in the first embodiment. Can be planned.

  Separately from this, based on the electromotive force generated between the surrounding electrode 161 and the inner electrode 163 due to the oxygen concentration difference between the oxygen concentration in the measurement chamber 157 and the oxygen concentration in the reference oxygen chamber 159. As is well known, it is also possible to detect the oxygen concentration.

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

  (1) For example, as shown in FIG. 14, one end (downward in FIG. 14) of the peripheral electrode 171 protrudes toward one end of the gas sensor element 175 rather than one end of the inner electrode 173. It may be.

Also in this case, the relationship of the first dimension B1 <the second dimension B2 and the first distance A1 <the second distance A2 is established.
(2) Moreover, in each said embodiment, although the solid electrolyte body extended from the front end side of a gas sensor element to the rear end side is used, you may provide a solid electrolyte body in the position in which each electrode is provided. The solid electrolyte body provided with the well-known electrode and the inner electrode is an integral one.

That is, for example, an insulator mainly composed of alumina may be used as the substrate, and the solid electrolyte body may be embedded in a part of the insulator.
(3) In addition, it is also possible to combine the component of each embodiment mentioned above suitably.

DESCRIPTION OF SYMBOLS 1 ... NOx sensor 7, 141 ... Gas sensor element 81 ... 1st pump cell 81a, 82a, 83a, 147 ... Solid electrolyte body 81b, 81c ... 1st electrode 86 ... 1st measurement chamber 88 ... 2nd measurement chamber 88 ... 2nd pump cell 93, 161 ... Inner electrode 95, 123, 163 ... Peripheral electrode 95a, 123a, 123b ... Longitudinal peripheral electrode part 95b, 123c ... Width side peripheral electrode part 157 ... Measurement chamber 159 ... Reference oxygen chamber A1 ... First distance A2 ... 2nd distance B1 ... 1st dimension B2 ... 2nd dimension R1 ... 1st area | region R2 ... 2nd area | region

Claims (8)

A first measurement chamber into which a measurement target gas is introduced;
A second measurement chamber into which the measurement target gas into which oxygen has been pumped or pumped in the first measurement chamber is introduced;
A solid electrolyte body and a pair of first electrodes formed on the solid electrolyte body, wherein one electrode of the pair of first electrodes is exposed to the first measurement chamber; A first pump cell for pumping or pumping oxygen to the measurement target gas introduced in
A solid electrolyte body and a pair of second electrodes formed on the solid electrolyte body, wherein one electrode of the pair of second electrodes is exposed to the second measurement chamber, and the other electrode is A second pump cell provided outside the second measurement chamber and through which a second pump current according to a specific gas concentration in the measurement target gas introduced into the second measurement chamber flows;
Have
A gas sensor element extending along the longitudinal direction so as to reach the rear end side from the front end side exposed to the measurement object gas,
The inner electrode that is the one electrode and the surrounding electrode that is the other electrode of the pair of second electrodes are both formed on the same surface of the solid electrolyte body that forms the second pump cell,
In a plan view of the same surface viewed from the vertical direction,
The peripheral electrode is disposed on a part of the outer peripheral side of the inner electrode, and is disposed in a setting region excluding a projection region obtained by projecting the inner electrode in one of the width directions perpendicular to the longitudinal direction. And
Further, the outer peripheral portion of the inner electrode includes a facing portion that faces the surrounding electrode, and of the facing portion, the maximum value of the temperature gradient in the longitudinal direction in the inner electrode when the gas sensor element is used. The gas sensor element, wherein a length of a high temperature portion existing in a high temperature region equal to or greater than a median value with a minimum value is 50% or more of a length of the facing portion. A measurement chamber into which the gas to be measured is introduced;
A reference oxygen chamber as an oxygen reference source;
A solid electrolyte body;
A pair of electrodes formed on the solid electrolyte body;
With
While one electrode of the pair of electrodes is exposed to the measurement chamber, the other electrode is exposed to the reference oxygen chamber,
A gas sensor element extending along the longitudinal direction so as to reach the rear end side from the front end side exposed to the measurement object gas,
The inner electrode which is the one electrode and the surrounding electrode which is the other electrode are both formed on the same surface of the solid electrolyte body,
In a plan view of the same surface viewed from the vertical direction,
The peripheral electrode is disposed on a part of the outer peripheral side of the inner electrode, and is disposed in a setting region excluding a projection region obtained by projecting the inner electrode in one of the width directions perpendicular to the longitudinal direction. And
Further, the outer peripheral portion of the inner electrode includes a facing portion that faces the surrounding electrode, and of the facing portion, the maximum value of the temperature gradient in the longitudinal direction in the inner electrode when the gas sensor element is used. The gas sensor element, wherein a length of a high temperature portion existing in a high temperature region equal to or greater than a median value with a minimum value is 50% or more of a length of the facing portion.   A first distance from one end of the inner electrode in the width direction to one end of the gas sensor element in the width direction is from the other end of the inner electrode in the width direction of the gas sensor element. The gas sensor element according to claim 1, wherein the gas sensor element is shorter than a second distance to the other end in the width direction.   The width direction of the surrounding electrode formed in the first region projected in the longitudinal direction from one end portion in the width direction of the inner electrode to one end portion in the width direction of the gas sensor element. The first dimension is the peripheral electrode formed in a second region projected in the longitudinal direction from the other end in the width direction of the inner electrode to the other end in the width direction of the gas sensor element. The gas sensor element according to claim 1, wherein the gas sensor element is shorter than the second dimension in the width direction.   The peripheral electrode includes a long-side peripheral electrode portion extending in the width direction on the leading end side or the rear-end side of the inner electrode, and is connected to the long-side peripheral electrode portion so as to be connected to the long-side peripheral electrode portion. 5. The gas sensor element according to claim 1, further comprising a width-side peripheral electrode portion extending in the longitudinal direction on the other side in the width direction.   The peripheral electrode includes a long side peripheral electrode portion extending in the width direction on each of the front end side and the rear end side of the inner electrode, and is connected to the both long side peripheral electrode portions. The gas sensor element according to any one of claims 1 to 4, further comprising a width-side peripheral electrode portion extending in the longitudinal direction on the other side of the width direction.   The gas sensor element according to claim 1, wherein an area of the peripheral electrode is equal to or larger than an area of the inner electrode. A gas sensor including a gas sensor element for detecting a specific gas contained in a measurement target gas,
A gas sensor comprising the gas sensor element according to claim 1 as the gas sensor element.