WO2016129661A1

WO2016129661A1 - Gas sensor

Info

Publication number: WO2016129661A1
Application number: PCT/JP2016/054082
Authority: WO
Inventors: 岳人木全; 祐介藤堂; 祐輔河本
Original assignee: 株式会社デンソー
Priority date: 2015-02-12
Filing date: 2016-02-12
Publication date: 2016-08-18

Abstract

　This gas sensor is equipped with a solid electrolyte body, a pump electrode, a sensor electrode, and a heater. In the gas sensor, the entire region R of the distal end-side portion provided with heating elements in a heater base is considered to be divided into three regions: an intermediate region R2 positioned between the distal end and the proximal end of the sensor electrode; a distal end-side region R3 positioned nearer the distal end than the intermediate region R2; and a proximal end-side region R1 positioned nearer the proximal end than the intermediate region R2. The resistance value per unit area of a heating element provided to the proximal end-side region R1 and the resistance value per unit area of a heating element provided to the distal end-side region R3 are higher than the resistance value per unit area of a heating element provided to the intermediate region R2. Thus, even if the temperature of a gas changes, the temperature near the sensor electrode will be maintained at the appropriate temperature.

Description

Gas sensor

The present invention relates to a gas sensor that detects the concentration of a predetermined gas component in a gas containing oxygen.

A gas sensor formed by laminating a plate-shaped heater on a plate-shaped solid electrolyte body has a plurality of current flows by a part of the solid electrolyte body and a pair of electrodes provided on a part of the solid electrolyte body. Has a type of cell. The plurality of cells are heated by a heater so that the electrode has an appropriate temperature having catalytic activity.

For example, the gas sensor disclosed in Patent Document 1 is provided with an electrode on a solid electrolyte layer to form a first pumping cell for controlling the oxygen partial pressure and a second pumping cell for detecting a predetermined gas component in the gas to be measured. In addition, a heater for heating the first and second pumping cells is laminated on the solid electrolyte layer. And the resistance value of the resistance part of the heater arranged so as to face the first pumping cell is made higher than the resistance value of the resistance part arranged so as to face the second pumping cell. Thereby, the temperature of the second pumping cell is lowered so that the offset current that is detected does not fluctuate even though the concentration of the predetermined gas component is zero.

JP 2009-265085 A

However, the gas sensor is held in the housing by an insulating insulator (insulator), and there is a heat sink (heat escape) from the gas sensor to the insulator. The adverse effect on the sensor due to this heat sink cannot be ignored. The adverse effect of this heat sink varies according to the variation of the gas temperature. Therefore, a technique is desired in which the temperature of each cell (electrode) in the gas sensor is less likely to fluctuate even if the gas temperature varies.

The present invention has been made in view of such problems, and has been obtained by providing a gas sensor that can maintain the temperature around the sensor electrode at an appropriate temperature even if the temperature of the gas varies. is there.

One aspect of the present invention is a plate-shaped solid electrolyte body (2) having oxygen ion conductivity,
A pump electrode (21) provided on the first surface (201) exposed to the oxygen-containing gas (G) in the solid electrolyte body and used for adjusting the oxygen concentration in the gas;
In order to detect the concentration of a predetermined gas component in the gas after the oxygen concentration is adjusted by the pump electrode provided at the position on the proximal end side of the pump electrode on the first surface of the solid electrolyte body A sensor electrode (22) used;
In a gas sensor (1) comprising: a plate-like heater (3) disposed opposite to the solid electrolyte body and heating the solid electrolyte body,
In the gas sensor, the distal end side in the longitudinal direction (L) is exposed to the gas, and the proximal end side in the longitudinal direction is held by an insulating insulator (6).
The heater is composed of a heater base (31) and a conductive conductor layer (32) provided on the heater base,
The conductor layer is connected to the pair of leads (40) disposed on the base end side and the pair of leads on the distal end side of the pair of leads, and has a cross-sectional area larger than the cross-sectional area of the leads. A small heating element (4),
In the heater base, the entire region (R) of the tip side portion (11) provided with the heating element is divided into three regions arranged in the longitudinal direction, and the three regions are divided into the sensor electrodes. An intermediate region (R2) located between the distal end (222) and the proximal end (221), a distal end side region (R3) located closer to the distal end than the intermediate region, and a proximal end side relative to the intermediate region When the base end side region (R1) is set, the resistance value per unit area of the heating element provided in the base end side region and the resistance per unit area of the heating element provided in the tip end side region The value is in the gas sensor characterized in that the value is higher than the resistance value per unit area of the heating element provided in the intermediate region.

In the above gas sensor, the method of forming the heating element of the conductor layer in the heater is devised.
Specifically, in the heater base of the heater, when the entire region of the distal end portion provided with the heating element is divided into three regions, an intermediate region, a distal end region, and a proximal end region, the proximal end The resistance value per unit area of the heating element provided in the side region is set higher than the resistance value per unit area of the heating element provided in the intermediate region. As a result, the portion of the solid electrolyte body facing the proximal end region closest to the insulating insulator among the three regions is heated more strongly than the portion of the solid electrolyte body facing the intermediate region and the periphery of the sensor electrode. Can do.

Then, by strongly heating the portion of the solid electrolyte body close to the insulating insulator, when the gas temperature is low or when the gas temperature is lowered, the sensor electrode is located on the proximal side where the insulating insulator is located. It is possible to make it less susceptible to heat sinking (heat escape).

In addition, the resistance value per unit area of the heating element provided in the tip side region is higher than the resistance value per unit area of the heating element provided in the intermediate region. Accordingly, the portion of the solid electrolyte body facing the tip region and the periphery of the pump electrode can be heated more strongly than the portion of the solid electrolyte body facing the intermediate region and the periphery of the sensor electrode. Therefore, the temperature around the pump electrode can be easily heated to an appropriate temperature having catalytic activity.
Therefore, according to the gas sensor, even if the gas temperature varies, the temperature around the sensor electrode can be maintained at an appropriate temperature. And the detection accuracy of the density | concentration of the predetermined gas component by a sensor electrode can be maintained highly.

1 is a cross-sectional view showing a gas sensor according to Example 1. FIG. The top view which shows the layout of the heat generating body in the heater base | substrate of a gas sensor concerning Example 1. FIG. The graph which shows the relationship between the distance from the front-end | tip of a gas sensor concerning Example 1, and the temperature of the gas sensor in the position. The top view which shows the layout of the heat generating body in the heater base | substrate of a gas sensor concerning Example 3. FIG. The top view which shows the layout of the heat generating body in the heater base | substrate of the other gas sensor concerning Example 3. FIG. The top view which shows the layout of the heat generating body in the heater base | substrate of the other gas sensor concerning Example 3. FIG. The top view which shows the layout of the heat generating body in the heater base | substrate of the other gas sensor concerning Example 3. FIG. The top view which shows the layout of the heat generating body in the heater base | substrate of the other gas sensor concerning Example 3. FIG. The top view which shows the layout of the heat generating body in the heater base | substrate of a gas sensor concerning a comparative example.

A preferred embodiment of the gas sensor described above will be described.
In the present disclosure, the “resistance value per unit area” means a value obtained by dividing the resistance value of the heating element in each of a plurality of predetermined regions of the gas sensor by the area of the region. “Resistance value” means a value obtained by measuring the current flowing through a heating element provided in each region when a predetermined voltage is applied and dividing the predetermined voltage by the measured current. Say.

In addition, the “intermediate region” refers to a region on the heater base that exists between the tip of the sensor electrode and the base end facing the tip. The “front end side region” indicates the entire region on the front side of the heater base further than the front end of the sensor electrode in the heater base. The “proximal end region” refers to the entire region of the heater base that is located further to the base end side of the heater base than the base end of the sensor electrode in the tip side portion where the heating element is provided. Further, the tip side portion of the heater base where the heating element is provided indicates the entire region of the heater base located on the tip side of the end where the heating element is connected to the lead.

In addition, the entire heating element has a constant cross-sectional area along the width direction of the heating element, the length per unit area of the heating element provided in the proximal end region, and the distal end side The length per unit area of the heating element provided in the region can be longer than the length per unit area of the heating element provided in the intermediate region.

Thereby, the resistance value per unit area of the heating element provided in the base end region is higher than the resistance value per unit area of the heating element provided in the intermediate region by forming the heating element long. can do. Also, the resistance value per unit area of the heating element provided in the tip side region should be higher than the resistance value per unit area of the heating element provided in the intermediate region by forming the heating element long. Can do.
The “length per unit area” refers to a value obtained by dividing the total length of the heating element provided in each region by the area of each region.

Further, the average value of the cross-sectional area per unit length of the heating element provided in the base end side region, and the average value of the cross-sectional area per unit length of the heating element provided in the distal end side region are: The average value of the cross-sectional area per unit length of the heating element provided in the intermediate region can be reduced.

Thereby, the resistance value per unit area of the heating element provided in the base end region is smaller than the resistance value per unit area of the heating element provided in the intermediate region by reducing the cross-sectional area of the heating element. Can also be high. In addition, the resistance value per unit area of the heating element provided in the tip side region is higher than the resistance value per unit area of the heating element provided in the intermediate region by reducing the cross-sectional area of the heating element. can do.
The “average value of the cross-sectional area per unit area” means a value obtained by dividing the average value of the cross-sectional areas in the width direction of the heating elements provided in each region by the area of each region. Further, the “heating element having a constant cross-sectional area” may include a change in cross-sectional area within ± 10%.

Hereinafter, the gas sensor according to the present embodiment will be described with reference to the drawings.
(Example 1)
As shown in FIGS. 1 and 2, the gas sensor 1 includes a solid electrolyte body 2, a pump electrode 21, a sensor electrode 22, and a heater 3.

The solid electrolyte body 2 has oxygen ion conductivity and is formed in a plate shape. The pump electrode 21 is provided on the first surface 201 of the solid electrolyte body 2 exposed to the gas G containing oxygen, and is used to adjust the oxygen concentration in the gas G. The sensor electrode 22 is provided on the first surface 201 of the solid electrolyte body 2 on the proximal end side of the solid electrolyte body 2 with respect to the pump electrode 21. The sensor electrode 22 is used for detecting the concentration of a predetermined gas component in the gas G after the oxygen concentration is adjusted by the pump electrode 21. The heater 3 is formed in a plate shape and faces the solid electrolyte body 2, and heats the solid electrolyte body 2 and the

electrodes

21 and 22.

The gas sensor 1 has a predetermined length and has two end portions facing each other in the longitudinal direction (longitudinal direction). In this disclosure, one of the two ends exposed to the gas G is referred to as a distal end side, and the other held by the insulator 6 is referred to as a proximal end side. As described above, the gas sensor 1 is formed in a long shape, and the “tip side” is also a free end of the gas sensor 1. On the other hand, the “base end side” of the gas sensor 1 is opposed to the distal end side in the longitudinal direction L of the gas sensor 1 and is held by the insulator 6 as described above.

As shown in FIGS. 1 and 2, the heater 3 includes an insulating heater base 31 and a conductive conductor layer 32 provided on the heater base 31. The conductor layer 32 is closer to the distal end side than the pair of leads 40 arranged on the base end side, connects the pair of leads 40 to each other, and generates heat in a cross-sectional area smaller than the cross-sectional area of the lead 40. It has a body 4.

As shown in FIG. 2, the heater base 31 of the gas sensor 1 has a portion close to the distal end side of the gas sensor 1 and provided with a heating element 4. In the following description, this portion is referred to as the tip end portion 11. The entire region of the tip end portion 11 is defined as region R, which is divided into three regions R1, R2, and R3 arranged in the longitudinal direction L as shown in the figure. The region R2 is located between the distal end 222 and the proximal end 221 of the sensor electrode 22, and is hereinafter referred to as an intermediate region R2. The region R3 is closer to the tip side than the intermediate region R2, and is referred to as a tip side region R3. The region R1 is closer to the base end side than the intermediate region R2, and is referred to as a base end region R1. By changing the pattern of the heating element 4, that is, the layout, the resistance value per unit area of the heating element 41 provided in the base end region R1 and the per unit area of the heating element 43 provided in the tip end region R3. Is set to be higher than the resistance value per unit area of the heating element 42 provided in the intermediate region R2. That is, the heating element 4 has three

portions

41, 42, and 43. The portion 41 is located in the region R1, the portion 42 is located in the region R2, and the portion 43 is located in the region R30. The “resistance value per unit area” is represented by a value obtained by dividing the resistance values of the

heating elements

41, 42, and 43 provided in the regions R1, R2, and R3 by the areas of the regions R1, R2, and R3. .
Here, the tip end portion 11 of the heater base 31 provided with the heating element 4 is the region of the heater base 31 closer to the tip end side than the end 401 where the heating element 4 is connected to the lead 40. Show the whole thing.

Hereinafter, the gas sensor 1 will be described in detail with reference to FIGS.
The gas sensor 1 is disposed and used in an exhaust pipe or the like of an internal combustion engine. The gas G contains oxygen and is exhaust gas that passes through an exhaust pipe extending from the internal combustion engine, and the predetermined gas component is NOx (nitrogen oxide) contained in the exhaust gas. The gas sensor 1 is held in the housing by the insulator 6, and the housing is fixed to the exhaust pipe. Further, the gas sensor 1 has a tip portion protruding from the insulator 6, and the tip portion is covered with a protective cover provided with a through hole through which the gas G passes.

As shown in FIG. 1, the solid electrolyte body 2 has a first surface 201 and a second surface 202 that face each other in the thickness direction of the solid electrolyte body 2. A reference electrode 24 is provided on the second surface 202 exposed to the atmosphere as the reference gas A. The reference electrode 24 matches the pump electrode 21 and the sensor electrode 22 provided on the first surface 201 of the solid electrolyte body 2 in the thickness direction of the solid electrolyte body 2, in other words, the second electrode that overlaps. A part of the surface 202 is provided. The reference electrode 24 includes a single electrode and can be configured to have a size that completely overlaps the pump electrode 21 and the sensor electrode 22. Further, the reference electrode 24 may be constituted by a combination of a plurality of independent electrodes, or one reference electrode 24 may be provided for each of the pump electrode 21 and the sensor electrode 22.

The pump electrode 21, the sensor electrode 22 and the reference electrode 24 are provided for one solid electrolyte body 2. A plate-like insulator 52 is stacked on the first surface 201 of the solid electrolyte body 2 with a spacer 51 interposed therebetween. On the first surface 201 side of the solid electrolyte body 2, a gas chamber 501 into which the gas G is introduced is formed by the solid electrolyte body 2, the spacer 51, and the insulator 52. A diffusion resistance layer 511 for introducing the gas G into the gas chamber 501 under a predetermined diffusion resistance is provided in the hole provided in the spacer 51. The heater 3 is stacked on the second surface 202 of the solid electrolyte body 2 with a spacer 53 interposed therebetween. On the second surface 202 side of the solid electrolyte body 2, a reference gas chamber 502 into which the reference gas A is introduced is formed by the solid electrolyte body 2, the spacer 53, and the heater 3.

The pump electrode 21 and the reference electrode 24 are made of a material having catalytic activity for oxygen such as platinum and gold. The sensor electrode 22 is made of a material obtained by adding rhodium or the like having catalytic activity for NOx to platinum.

In the gas sensor 1, a pump cell is formed by the pump electrode 21 and the reference electrode 24 (a part of the reference electrode 24 in this example) and a part of the solid electrolyte body 2 sandwiched therebetween. The pump cell is configured to remove oxygen in the gas G by applying a voltage between the pump electrode 21 and the reference electrode 24 and causing an oxygen ion current to flow between the pump electrode 21 and the reference electrode 24. ing.

Further, in the gas sensor 1, a sensor cell is formed by the sensor electrode 22 and the reference electrode 24 (in this example, a part of the reference electrode 24) and a part of the solid electrolyte body 2 sandwiched therebetween. . The sensor cell is configured to detect an oxygen ion current flowing between the sensor electrode 22 and the reference electrode 24 in a state where a voltage is applied between the sensor electrode 22 and the reference electrode 24. Then, the NOx concentration in the gas G is calculated as a function of the level of this oxygen ion current.

The heater base 31, the insulator 52, and the

spacers

51 and 53 are made of ceramics such as alumina. The conductor layer 32 is made of a conductive material provided on the heater base 31 with a constant thickness. The conductor layer 32 is formed so as to be sandwiched between a pair of heater bases 31. The pair of leads 40 in the conductor layer 32 extend in parallel to each other at the proximal end portion of the heater base 31. The heating element 4 in the conductor layer 32 generates a Joule heat larger than that of the leads 40 when energizing between the pair of leads 40 due to the reduced cross-sectional area compared to the leads 40.

As shown in FIG. 2, the heating element 4 has a certain width over its entire length. Furthermore, the heating element 4 has a constant cross-sectional area over its entire length. The formation pattern, that is, the layout of the heating element 4 changes in the base end region R1, the intermediate region R2, and the distal end region R3. The length per unit area of the

heating elements

41, 42, and 43 provided in each of the regions R1, R2, and R3 is made different depending on the layout of the heating element 4. Here, the “length per unit area” is a value obtained by dividing the total length of the

heating elements

41, 42, 43 provided in the regions R1, R2, R3 by the areas of the regions R1, R2, R3. expressed.

That is, the length per unit area of the heating element 41 provided in the base end region R1 and the length per unit area of the heating element 43 provided in the tip end region R3 are provided in the intermediate region R2. It is larger than the length per unit area of the heating element 42. Further, the length per unit area of the heating element 41 provided in the base end side region R1 is larger than the length per unit area of the heating element 43 provided in the distal end side region R3.

The heating element 41 in the proximal end region R1 meanders in the width direction W by a portion parallel to the longitudinal direction L of the heater 3 and a portion parallel to the width direction W orthogonal to the longitudinal direction L. The heating element 41 in the base end side region R1 is configured by two conductors extending symmetrically in the width direction W. The heating element 42 in the intermediate region R2 is composed of two conductors parallel to the longitudinal direction L and symmetrical in the width direction W. The two conductors of the heating element 42 located in the intermediate region R2 are a part of the intermediate region R2 and coincide with the sensor electrode 22 in the thickness direction of the heater base 31, that is, both regions in the width direction W of the overlapping region. Located on the outside. The heating element 43 in the distal end side region R3 meanders in the longitudinal direction L by a portion parallel to the longitudinal direction L and a portion parallel to the width direction W. In other words, the heating element 43 in the distal end side region R3 is composed of two conductors symmetrical in the width direction W. That is, the heating element 43 in the distal end side region R3 is composed of two outer portions 431 extending in parallel to the longitudinal direction L and two inner portions 432 extending in parallel to the longitudinal direction L, and each is connected at the distal end side. The inner portions 432 are connected to each other on the proximal end side.

In the gas sensor 1, as described above, the entire region R of the distal end portion 11 provided with the heating element 4 of the heater base 31 is divided into three regions arranged in the longitudinal direction L of the gas sensor 1. The heat generation characteristics (heat generation amount) of the heating element 4 in the region are different. The three regions are a distal end region R3 facing the pump electrode 21, an intermediate region R2 positioned between the distal end 222 and the proximal end 221 of the sensor electrode 22, and a proximal end side positioned closer to the proximal end than the sensor electrode 22 Region R1.

Then, the resistance value per unit area of the heating element 41 provided in the proximal end region R1 and the resistance value per unit area of the heating element 43 provided in the distal end region R3 are provided in the intermediate region R2. By making it higher than the resistance value per unit area of the heating element 42, the heating amount in the base end side region R1 and the distal end side region R3 is made larger than the heating amount in the intermediate region R2.

As described above, of the three regions, the portion of the solid electrolyte body 2 facing the proximal end region R1 closest to the insulator 6 in the thickness direction of the heater base 31 is changed to the portion of the solid electrolyte body 2 facing the intermediate region R2. And it can heat more strongly than the periphery of the sensor electrode 22. Moreover, the part of the solid electrolyte body 2 which opposes the periphery of the pump electrode 21 and the part of the solid electrolyte body 2 which opposes front-end | tip side area | region R3 located in the front end side of the elongate direction L among three area | regions. And it can heat more strongly than the periphery of the sensor electrode 22.

It should be noted that either the resistance value per unit area of the heating element 41 provided in the base end region R1 or the resistance value per unit area of the heating element 43 provided in the distal end region R3 may be increased. Is possible.

In the distal end side region R3, the influence of heat sinking (heat escape) toward the proximal end where the insulator 6 is located is small, and the periphery of the pump electrode 21 corresponding to the distal end side region R3 is in the longitudinal direction L of the gas sensor 1. It becomes the highest temperature. Moreover, in the base end side area | region R1, the influence of the heat sink to the base end side in which the insulator 6 is located is large. Therefore, in the gas sensor 1, the resistance value per unit area of the heating element 41 provided in the proximal end region R1 is set higher than the resistance value per unit area of the heating element 43 provided in the distal end region R3. Thus, the portion of the solid electrolyte body 2 facing the base end region R1 is heated more strongly. Thus, the periphery of the sensor electrode 22 corresponding to the intermediate region R2 and the portion on the base end side of the sensor electrode 22 are maintained at an appropriate temperature lower than the temperature of the periphery of the pump electrode 21. Further, the temperature around the pump electrode 21 is maintained at an appropriate temperature having catalytic activity.

Generally, the temperature of the gas (exhaust gas) G exhausted from the internal combustion engine is often lower than the target temperature at which the solid electrolyte body 2 is heated by the heater 3. In the case of lean combustion of the internal combustion engine, the temperature of the gas (exhaust gas) G may be significantly lower than the target temperature for heating the solid electrolyte body 2. At this time, heat sink (heat escape) from the gas sensor 1 toward the base end where the insulator 6 is located becomes a problem.

Further, the temperature of the gas (exhaust gas) G flowing through the exhaust pipe of the internal combustion engine in which the gas sensor 1 is disposed is repeatedly increased and decreased under the influence of the combustion cycle of the internal combustion engine. And when the temperature of gas G falls, the heat | fever contraction (heat escape) from the gas sensor 1 to the base end side in which the insulator 6 is located becomes a problem.

Therefore, in the gas sensor 1, even when the temperature of the gas G is lowered by strongly heating the portion of the solid electrolyte body 2 close to the insulator 6, the sensor electrode 22 is heated to the proximal side where the insulator 6 is located. It can be made less susceptible to shrinkage (heat escape).
Therefore, according to the gas sensor 1, even if the temperature of the gas G varies, the temperature around the sensor electrode 22 is maintained at an appropriate temperature. And the detection accuracy of the density | concentration of the predetermined gas component by the sensor electrode 22 is maintained highly.

FIG. 3 shows the relationship between the distance (mm) from the tip of the gas sensor 1 and the temperature (° C.) of the portion at the distance from the tip of the gas sensor 1 for comparison with the gas sensor 1 (FIG. 2). A conventional gas sensor 9 (FIG. 9) will be described. As shown in FIG. 9, the heating element 94 of the heater 93 of the conventional gas sensor 9 is not provided with the heating element 41 in the proximal end region R <b> 1 of the heater base 31. The graph of FIG. 3 shows the result of simulation for the temperature of the gas sensors 1 and 9.

Here, in FIG. 3, for the gas sensor 1, the temperature change of the gas sensor 1 when the temperature of the gas G is 500 ° C. is indicated by a symbol E 1, and the temperature change of the gas sensor 1 when the temperature of the gas G is 200 ° C. It shows with. Further, in the same figure, for the conventional gas sensor 9, the temperature change of the gas sensor 9 when the temperature of the gas G is 500 ° C. is denoted by reference numeral F1, and the temperature change of the gas sensor 9 when the temperature of the gas G is 200 ° C. is denoted by This is indicated by F2.

In both the gas sensor 1 of this example and the conventional gas sensor 9, there is a temperature peak near the center of the pump electrode 21 (pump cell) in the longitudinal direction L. The temperature near the sensor electrode 22 (sensor cell) is lower than the temperature near the pump electrode 21.
In the conventional gas sensor 9, when the temperature of the gas G is decreased from 500 ° C. to 200 ° C., the temperature in the vicinity of the sensor electrode 22 is significantly decreased. The temperature drop in the vicinity of the sensor electrode 22 is caused by being affected by heat sinking toward the base end side of the gas sensor 9.

On the other hand, in the gas sensor 1 of this example, even if the temperature of the gas G is decreased from 500 ° C. to 200 ° C., the temperature near the sensor electrode 22 hardly changes. The effect of suppressing the temperature change in the vicinity of the sensor electrode 22 is that the portion of the solid electrolyte body 2 facing the proximal end region R1 closest to the insulator 6 is replaced with the portion of the solid electrolyte body 2 facing the intermediate region R2 and the sensor electrode. It is obtained by heating more strongly than the vicinity of 22. That is, the gas sensor 1 can maintain the temperature around the sensor electrode 22 at an appropriate temperature even if the temperature of the gas G varies.
Further, in the gas sensor 1, when a monitor electrode 23 (monitor cell) described later is formed (Example 2), the temperature of the monitor electrode 23 is equal to the temperature of the sensor electrode 22.

(Example 2)
In this example, a sensor electrode 22 and a monitor electrode 23 arranged in the width direction W of the solid electrolyte body 2 are provided on the first surface 201 of the solid electrolyte body 2 at a position closer to the base end side than the pump electrode 21. (See FIG. 1).

The monitor electrode 23 is used for detecting the oxygen concentration in the gas G after the oxygen concentration is adjusted by the pump electrode 21. The distance from the center of the pump electrode 21 to the center of the sensor electrode 22 and the distance from the center of the pump electrode 21 to the center of the monitor electrode 23 are substantially equal.

The monitor electrode 23 is made of a material having catalytic activity for oxygen such as platinum or gold. The reference electrode 24 is provided on the second surface 202 of the solid electrolyte body 2 and faces the monitor electrode 23 in the thickness direction of the solid electrolyte body 2. In the gas sensor 1, a monitor cell is formed by the monitor electrode 23 and the reference electrode 24 (in this example, a part of the reference electrode 24) and a part of the solid electrolyte body 2 sandwiched therebetween. The monitor cell is configured to detect an oxygen ion current flowing between the monitor electrode 23 and the reference electrode 24 in a state where a voltage is applied between the monitor electrode 23 and the reference electrode 24.

The sensor cell generates an oxygen ion current caused by NOx and residual oxygen, while the monitor cell generates an oxygen ion current caused by residual oxygen. Then, the NOx concentration in the gas G is detected by subtracting the value of the oxygen ion current in the monitor cell from the value of the oxygen ion current in the sensor cell.

The pump electrode 21, sensor electrode 22, monitor electrode 23, and reference electrode 24 are formed by a single solid electrolyte body 2.
Other configurations of the gas sensor 1 of this example and the reference numerals in the figure are the same as those of the first embodiment, and the same effects as those of the first embodiment are obtained.

(Example 3)
In this example, the layout of the heating element 4 in the heater base 31 is different from that in the first embodiment.
As shown in FIG. 4, the central portion 415 of the heating element 41 in the base region R1 can be formed in a state connected to the inner portion 422 of the heating element 42 in the intermediate region R2. In this case, the volume of the heating element 42 present in the intermediate region R2 is larger than that in the case of the first embodiment (FIG.), And the periphery of the sensor electrode 22 can be strongly heated as compared with the case of the first embodiment. .

Further, as shown in FIG. 5, the heating element 43 in the distal end side region R3 includes a portion parallel to the longitudinal direction L and a portion parallel to the width direction W, similarly to the heating element 41 in the proximal end region R1. These are continuous and can be formed to meander in the width direction W. The heating elements 42 in the intermediate region R2 are provided on both sides (outside) in the width direction W of the region facing the sensor electrode 22 in the thickness direction of the solid electrolyte body 2. In this case, as shown in FIG. 6, the heating element 41 in the proximal end region R <b> 1 meanders in the longitudinal direction L by a portion parallel to the longitudinal direction L and a portion parallel to the width direction W. It can also be formed.

Further, as shown in FIGS. 7 and 8, the width of at least a part of the heating element 42 in the intermediate region R2 is set to be larger than the width of the heating element 4 in the proximal end region R1 and the width of the heating element 4 in the distal end region R3. May be larger. In this case, the heating element 4 includes an outer portion 411 and an inner portion 412 provided in a pair in parallel to the longitudinal direction L in the entire base end region R1, intermediate region R2, and tip end region R3. And meandering in the longitudinal direction L. And as shown in FIG. 7, the width | variety of a pair of outer side part 411 in intermediate | middle area | region R2 can be enlarged compared with the width | variety of the other part of the heat generating body 4. FIG. Further, as shown in FIG. 8, the width of the pair of inner portions 412 in the intermediate region R <b> 2 can be made larger than the width of other portions of the heating element 4.

In the case of FIGS. 7 and 8, the average value of the cross-sectional area per unit length of the heating element 41 provided in the proximal end region R1 and the unit length of the heating element 43 provided in the distal end region R3. The average value of the hit area is smaller than the average value of the cross-sectional area per unit length of the heating element 42 provided in the intermediate region R2. Here, “the average value of the cross-sectional area per unit area” means the average value of the cross-sectional areas of the

heating elements

41, 42, 43 provided in the regions R1, R2, R3, and the regions R1, R2, R3. It is represented by the value divided by the area.

As a result, the resistance value per unit area of the heating element 41 in the proximal end region R1 and the resistance value per unit area of the heating element 43 in the distal end region R3 are the same as the resistance value per unit area of the heating element 42 in the intermediate region R2. It becomes higher than the resistance value. And the heating amount in the base end side region R1 and the leading end side region R3 can be made larger than the heating amount in the intermediate region R2.
Also in the gas sensor 1 of this example, the other configurations and the reference numerals in the figure are the same as those in the first embodiment, and the same effects as those in the first embodiment can be obtained.

Claims

A plate-like solid electrolyte body (2) having oxygen ion conductivity;
A pump electrode (21) provided on the first surface (201) exposed to the oxygen-containing gas (G) in the solid electrolyte body and used for adjusting the oxygen concentration in the gas;
In order to detect the concentration of a predetermined gas component in the gas after the oxygen concentration is adjusted by the pump electrode provided at the position on the proximal end side of the pump electrode on the first surface of the solid electrolyte body A sensor electrode (22) used;
In a gas sensor (1) comprising: a plate-like heater (3) disposed opposite to the solid electrolyte body and heating the solid electrolyte body,
In the gas sensor, the distal end side in the longitudinal direction (L) is exposed to the gas, and the proximal end side in the longitudinal direction is held by an insulating insulator (6).
The heater is composed of a heater base (31) and a conductive conductor layer (32) provided on the heater base,
The conductor layer is connected to the pair of leads (40) disposed on the base end side and the pair of leads on the distal end side of the pair of leads, and has a cross-sectional area larger than the cross-sectional area of the leads. A small heating element (4),
In the heater base, the entire region (R) of the tip side portion (11) provided with the heating element is divided into three regions arranged in the longitudinal direction, and the three regions are divided into the sensor electrodes. An intermediate region (R2) located between the distal end (222) and the proximal end (221), a distal end side region (R3) located closer to the distal end than the intermediate region, and a proximal end side relative to the intermediate region When the base end side region (R1) is set, the resistance value per unit area of the heating element provided in the base end side region and the resistance per unit area of the heating element provided in the tip end side region A gas sensor characterized in that a value is higher than a resistance value per unit area of the heating element provided in the intermediate region.
The entire heating element is formed with a constant cross-sectional area,
The length per unit area of the heating element provided in the proximal end region and the length per unit area of the heating element provided in the distal end region are the heat generation provided in the intermediate region. The gas sensor according to claim 1, wherein the gas sensor is longer than a length per unit area of the body.
The average value of the cross-sectional area per unit length of the heating element provided in the base end side region and the average value of the cross-sectional area per unit length of the heating element provided in the distal end side region are The gas sensor according to claim 1 or 2, wherein the gas sensor is smaller than an average value of a cross-sectional area per unit length of the heating element provided in the intermediate region.