JP2015230178A - Gas sensor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor element capable of suppressing the generation of a temperature distribution in a measurement target gas space and improving detection accuracy.SOLUTION: A gas sensor element 1 comprises: a solid electrolyte element 2 having oxygen ion conductivity; an insulator 4 stacked on a first surface 201 of the solid electrolyte element 2 and forming a measurement target gas space 61; and a heater 5 stacked on a second surface 202 of the solid electrolyte element 2 and heating the solid electrolyte element 2. In a stacking direction D of a tip end portion 11 of the gas sensor element 1 in which electrodes 21, 22, 23, and 25 are provided on the solid electrolyte element 2, a thickness T1 from the first surface 201 to an outer side surface 501 of the heater 5 and a thickness T2 from the first surface 201 to an outer side surface 401 of the insulator 4 have a relation of 0.7≤T2/T1≤1.6.

Description

  The present invention relates to a gas sensor element that measures an oxygen ion current.

  A laminated gas sensor element is a heater in which an insulator forming a gas space to be measured is laminated on one side of a solid electrolyte body provided with electrodes on both sides, and the solid electrolyte body is heated on the other side of the solid electrolyte body. Are laminated. In the gas sensor element, the solid electrolyte body and the electrode are heated by a heater, and the solid electrolyte body and the electrode are brought to a temperature having oxygen decomposition activity. Then, the oxygen ion current flowing between the electrodes is measured to detect the oxygen concentration or the specific gas concentration in the gas to be measured.

  For example, the laminated gas sensor element of Patent Document 1 has a wide width portion fixed to an insulator and a width detail in a free state. The width detail is formed at a tip portion protruding from the insulator, and a gas detector for detecting a specific gas concentration in the gas to be measured is formed at the tip portion. In Patent Document 1, a laminated gas sensor element that is strong against impact and hardly damages is formed by providing a wide portion and a wide detail.

JP 2004-3963 A

  By the way, when the solid electrolyte body is heated by the heater, heat is lost from the outer surface of the insulator laminated on the side opposite to the side on which the heater is laminated with respect to the solid electrolyte body. And when the thickness of the insulator laminated on the solid electrolyte body is thin, the heat lost from the outer surface of the insulator becomes remarkable, and the temperature distribution is likely to occur in the measured gas space. When this temperature distribution occurs, an error occurs in the measured oxygen ion current, which causes a decrease in detection accuracy by the gas sensor element.

  The present invention has been made in view of such a background, and has been obtained in an attempt to provide a gas sensor element that makes it difficult for temperature distribution to occur in a gas space to be measured and improves detection accuracy.

One aspect of the present invention is a solid electrolyte body having oxygen ion conductivity and having electrodes provided on a first surface as one surface and a second surface as the other surface;
An insulator that is laminated on the first surface side of the solid electrolyte body, and that forms a measurement gas space into which the measurement gas is introduced through the diffusion resistor;
A gas sensor element comprising: a heater laminated on the second surface side of the solid electrolyte body and heating the solid electrolyte body,
A thickness T1 from the first surface to the outer surface of the heater in the stacking direction of the tip side portion of the gas sensor element where the electrode is provided on the solid electrolyte body, and the outside of the insulator from the first surface. The thickness T2 up to the side surface is a gas sensor element having a relation of 0.7 ≦ T2 / T1 ≦ 1.6.

The gas sensor element is formed by laminating an insulator and a heater on both surface sides of a solid electrolyte body. And in the front end side part of a gas sensor element, the thickness of the lamination direction of an insulator and the thickness of the lamination direction of a heater are devised.
Specifically, in the stacking direction of the tip side portion of the gas sensor element, a thickness T1 from the first surface of the solid electrolyte body to the outer surface of the heater, and a thickness T2 from the first surface to the outer surface of the insulator are: The relationship is 0.7 ≦ T2 / T1 ≦ 1.6.

Thereby, the thickness T2 on the insulator side is appropriately increased. And when a solid electrolyte body is heated with a heater, the heat which escapes from the outer surface of an insulator can be reduced. As a result, the gas to be measured in the gas space to be measured is hardly cooled, and the temperature distribution can be hardly generated in the gas space to be measured.
Thereby, it becomes difficult to produce an error in the oxygen ion current measured by flowing between the electrodes in the solid electrolyte body, and the detection accuracy by the gas sensor element can be improved.

  According to the gas sensor element, a temperature distribution is hardly generated in the gas space to be measured, and detection accuracy can be improved.

Cross-sectional explanatory drawing which shows the gas sensor element concerning an Example. Cross-sectional explanatory drawing which shows the front end side part of the gas sensor element concerning an Example. It is a figure which shows the front end side part of the gas sensor element concerning an Example, and is II arrow directional cross-section explanatory drawing of FIG. Cross-sectional explanatory drawing which shows the front end side part of the other gas sensor element concerning an Example. Cross-sectional explanatory drawing which shows the front end side part of the other gas sensor element concerning an Example.

A preferred embodiment of the gas sensor element described above will be described.
In the gas sensor element, when 0.7> T2 / T1, the thickness T2 from the first surface to the outer surface of the insulator is small, and heat is easily lost from the outer surface of the insulator, so that the gas to be measured Temperature distribution tends to occur in the space. On the other hand, in the case of T2 / T1> 1.6, the thickness T2 from the first surface to the outer surface of the insulator is large, and it is difficult to lose heat from the outer surface of the insulator, so that the gas space to be measured The temperature distribution tends to occur inside.

Moreover, the thickness in the stacking direction of the insulator in the front end portion of the gas sensor element may be larger than the thickness in the stacking direction of the insulator in the rear end portion of the gas sensor element.
In this case, the gas sensor element having a relation of 0.7 ≦ T2 / T1 ≦ 1.6 can be increased only in the thickness of the insulator in the stacking direction only at the tip side portion where the electrode is provided on the solid electrolyte body. Can be easily formed.

Moreover, the said insulator in the front end side part of the said gas sensor element may be laminated | stacked by the said lamination direction, and the lamination | stacking interface may be formed between these insulators.
In this case, the heat conduction in the stacking direction of the insulator can be weakened by the stacking interface. Further, the heat of the gas to be measured in the solid electrolyte body and the gas space to be measured heated by the heater can be made difficult to escape to the outer surface of the insulator by the laminated interface.

In addition, a low thermal conductor made of a material having a lower thermal conductivity than the insulator may be laminated on the insulator in the tip side portion of the gas sensor element.
In this case, the heat conduction in the stacking direction of the insulator can be weakened by the low heat conductor. The heat of the gas to be measured in the solid electrolyte body and the gas space to be measured heated by the heater can be made difficult to escape to the outer surface of the insulator by the low thermal conductor.
The insulator can be made of a ceramic material such as alumina. The low thermal conductor can be composed of silicon nitride, titanium nitride, titanium carbide, yttria, mullite, forsterite, sialon, cordierite, zirconia, steatite, silicon dioxide, or the like.

Below, the example concerning a gas sensor element is described with reference to drawings.
As shown in FIGS. 1 to 3, the gas sensor element 1 of this example includes a solid electrolyte body 2, an insulator 4, and a heater 5. The solid electrolyte body 2 has oxygen ion conductivity, and has electrodes 21, 22, 23, and 25 on a first surface 201 as one surface and a second surface 202 as the other surface. . The insulator 4 is laminated on the first surface 201 side of the solid electrolyte body 2, and forms a measured gas space 61 into which the measured gas G is introduced through the diffusion resistor 43. The heater 5 is laminated on the second surface 202 side of the solid electrolyte body 2 and is configured to heat the solid electrolyte body 2. A reference gas space 62 into which the reference gas A is introduced is formed between the second surface 202 of the solid electrolyte body 2 and the heater 5.
A thickness T1 from the first surface 201 to the outer surface 501 of the heater 5 in the stacking direction D of the tip end portion 11 of the gas sensor element 1 where the electrodes 21, 22, 23, and 25 are provided on the solid electrolyte body 2; The thickness T2 from one surface 201 to the outer side surface 401 of the insulator 4 has a relationship of 0.7 ≦ T2 / T1 ≦ 1.6.

Hereinafter, the gas sensor element 1 of this example will be described in detail with reference to FIGS.
The gas sensor element 1 of this example constitutes a gas sensor while being held by an insulator and housed in a cover. The gas sensor element 1 has an elongated shape, and the tip side including the tip side portion 11 protrudes from the insulator and is exposed to the gas G to be measured.
A gas sensor is disposed and used in an exhaust pipe of a vehicle. The gas G to be measured is exhaust gas that passes through the exhaust pipe, and the gas sensor is used to detect the concentration of NOx (nitrogen oxide) as a specific gas in the exhaust gas. The gas sensor can also detect A / F (air-fuel ratio) from the oxygen concentration in the gas G to be measured.

  As shown in FIG. 2, the diffusion resistor 43 is provided at the distal end portion in the longitudinal direction L of the gas sensor element 1. The diffusion resistor 43 is provided between the solid electrolyte body 2 and the insulator 4 adjacent to the first surface 201 of the solid electrolyte body 2. The gas space 61 to be measured is the front end portion 11 of the gas sensor element 1 and is formed adjacent to the rear end side in the longitudinal direction L with respect to the diffusion resistor 43. The diffusion resistor 43 is made of a porous material having a gas-permeating property so that the measurement gas G is introduced into the measurement gas space 61 at a predetermined diffusion rate. The flow direction F of the gas G to be measured in the gas sensor element 1 is a direction from one side of the longitudinal direction L toward the other side.

  As shown in FIGS. 2 and 3, the solid electrolyte body 2 is composed of a zirconia substrate having oxygen ion conductivity. The solid electrolyte body 2 is provided with a pump cell 31, a monitor cell 32, and a sensor cell 33. The pump cell 31 applies a voltage between the electrode 21 provided on the first surface 201 of the solid electrolyte body 2 and the electrode 25 provided on the second surface 202 to reduce the oxygen concentration in the measured gas space 61. Configured to adjust.

  The monitor cell 32 measures the oxygen ion current that flows between the electrode 22 provided on the first surface 201 of the solid electrolyte body 2 and the electrode 25 provided on the second surface 202, and thereby in the measured gas space 61. The residual oxygen concentration after the oxygen concentration is adjusted by the pump cell 31 is measured. The sensor cell 33 measures an oxygen ion current flowing between the electrode 23 provided on the first surface 201 of the solid electrolyte body 2 and the electrode 25 provided on the second surface 202, and thereby in the measured gas space 61. The specific gas concentration in the gas G to be measured after the oxygen concentration is adjusted by the pump cell 31 is measured. The specific gas concentration in the measurement gas G is detected based on the difference between the oxygen ion current in the sensor cell 33 and the oxygen ion current in the monitor cell 32.

  Each electrode 21, 22, 23, 25 constituting the pump cell 31, the monitor cell 32 and the sensor cell 33 is provided for one solid electrolyte body 2. The electrodes 22 and 23 constituting the monitor cell 32 and the sensor cell 33 are provided adjacent to the rear end side in the longitudinal direction L with respect to the electrode 21 constituting the pump cell 31. The pump cell 31 has voltage application means for applying a voltage between the pair of electrodes 21 and 25. The monitor cell 32 has a current measuring means for measuring the current flowing between the pair of electrodes 22 and 25. The sensor cell 33 has current measuring means for measuring a current flowing between the pair of electrodes 23 and 25.

  As shown in FIGS. 2 and 3, the insulator 4 is made of an insulating material such as alumina. The insulator 4 is laminated on the first surface 201 of the solid electrolyte body 2 with a first spacer 41 made of an insulating material such as alumina interposed therebetween. The gas space 61 to be measured on the first surface 201 of the solid electrolyte body 2 is surrounded by the insulator 4 and the first spacer 41.

  The heater 5 is configured by disposing a heating element 52 that generates heat when energized in a ceramic substrate 51 made of an insulating material such as alumina. The heating element 52 is formed to meander at a position overlapping the measurement gas space 61 in the stacking direction D. The heater 5 is stacked on the second surface 202 of the solid electrolyte body 2 with a second spacer 42 made of an insulating material such as alumina interposed therebetween. The reference gas space 62 on the second surface 202 of the solid electrolyte body 2 is formed surrounded by the heater 5 and the second spacer 42.

  As shown in FIG. 1, the gas sensor element 1 has a thickness T3 in the stacking direction D of the insulator 4 at the front end portion 11 larger than a thickness T4 in the stacking direction D of the insulator 4 at the rear end portion 12. Is formed. Further, a step 44 due to a difference in thickness is formed between the front end side portion 11 and the rear end side portion 12 of the gas sensor element 1. The ratio T2 / T1 of the thickness in the distal end portion 11 of the gas sensor element 1 satisfies the relationship of 0.7 ≦ T2 / T1 ≦ 1.6 by increasing the thickness.

  Although not shown, the tip portion 11 of the gas sensor element 1 is provided with a trap layer for trapping poisonous substances in the measurement gas in order to suppress poisoning of the electrodes 21, 22, and 23. Yes. Since the trap layer has a high porosity of 40 to 50%, it has almost no heat shielding effect.

As described above, the gas sensor element 1 of the present example has a thickness T1 from the first surface 201 of the solid electrolyte body 2 to the outer surface 501 of the heater 5 in the stacking direction D of the distal end portion 11 of the gas sensor element 1, and the first The thickness T2 from one surface 201 to the outer surface 401 of the insulator 4 has a relationship of 0.7 ≦ T2 / T1 ≦ 1.6.
Thereby, thickness T2 by the side of the insulator 4 becomes thick appropriately. And when the solid electrolyte body 2 is heated by the heater 5, the heat escaping from the outer surface 401 of the insulator 4 can be reduced. As a result, the measurement gas G in the measurement gas space 61 is hardly cooled, and the temperature distribution in the measurement gas space 61 can be made difficult to occur.

Therefore, an error is less likely to occur in the oxygen ion current measured by flowing between the electrodes in the solid electrolyte body 2, and the detection accuracy by the gas sensor element 1 can be improved.
Further, the gas space 61 to be measured is located in the vicinity of the center portion in the stacking direction D in the distal end portion 11 of the gas sensor element 1. Therefore, the measurement gas G in each part in the measurement gas space 61 can be kept as uniform as possible.

  According to the gas sensor element 1 of the present example, temperature distribution is less likely to occur in the measured gas space 61, and detection accuracy can be improved.

The configuration of the distal end portion 11 of the gas sensor element 1 for reducing the heat escaping from the outer surface 401 of the insulator 4 can also be as follows.
For example, as shown in FIG. 4, a plurality of insulators 4 in the distal end portion 11 of the gas sensor element 1 can be stacked in the stacking direction D. In this case, a laminated interface 45 is formed between the insulators 4 by a minute gap. In this case, the heat conduction in the stacking direction D of the insulator 4 can be weakened by the stacking interface 45. Then, the heat of the gas G to be measured in the solid electrolyte body 2 and the gas space 61 to be measured heated by the heater 5 can be made difficult to escape to the outer surface 401 of the insulator 4 by the laminated interface 45.

  As shown in FIG. 5, a low thermal conductor 46 made of a material having a lower thermal conductivity than that of the insulator 4 may be laminated on the insulator 4 in the distal end portion 11 of the gas sensor element 1. The low thermal conductor 46 may be stacked inside the insulator 4, or may be stacked on either the inner surface or the outer surface of the insulator 4. In this case, the heat conduction in the stacking direction D of the insulator 4 can be weakened by the low heat conductor 46. The heat of the gas G to be measured in the solid electrolyte body 2 and the gas space 61 to be measured heated by the heater 5 can be made difficult to escape to the outer surface 401 of the insulator 4 by the low thermal conductor 46.

DESCRIPTION OF SYMBOLS 1 Gas sensor element 11 Front end side part 2 Solid electrolyte body 201 1st surface 202 2nd surface 4 Insulator 401 Outer surface 43 Diffusion resistor 5 Heater 501 Outer surface 501
61 Gas space to be measured

Claims (4)

Solid electrolyte body having oxygen ion conductivity and having electrodes (21, 22, 23, 25) provided on a first surface (201) as one surface and a second surface (202) as the other surface (2) and
It is laminated on the first surface (201) side of the solid electrolyte body (2) to form a measured gas space (61) into which the measured gas (G) is introduced through the diffusion resistor (43). An insulator (4);
A gas sensor element (1) comprising: a heater (5) that is laminated on the second surface (202) side of the solid electrolyte body (2) and that heats the solid electrolyte body (2),
In the stacking direction (D) of the tip side portion (11) of the gas sensor element (1) in which the electrode (21, 22, 23, 25) is provided on the solid electrolyte body (2), the first surface ( 201) to the outer surface (501) of the heater (5) and the thickness T2 from the first surface (201) to the outer surface (401) of the insulator (4) are 0.7. A gas sensor element (1) having a relationship of ≦ T2 / T1 ≦ 1.6.   The thickness (T3) in the stacking direction (D) of the insulator (4) at the front end side portion (11) of the gas sensor element (1) is equal to the thickness at the rear end side portion (12) of the gas sensor element (1). The gas sensor element (1) according to claim 1, wherein the thickness (T4) of the insulator (4) in the stacking direction (D) is larger. A plurality of the insulators (4) in the tip side portion (11) of the gas sensor element (1) are stacked in the stacking direction (D),
The gas sensor element (1) according to claim 1 or 2, wherein a laminated interface (45) is formed between the insulators (4).   On the insulator (4) in the distal end portion (11) of the gas sensor element (1), a low thermal conductor (46) made of a material having a lower thermal conductivity than the insulator (4) is laminated. The gas sensor element (1) according to any one of claims 1 to 3, wherein:

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