JP2007101353A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor capable of preventing an output characteristic from being fluctuated, and having excellent detection precision. <P>SOLUTION: The gas sensor 1 has a gas sensor element 2 for detecting a concentration of a specified gas in a measured gas, and an insulating insulator 3 for penetrating the gas sensor element 2 through an element through hole 30 to be held. The gas sensor element 2 and the insulating insulator 3 are fixed sealedly in a base end side of the element through hole 30, by an air-tight sealant 6. The gas sensor element 2 forms a sensing part 200 provided with a measured gas side electrode and a reference gas side electrode in a tip end side more than that of the insulator 3. A porous diffusion resistance layer 21 is arranged to diffuse the measured gas flowing toward the measured gas side electrode, in the sensing part 200. A cushioning sealant 4 is arranged to bury a clearance between the element through hole 30 of the insulator 3 and the gas sensor element 2, in at least tip part between the both. The cushioning sealant 4 is arranged separately from the porous diffusion resistance layer 21 along a longitudinal direction of the gas sensor element 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas sensor used for air-fuel ratio control of an internal combustion engine.

  Conventionally, a gas sensor 9 used for air-fuel ratio control or the like is installed in an exhaust system of an automobile engine. As shown in FIG. 6, the gas sensor 9 includes a cylindrical insulator 93 having an element insertion hole 930, a gas sensor element 92 sealed and fixed in the element insertion hole 930, and an insulator 93 inserted therein. A cylindrical housing 95.

  Further, the gas sensor 9 is firmly sealed and fixed between the outer side surface of the gas sensor element 92 and the inner side surface of the large-diameter portion 931 in the element insertion hole 930 with a hermetic sealing material 96. That is, since the space between the gas sensor element 92 and the element insertion hole 930 is a boundary between the reference gas side atmosphere and the measured gas side atmosphere, it is necessary to hermetically seal the two so that the two atmospheres do not mix. There is.

However, a slight gap is provided between the insulator 93 and the gas sensor element 92 in the small diameter portion 932 in order to facilitate insertion of the gas sensor element 92. For this reason, the gas sensor element 92 is fixed only on the base end side. Therefore, when receiving a large impact or vibration from the outside, the tip end side of the gas sensor element 92 swings like a pendulum (hereinafter referred to as element swing) and collides with the inner side surface of the element insertion hole 930 or stress is concentrated. For example, the gas sensor element 92 often breaks.
Therefore, a gas sensor 9 is proposed that is sealed with a buffer sealing material 94 between the inner surface of the small diameter portion 932 and the outer surface of the gas sensor element 92 (see Patent Document 1).

  According to the gas sensor 9, since the gas sensor element 92 is supported at at least two points, the rotation in the direction perpendicular to the axial direction of the gas sensor element 92 due to the element shake of the gas sensor element 92 at the distal end side of the element insertion hole 930 is achieved. Force (moment) can be reduced. Further, the shock and vibration received from the outside can be absorbed by the buffer sealing material 94. Therefore, it is possible to prevent stress concentration at the fulcrum of vibration due to element vibration and breakage of the gas sensor element 92 due to impact applied to the inner surface.

  However, in the gas sensor 9, the material of the buffer sealing material 94 soaks into the porous diffusion resistance layer 921 in the range d in which the buffer sealing material 94 and the porous diffusion resistance layer 921 are in contact with each other. May block the pores. That is, the buffer sealing material 94 contains, for example, alumina sol and aluminum nitrate as a binder in addition to alumina powder. When these binders come into contact with the porous diffusion resistance layer 921, the binder is sucked up in the porous diffusion resistance layer 921 due to capillary action, and the binder becomes aluminum oxide when the binder is volatilized by subsequent heating. The pores of the layer 921 are blocked.

Then, the pores of the porous diffusion resistance layer 921 are blocked, whereby the amount of the measurement gas that passes through the porous diffusion resistance layer 921 and is supplied to the measurement gas chamber is reduced. Therefore, the output of the gas sensor 9 with respect to the concentration of the specific gas in the gas to be measured is reduced, that is, the output characteristics are changed.
As a result, it is difficult to obtain a gas sensor having desired output characteristics, and as a result, the detection accuracy of the gas sensor element may be reduced.

JP 2002-82088 A

  The present invention has been made in view of such conventional problems, and provides a gas sensor that prevents fluctuations in output characteristics and has excellent detection accuracy.

The present invention is a gas sensor having a gas sensor element that detects the concentration of a specific gas in a gas to be measured, and an insulator that holds the gas sensor element through the element insertion hole,
The gas sensor element and the insulator are sealed and fixed by a hermetic sealing material on the base end side of the element insertion hole,
The gas sensor element is formed on the tip side of the insulator, and forms a sensing portion provided with a measured gas side electrode and a reference gas side electrode,
The sensing unit is provided with a porous diffusion resistance layer for diffusing the measurement gas toward the measurement gas side electrode,
At least the tip between the element insertion hole of the insulator and the gas sensor element is provided with a buffer sealing material that fills the gap between the two,
The buffer sealing material and the porous diffusion resistance layer are located apart from each other in the longitudinal direction of the gas sensor element. (Claim 1)

Next, the effects of the present invention will be described.
The buffer sealing material and the porous diffusion resistance layer are spaced apart from each other in the longitudinal direction of the gas sensor element. Therefore, since the buffer sealing material and the porous diffusion resistance layer do not come into contact with each other, the buffer sealing material can be prevented from soaking into the porous diffusion resistance layer. Therefore, it is possible to avoid the problem that the supply amount of the gas to be measured decreases due to clogging of the porous diffusion resistance layer. That is, fluctuations in output characteristics of the gas sensor element can be prevented, and a gas sensor with excellent detection accuracy can be obtained.

  In addition, since the buffer sealing material is disposed at least at the distal end portion between the element insertion hole of the insulator and the gas sensor element, the gas sensor element is at least at the base end side and the distal end side of the insulator. And can be fixed at two points. Therefore, it is possible to reduce the rotational force (moment) in the direction perpendicular to the axial direction of the gas sensor element due to the element deflection of the gas sensor element on the tip side of the element insertion hole. Further, the shock and vibration received from the outside can be absorbed by the buffer sealing material. As a result, breakage of the gas sensor element can be prevented.

  As described above, according to the present invention, it is possible to provide a gas sensor that prevents fluctuations in output characteristics and is excellent in detection accuracy.

  In the present invention (Claim 1), examples of the gas sensor include an air-fuel ratio sensor that is installed in an exhaust pipe of an internal combustion engine for various vehicles such as an automobile engine and used for an exhaust gas feedback system, and an oxygen concentration in the exhaust gas. There is an oxygen sensor for measuring NOx, and a NOx sensor for measuring the concentration of air pollutants such as NOx used for detecting deterioration of a three-way catalyst installed in an exhaust pipe.

Moreover, as said buffer sealing material, what mixed alumina sol and aluminum nitrate as a binder other than an alumina powder can be used, for example.
In the present specification, in the axial direction of the gas sensor element, the side exposed to the exhaust pipe of the internal combustion engine will be described as the front end side, and the opposite side as the base end side.

It is preferable that the gas sensor element has a dense ceramic interposed between an electrode lead portion continuous with the measured gas side electrode and the buffer sealing material.
In this case, the buffer sealing material can be prevented from contacting the electrode lead portion having a relatively high porosity. Therefore, the buffer sealing material can be prevented from penetrating into the porous diffusion resistance layer through the electrode lead portion.

The porous diffusion resistance layer may have a porosity of 25% or more.
In this case, the effect of the present invention can be sufficiently exerted. That is, when a porous diffusion resistance layer having a porosity of 25% or more is used for the gas sensor element, if the buffer sealing material is in contact with the porous diffusion resistance layer, the buffer to the porous diffusion resistance layer is assumed. The penetration of the sealing material becomes significant in quantity, and the output characteristics tend to fluctuate. Therefore, in the gas sensor having such a porous diffusion resistance layer having a large porosity, the effect of the present invention is particularly exerted.

  On the other hand, when the porosity of the porous diffusion resistance layer is less than 25%, since the penetration of the buffer sealing material into the porous diffusion resistance layer is relatively small, the buffer sealing material and The effect of preventing contact with the porous diffusion resistance layer is relatively small.

The porous diffusion resistance layer may have an average pore diameter of 1 μm or more.
Also in this case, the effect of the present invention can be sufficiently exhibited. That is, when the average pore diameter of the porous diffusion resistance layer is 1 μm or more, the penetration of the buffer sealing material may become significant in quantity, but by adopting the structure of the present invention to the gas sensor, Variations in output characteristics can be sufficiently suppressed.

  On the other hand, when the average pore diameter of the porous diffusion resistance layer is less than 1 μm, since the penetration of the buffer sealing material into the porous diffusion resistance layer is relatively small, the buffer sealing material and The effect of preventing contact with the porous diffusion resistance layer is relatively small.

Example 1
A gas sensor according to an embodiment of the present example will be described with reference to FIGS.
As shown in FIG. 1, the gas sensor 1 of this example includes a gas sensor element 2 that detects the concentration of a specific gas in the gas to be measured, an insulator 3 that holds the gas sensor element 2 through the element insertion hole 30, and And a housing 5 in which the insulator 3 is inserted.

As shown in FIGS. 1 and 4, the gas sensor element 2 and the insulator 3 are sealed and fixed by a hermetic sealing material 6 on the base end side of the element insertion hole 30.
Further, the gas sensor element 2 is formed with a sensing unit 200 provided with a measured gas side electrode 23 and a reference gas side electrode 25 on the tip side of the insulator 3. As shown in FIG. 2, the sensing unit 200 is provided with a porous diffusion resistance layer 21 that diffuses the measurement gas toward the measurement gas side electrode 23.

Further, as shown in FIGS. 1 and 4, a buffer sealing material 4 is disposed at a tip portion between the element insertion hole 30 of the insulator 3 and the gas sensor element 2 so as to fill a gap therebetween. The buffer sealing material 4 and the porous diffusion resistance layer 21 are spaced apart from each other in the longitudinal direction of the gas sensor element 2 (see symbol D in FIG. 1). The separation distance D can be set to 1 mm or more, for example. In this example, the surface of the gas sensor element 2 is polished and smoothed to prevent the buffer sealing material 4 from penetrating the gas sensor element 2.
The porous diffusion resistance layer 21 has a porosity of 25% or more and an average pore diameter of 1 μm or more.

The gas sensor 1 of this example is an oxygen sensor that is installed in an exhaust pipe of an internal combustion engine for various vehicles such as an automobile engine and measures the oxygen concentration in the exhaust gas.
As shown in FIGS. 2 and 3, the surface of the oxygen ion conductive solid electrolyte body 24 made of zirconia is provided with an insulating layer 22 that has an opening 220 and is made of alumina and does not transmit gas. Further, between the solid electrolytic chamber body 24 and the insulating layer 22, a measurement gas side electrode 23 made of platinum, an electrode lead portion 231 and an electrode terminal portion 232 connected thereto are provided.

As shown in FIG. 3, a gas chamber forming layer 29 to be measured is laminated on the solid electrolyte body 24. The measured gas chamber forming layer 29 is made of alumina ceramic that is electrically insulating and dense and does not allow gas to pass therethrough, and is provided with an opening 290 that constitutes the measured gas chamber 210.
A shielding layer 20 made of dense and gas-sealing alumina ceramics is laminated on the gas chamber forming layer 29 to be measured.

  The measured gas chamber forming layer 29 and the shielding layer 20 are formed so as to cover the electrode lead portion 231 continuous with the measured gas side electrode 23. As a result, the shielding layer 20 made of dense ceramic and the measured gas chamber forming layer 29 are interposed between the electrode lead portion 231 and the buffer sealing material 4.

  Further, as shown in FIGS. 1 to 4, the porous diffusion resistance layer 21 is disposed so as to be embedded in a part of the measurement gas chamber forming layer 29. That is, the end surface 211 is exposed in a direction orthogonal to the axial direction of the gas sensor element 2 and is disposed on both sides of the opening 290 so as to sandwich the opening 290 of the measured gas chamber forming layer 29. Then, the measurement gas passes through the porous diffusion resistance layer 21 and is introduced into the measurement gas chamber 210 from the end surface 211 exposed in the short direction.

  Further, for example, the porous diffusion resistance layer 21 is formed by filling a part of the green sheet of the measured gas chamber formation layer 29 before firing with the material of the porous diffusion resistance layer 21 and firing both together. can do. Moreover, after filling the material of the porous diffusion resistance layer 21 into a part of the measured gas chamber forming layer 29 after firing, firing may be performed.

  Further, as shown in FIG. 3, a reference gas side electrode 25 made of platinum and a lead portion 251 connected thereto are formed on the surface of the solid electrolyte body 24 opposite to the side where the measured gas side electrode 23 is disposed. A terminal portion 252 is provided. The terminal portion 252 is electrically connected to the terminal portion 253 provided on the measured gas chamber 210 side through the through hole 240 filled with a conductor.

  As shown in FIGS. 2 and 3, a reference gas chamber forming layer 26 made of alumina ceramic that is electrically insulating and dense and does not transmit gas is laminated on such a solid electrolyte body 24. The reference gas chamber forming layer 26 is provided with a groove 261 that functions as the reference gas chamber 260. For example, outside air (air) is introduced into the reference gas chamber 260 as a reference gas.

Then, as shown in FIGS. 2 and 3, the heater substrate 28 is laminated on the reference gas chamber forming layer 26.
The heater substrate 28 is provided with a heating element 27 that generates heat when energized, and a lead portion 271 for energizing the heating element 27 so as to face the reference gas chamber forming layer 26, and the heating element 27 and the lead portion 271. A terminal portion 272 is provided on the surface opposite to the surface provided with the.
The terminal portion 272 and the lead portion 271 are electrically connected by a through hole 280 filled with a conductor.

Next, the function and effect of this example will be described.
The buffer sealing material 4 and the porous diffusion resistance layer 21 are spaced apart in the longitudinal direction of the gas sensor element 2 as shown in FIGS. Therefore, since the buffer sealing material 4 and the porous diffusion resistance layer 21 do not come into contact with each other, the buffer sealing material 4 can be prevented from penetrating into the porous diffusion resistance layer 21. Therefore, it is possible to avoid the problem that the supply amount of the gas to be measured decreases due to the porous diffusion resistance layer 21 being clogged. That is, fluctuations in the output characteristics of the gas sensor element 2 can be prevented, and the gas sensor 1 having excellent detection accuracy can be obtained.

  As shown in FIGS. 1 and 4, since the buffer sealing material 4 is disposed on the distal end side of the insulator 3, the gas sensor element 2 is connected to the base end side and the distal end side of the insulator 3. Can be fixed with dots. Therefore, it is possible to reduce the rotational force (moment) in the direction perpendicular to the axial direction of the gas sensor element 2 due to the element shake of the gas sensor element 2 on the tip side of the element insertion hole 30. Further, the shock and vibration received from the outside can be absorbed by the buffer sealing material 4. As a result, breakage of the gas sensor element 2 can be prevented.

  Further, as shown in FIG. 3, the gas sensor element 2 is formed from a dense ceramic between an electrode lead portion 231 that is continuous with the measured gas side electrode 23 and a buffer sealing material 4 (not shown in FIG. 3). Since the shielding layer 20 and the measured gas chamber forming layer 29 are interposed, the buffer sealing material 4 can be prevented from contacting the electrode lead portion 231 having a relatively high porosity. Therefore, it is possible to prevent the buffer sealing material 4 from penetrating into the porous diffusion resistance layer 21 through the electrode lead portion 231.

  Further, the porous diffusion resistance layer 21 in the gas sensor 1 of the present example has a porosity of 25% or more and an average pore diameter of 1 μm or more. In such a case, the gas sensor 1 has the above-described structure in the present invention. In particular, the effects of the present invention can be exhibited.

  As described above, according to this example, it is possible to provide a gas sensor that prevents fluctuations in output characteristics and is excellent in detection accuracy.

(Example 2)
In this example, as shown in FIG. 5, the opening 290 of the measured gas chamber forming layer 29 is covered on the surface of the measured gas chamber forming layer 29 opposite to the side where the solid electrolyte body 24 is disposed. This is an example of the gas sensor 1 in which a porous diffusion resistance layer 21 is laminated. Further, the porous diffusion resistance layer 21 has a shield having an axial length and width substantially equal to those of the porous diffusion resistance layer 21 on the surface opposite to the side where the measured gas chamber forming layer 29 is disposed. Layer 20 is laminated.
Also in this example, the gas sensor 1 has a configuration in which the buffer sealing material 4 (not shown in FIG. 5) and the porous diffusion resistance layer 21 are spaced apart.
In addition, the configuration and operational effects are the same as those of the first embodiment.

FIG. 3 is a cross-sectional explanatory view of a gas sensor in the first embodiment. Sectional explanatory drawing of the gas sensor element corresponded in the AA cross section of FIG. FIG. 3 is a perspective development view of the gas sensor element in the first embodiment. Sectional explanatory drawing which shows the assembly | attachment state of the gas sensor element and an insulator in Example 1. FIG. FIG. 6 is a perspective development view of a gas sensor element in Example 2. Sectional explanatory drawing of the gas sensor in a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Gas sensor element 21 Porous diffused resistance layer 23 Gas side electrode to be measured 24 Reference gas side electrode 200 Sensing part 3 Insulator 30 Element insertion hole 4 Buffer sealing material 6 Sealing sealing material

Claims (4)

A gas sensor having a gas sensor element for detecting the concentration of a specific gas in a gas to be measured, and an insulator for holding the gas sensor element through the element insertion hole,
The gas sensor element and the insulator are sealed and fixed by a hermetic sealing material on the base end side of the element insertion hole,
The gas sensor element is formed on the tip side of the insulator, and forms a sensing portion provided with a measured gas side electrode and a reference gas side electrode,
The sensing unit is provided with a porous diffusion resistance layer for diffusing the measurement gas toward the measurement gas side electrode,
At least the tip between the element insertion hole of the insulator and the gas sensor element is provided with a buffer sealing material that fills the gap between the two,
The gas sensor, wherein the buffer sealing material and the porous diffusion resistance layer are spaced apart from each other in the longitudinal direction of the gas sensor element.   2. The gas sensor according to claim 1, wherein the gas sensor element comprises a dense ceramic interposed between an electrode lead portion continuous with the gas to be measured side electrode and the buffer sealing material.   3. The gas sensor according to claim 1, wherein the porous diffusion resistance layer has a porosity of 25% or more.   The gas sensor according to claim 1, wherein the porous diffusion resistance layer has an average pore diameter of 1 μm or more.

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