JP2011247790A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor capable of preventing cracks of a gas sensor element due to condensed water without affecting sensor output characteristics.SOLUTION: The gas sensor includes a housing, an insulator 11, and a laminated type gas sensor element 2. The gas sensor element 2 includes a solid electrolyte 21, a measurement target gas side electrode 22, a reference gas side electrode 23, a measurement target gas chamber 24, a porous diffusion resistance layer 25, and a shielding layer 26. On the shielding layer 26, a drainage hole 261 for discharging moisture from the porous diffusion resistance layer 25 is formed at an axial direction position between the distal end of the insulator 11 and the proximal end of the measurement target gas chamber 24. When the axial direction length of the measurement target gas chamber 24 is defined as L0 and an axial direction distance between the measurement target gas chamber 24 and the drainage hole 261 is defined as L1, L1/LO≥0.4 is satisfied.

Description

  The present invention relates to a gas sensor for detecting a specific gas concentration in a gas to be measured.

For example, a gas sensor such as an A / F sensor is provided in an exhaust system of a vehicle internal combustion engine such as an automobile engine, the air-fuel ratio is detected from the oxygen concentration in the exhaust gas, and the combustion control of the engine is performed using this. There is (exhaust gas feedback system).
A gas sensor used in such an exhaust gas feedback system includes a gas sensor element that is exposed to a gas to be measured such as exhaust gas and detects a specific gas concentration (oxygen concentration) in the gas to be measured.

  As the gas sensor element, an oxygen ion conductive solid electrolyte body, a measured gas side electrode and a reference gas side electrode provided on one surface and the other surface of the solid electrolyte body, and the measured gas side A gas chamber to be measured, which is a space in which an electrode is disposed, a porous diffusion resistance layer that covers the gas chamber to be measured and transmits the gas to be measured, and a dense shielding layer that covers the porous diffusion resistance layer There are some (Patent Documents 1 and 2).

JP 2007-86051 A Japanese Patent No. 4157290

However, the gas sensor has the following problems.
That is, when the internal combustion engine is cold started, the exhaust gas may be introduced into the gas sensor element together with moisture. In the vicinity of the tip of the gas sensor element, the moisture does not stay because it is at a high temperature, but because the part on the base end side from the tip of the gas sensor element, such as the part held by the insulator, does not become sufficiently hot, Moisture introduced with the exhaust gas may condense. Such a phenomenon can occur particularly in an internal combustion engine having a low exhaust gas temperature, such as a diesel engine.

  Then, condensed water (condensation water) may enter the gas chamber to be measured through the porous diffusion resistance layer. At this time, the condensed water in the gas chamber to be measured is boiled by the heater for heating the gas sensor element, the internal pressure of the gas chamber to be measured increases rapidly, and the solid electrolyte body may be cracked (FIG. 6). FIG. 7).

  In order to cope with this problem, it is conceivable that a drain hole for releasing moisture from the porous diffusion resistance layer is provided in the shielding layer. However, if the position is close to the gas chamber to be measured, the drain hole Therefore, the gas to be measured is introduced into the gas chamber to be measured, and the sensor output characteristics of the gas sensor change. Therefore, especially in the exhaust gas feedback system as described above, when adopting a gas sensor having a drain hole instead of a gas sensor having no drain hole, the system is changed according to the change in sensor output characteristics. The problem of being forced arises.

  Patent Documents 1 and 2 disclose a configuration in which a hole is provided in the shielding layer. These are holes for taking the gas to be measured into the gas chamber to be measured, and are formed in the vicinity of the gas chamber to be measured. ing. Therefore, even if moisture can be discharged through this hole, the problem of change in sensor output characteristics occurs as described above.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a gas sensor that can prevent the gas sensor element from being cracked due to condensed water without affecting the sensor output characteristics.

The present invention is a gas sensor having a cylindrical housing, a cylindrical insulator held inside the housing, and a laminated gas sensor element inserted and fixed to the insulator,
The gas sensor element includes an oxygen ion conductive solid electrolyte body, a measured gas side electrode and a reference gas side electrode provided on one surface and the other surface of the solid electrolyte body, and the measured gas side electrode, respectively. A measurement gas chamber that is a space in which the measurement gas chamber is disposed, a porous diffusion resistance layer that covers the measurement gas chamber and transmits the measurement gas, and a dense shielding layer that covers the porous diffusion resistance layer ,
The shielding layer is formed with a drain hole for releasing moisture from the porous diffusion resistance layer at an axial position between the tip of the insulator and the base end of the gas chamber to be measured. ,
L1 / L0 ≧ 0.4 is satisfied, where L0 is the axial length of the gas chamber to be measured and L1 is the axial distance between the gas chamber to be measured and the drain hole. It exists in a gas sensor (Claim 1).

The gas sensor is provided with the drain hole in the shielding layer of the gas sensor element. Thereby, even if the condensed water generated around the portion of the gas sensor element held by the insulator penetrates to the tip side through the porous diffusion resistance layer, the condensed water can be discharged from the drain hole. .
Therefore, it is possible to prevent the condensed water from entering the measured gas chamber, and it is possible to prevent the condensed water from boiling in the measured gas chamber. As a result, it is possible to prevent the gas sensor element from being cracked due to the condensed water.

  Further, the position of the drain hole is a position where the axial length L0 and the axial distance L1 satisfy L1 / L0 ≧ 0.4. Therefore, it is possible to prevent the drain hole from affecting the sensor output characteristics of the gas sensor. That is, the water drain hole is formed at a position sufficiently away from the measured gas chamber so as to satisfy the above condition, so that the amount of the measured gas introduced from the drain hole into the measured gas chamber is sufficiently large. Can be reduced. As a result, a change in sensor output characteristics due to the provision of the drain hole can be prevented.

  As described above, according to the present invention, it is possible to provide a gas sensor that can prevent the gas sensor element from being cracked due to condensed water without affecting the sensor output characteristics.

FIG. 3 is a cross-sectional view of a gas sensor element in Example 1. FIG. 3 is a plan view of a gas sensor element in the first embodiment. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. FIG. 3 is a cross-sectional view of the gas sensor in the first embodiment. Sectional explanatory drawing explaining the effect in Example 1. FIG. Cross-sectional explanatory drawing explaining the movement of condensed water when not providing a drain hole. Cross-sectional explanatory drawing explaining the boiling of condensed water when not providing a drain hole. FIG. 6 is a diagram illustrating a relationship between a formation position of a drain hole and sensor output characteristics in Example 2. FIG. 10 is a diagram showing the relationship between the diameter of the drain hole and the amount of moisture reaching the measured gas chamber in Example 3. The diagram which shows the relationship between the diameter of the drain hole in Example 4, and the bending strength of a gas sensor element. The top view of the gas sensor element of the variation which changed variously the shape etc. of the drain hole in Example 5. FIG.

In the present invention, examples of the gas sensor include an A / F sensor that measures an air-fuel ratio based on a limit current value corresponding to the oxygen concentration in the gas to be measured, an oxygen sensor that measures the oxygen concentration in the gas to be measured, and an exhaust gas. There are NOx sensors and the like for checking the concentration of atmospheric pollutants such as NOx used for detecting deterioration of a three-way catalyst installed in a pipe.
In the present application, the side where the gas sensor is inserted into the exhaust system or the like of the internal combustion engine will be described as the front end side, and the opposite side as the base end side.
If the axial length L0 and the axial distance L1 have a relationship of L1 / L0 <0.4, the drain hole is too close to the gas chamber to be measured, and the drain hole is a sensor output characteristic. May be affected.

Moreover, it is preferable that the opening area of the drain hole corresponds to an area of a circle having a diameter of 1 mm or more.
In this case, the condensed water can be sufficiently discharged from the drain hole, and the cracking of the gas sensor element can be sufficiently prevented.

Moreover, it is preferable that the said drain hole is formed in a part of width direction in the said shielding layer (Claim 3).
In this case, condensed water can be discharged while ensuring the strength of the gas sensor element. That is, if the drainage hole is formed to be large over the entire width direction of the shielding layer, the bending strength of the gas sensor element may be reduced. As described above, the drainage hole is arranged in the width direction of the shielding layer. If it is not formed in the entire area in the width direction, sufficient bending strength can be secured.

Moreover, it is preferable that the opening area of the drain hole corresponds to an area of a circle having a diameter of 1.8 to 2.0 mm.
In this case, it is possible to more reliably prevent the gas sensor element from being cracked due to the condensed water, and to sufficiently ensure the bending strength of the gas sensor element.

Moreover, it is preferable that the said gas sensor detects the specific gas concentration in the to-be-measured gas below 600 degreeC.
In this case, the effect of the present invention of preventing the gas sensor element from being cracked due to the condensed water can be further exhibited. That is, for example, when the temperature of the gas to be measured such as exhaust gas of a diesel engine is as low as 600 ° C. or less, condensed water is likely to be generated in the gas sensor element. Therefore, by applying the present invention to such a gas sensor, cracking of the gas sensor element due to condensed water can be effectively prevented.

Example 1
A gas sensor according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 4, the gas sensor 1 of this example includes a cylindrical housing 10, a cylindrical insulator 11 held inside the housing 10, and a stacked gas sensor inserted and fixed to the insulator 11. Element 2.

  As shown in FIGS. 1 and 3, the gas sensor element 2 includes an oxygen ion conductive solid electrolyte body 21, a measured gas side electrode 22 provided on one surface and the other surface of the solid electrolyte body 21, and A reference gas side electrode 23, a measurement gas chamber 24 that is a space in which the measurement gas side electrode 22 is disposed, a porous diffusion resistance layer 25 that covers the measurement gas chamber 24 and transmits the measurement gas; And a dense shielding layer 26 that covers the porous diffusion resistance layer 25.

A drain hole 261 for releasing moisture from the porous diffusion resistance layer 25 is formed in the shielding layer 26 at an axial position between the distal end of the insulator 11 and the proximal end of the measured gas chamber 24. Yes.
As shown in FIG. 2, when the axial length of the measured gas chamber 24 is L0 and the axial distance between the measured gas chamber 24 and the drain hole 261 is L1, L1 / L0 ≧ 0.4 is satisfied. Fulfill.

The opening area of the drain hole 261 corresponds to the area of a circle having a diameter of 1 mm or more. Further, as shown in FIG. 2, the drain hole 261 is formed in a part of the shielding layer 26 in the width direction. That is, the drain hole 261 is not formed over the entire width direction of the shielding layer 26 but is formed in a state where the drain hole 261 does not divide the shielding layer 26 in the axial direction.
More preferably, the opening area of the drain hole 261 corresponds to the area of a circle having a diameter of 1.8 to 2.0 mm. In this example, the drain hole 261 is circular. Therefore, the diameter of the drain hole 261 is 1.8 to 2.0 mm.

The gas sensor element 2 in the gas sensor 1 of the present example includes the solid electrolyte body 21, the measured gas side electrode 22, the reference gas side electrode 23, the measured gas chamber 24, the porous diffusion resistance layer 25, and the shielding layer 26 described above. As shown in FIGS. 1 and 3, the following components are provided.
That is, a reference gas chamber forming layer 28 for forming a reference gas chamber 27 that is a space in which the reference gas side electrode 23 is disposed is laminated on the surface of the solid electrolyte body 21 where the reference gas side electrode 23 is formed. Has been. A heater 29 for heating the gas sensor element 2 is embedded in the reference gas chamber forming layer 28.
Further, a spacer layer 241 for forming the gas chamber 24 to be measured is interposed between the solid electrolyte body 21 and the porous diffusion resistance layer 25.

  Further, the porous diffusion resistance layer 25 and the shielding layer 26 are formed from the tip of the gas sensor element 2 to a portion held by the insulator 11. Therefore, the portion on the tip side of the insulator 11, that is, the portion exposed to the measurement gas in the gas sensor element 2, is porous on the entire surface of the solid electrolyte body 21 on the side where the measurement gas side electrode 22 is arranged. A quality diffusion resistance layer 25 and a shielding layer 26 are formed. However, as a matter of course, the porous diffusion resistance layer 25 is exposed at the portion of the drain hole 261.

  Among the ceramic layers constituting the gas sensor 2, the solid electrolyte body 21 is mainly composed of zirconia, and the other ceramic layers are mainly composed of alumina. Moreover, the porosity of the porous diffusion resistance layer 25 is 10 to 20%. Further, the measured gas side electrode 22 and the reference gas side electrode 23 are made of platinum.

Further, as shown in FIG. 2, the measured gas chamber 24 has a shape that is long in the axial direction, and both end portions thereof are semicircular.
An example of specific dimensions of the gas sensor element 2 with respect to the tip of the insulator 11 is shown below.
First, the protruding length L4 of the gas sensor element 2 from the insulator 11 is 15 mm. The width W of the gas sensor element 2 is 4.5 mm, and the thickness T is 2.0 mm (see FIG. 1).

The axial length L0 of the measured gas chamber 24 is 7.8 mm, and the axial distance L1 between the measured gas chamber 24 and the drain hole 261 is 3.35 mm. The axial distance L2 from the tip of the gas sensor element 2 to the measured gas chamber 24 is 1.45 mm. And the axial direction distance L3 (= L2 + L0 + L1) from the front-end | tip of the gas sensor 2 to the drain hole 261 is 12.6 mm. The diameter of the drain hole 261 is 1.8 mm.
Further, the gas chamber 24 to be measured and the drain hole 261 are disposed at the center in the width direction of the gas sensor element 2.

  As shown in FIG. 4, the gas sensor 1 includes an insulator 11 that inserts and holds the gas sensor element 2 inside, and a housing 10 that inserts and holds the insulator 11 inside. On the front end side of the housing 10, a front end cover 12 having a double structure formed so as to cover the front end portion of the gas sensor element 2 is fixed. The distal end cover 12 is formed with an introduction hole 121 for introducing a gas to be measured inside.

On the other hand, a proximal end cover 13 that covers the proximal end portion of the gas sensor element 2 is fixed to the proximal end side of the housing 10. Inside the base end side cover 13, a contact terminal 14 that is brought into contact with a terminal provided at a base end portion of the gas sensor element 2 and a terminal insulator 15 that holds the contact terminal 14 are arranged. Further, the base end portion of the base end side cover 13 is closed by a rubber bush 16, and an external lead 141 connected to the contact terminal 14 passes through the rubber bush 16. Further, at the position in the axial direction between the terminal insulator 15 and the rubber bush 16, the base end side cover 13 is provided with a ventilation portion 131 for introducing outside air into the inside.
Further, the housing 10 is formed with a mounting screw portion 101 for screwing the female screw portion provided on the pipe wall of the exhaust pipe to attach the gas sensor 1 to the exhaust pipe.

  The gas sensor 1 detects, for example, a specific gas concentration in a gas to be measured at 600 ° C. or lower at normal times. Specifically, the gas sensor 1 is installed in an exhaust system of a diesel engine, for example, and is used as an A / F sensor for measuring an air-fuel ratio by detecting an oxygen concentration in the exhaust gas. In the exhaust system of the diesel engine, the exhaust gas temperature becomes, for example, 600 ° C. or less during normal operation except during regeneration of the DPF (diesel particulate filter).

  Thus, when the gas sensor 1 is installed in the exhaust system of a diesel engine having a relatively low exhaust gas temperature, condensed water is likely to be generated. Therefore, when installed in an exhaust system of an internal combustion engine where the temperature of the gas to be measured (exhaust gas) is 600 ° C. or less, the gas sensor 1 of the present invention can sufficiently exhibit its effect. Furthermore, when the temperature of the gas to be measured (exhaust gas) is installed in an exhaust system of an internal combustion engine having a temperature of 500 ° C. or less, the gas sensor 1 of the present invention can further exert its effect.

Next, the function and effect of this example will be described.
The gas sensor 1 is formed by providing a drain hole 261 in the shielding layer 26 of the gas sensor element 2. As a result, as shown in FIG. 5, even if the condensed water M generated around the portion of the gas sensor element 2 held by the insulator 11 penetrates to the tip side through the porous diffusion resistance layer 25, the drainage hole 261 The condensed water M can be discharged.
Therefore, the condensed water M can be prevented from entering the measured gas chamber 24, and the condensed water M in the measured gas chamber 24 can be prevented from boiling. As a result, the gas sensor element 2 can be prevented from cracking due to the condensed water M.

That is, as shown in FIG. 6, if the drain hole 261 is not provided, the condensed water M condensed on the portion closer to the proximal end than the distal end portion of the gas sensor element 2 such as a portion held by the insulator 11 of the gas sensor element 2. However, there is a possibility that the gas diffuses through the porous diffusion resistance layer 25 and enters the measured gas chamber 24. At this time, as shown in FIG. 7, the condensed water M in the measured gas chamber 24 is boiled by the heater 29, and the internal pressure of the measured gas chamber 24 rapidly increases, and the solid electrolyte body 21 may be cracked. There is.
Therefore, as shown in FIG. 5, by providing the drain hole 261 in the shielding layer 26, the condensed water M is discharged from the drain hole 261 as described above, and the solid electrolyte body 21 is cracked due to the condensed water. Can be prevented.

  Further, as shown in FIG. 2, the position of the drain hole 261 is a position where the axial length L0 and the axial distance L1 satisfy L1 / L0 ≧ 0.4. Therefore, it is possible to prevent the drain hole 261 from affecting the sensor output characteristics of the gas sensor 1. That is, the measured gas introduced from the drain hole 261 into the measured gas chamber 24 by forming the drain hole 261 sufficiently away from the measured gas chamber 24 so as to satisfy the above condition. Can be sufficiently reduced. As a result, it is possible to prevent a change in sensor output characteristics due to the provision of the drain hole 261 (see Example 2 described later).

  The drain hole 261 corresponds to the area of a circle having a diameter of 1 mm or more. In this example, the diameter of the circular drain hole 261 is 1 mm or more. Thereby, condensed water can fully be discharged | emitted from the drain hole 261, and the crack of the gas sensor element 2 can fully be prevented (refer Example 3 mentioned later).

  Moreover, since the drain hole 261 is formed in a part of the shielding layer 26 in the width direction, the condensed water can be discharged while ensuring the strength of the gas sensor element 2. That is, if the drainage hole 261 is formed to be large over the entire width direction of the shielding layer 26, the bending strength of the gas sensor element 2 may be reduced. As described above, the drainage hole 261 in the width direction of the shielding layer 26 may be reduced. If it is formed in a part and not in the entire region in the width direction, sufficient bending strength can be ensured (see Example 4 described later).

  The opening area of the drain hole 261 corresponds to the area of a circle having a diameter of 1.8 to 2.0 mm. In this example, the diameter of the circular drain hole 261 is 1.8 to 2.0 mm. Thereby, while preventing the crack of the gas sensor element 2 resulting from condensed water more reliably, the bending strength of the gas sensor element 2 can fully be ensured.

  Further, when the gas sensor 1 detects a specific gas concentration in the gas to be measured at 600 ° C. or lower, as described above, the effect of the present invention of preventing the gas sensor element 2 from being cracked due to condensed water is obtained. Can be more effective.

  As described above, according to this example, it is possible to provide a gas sensor that can prevent the gas sensor element from being cracked due to condensed water without affecting the sensor output characteristics.

(Example 2)
In this example, as shown in FIG. 8, the relationship between the formation position of the drain hole 261 and the sensor output characteristics is examined.
First, as a sample, except for the position where the drain hole 261 is formed, the gas sensor 1 (sample 1) having the specific dimensional relationship shown in the first embodiment and the tip portion of the gas sensor element 2 (tip than the insulator 11) A gas sensor 1 (sample 2) provided with a gas sensor element 2 in which the width W of the side portion was changed to 3.8 mm was prepared.

  For Sample 1 and Sample 2, L1 and L0 were each in the range of 0.35 to 0.6, and six types different in increments of 0.05 were prepared, for a total of 12 types. Furthermore, as a comparative sample 1 and a comparative sample 2 corresponding to the sample 1 and the sample 2, a gas sensor (see FIG. 6) including a gas sensor element without the drain hole 261 was produced. Except for the absence of the drain hole 261, the comparative sample 1 and the comparative sample 2 have the same configurations as the sample 1 and the sample 2, respectively.

  These gas sensors were attached to the exhaust system of a diesel engine, and the engine was operated in an air-fuel ratio (A / F) 18 state. The sensor when the gas sensor is exposed to exhaust gas (measured gas) and a voltage of 0.4 V is applied between the electrodes of the gas sensor element 2 (between the measured gas side electrode 22 and the reference gas side electrode 23). The output was measured. In addition, the temperature of the heater 29 was 750 degreeC. The results of measuring each sample five times are plotted in FIG. Plot ● is data of sample 1 or comparative sample 1, and plot ◆ is data of sample 2 or comparative sample 2. Moreover, the plot group enclosed with the broken line described in the left end of FIG. Curves S1 and S2 are change curves of sensor output obtained by smoothly connecting the plots of Sample 1 and Sample 2, respectively.

As can be seen from FIG. 8, when L1 / L0 is 0.35, the sensor outputs of samples 1 and 2 are higher than those of comparative samples 1 and 2, respectively. On the other hand, when L1 / L0 is 0.4 or more, both of the change curves L1 and L2 become sideways, the sensor output hardly changes, and is equivalent to the sensor outputs of the comparative samples 1 and 2.
This is because when L1 / L0 is 0.35, the drainage hole 261 affects the sensor output characteristics, but if the drainage hole 261 is formed at a position satisfying L1 / L0 ≧ 0.4, the sensor It shows that the output characteristics can be prevented from being affected.

(Example 3)
In this example, as shown in FIG. 9, the relationship between the diameter of the drain hole 261 and the amount of moisture reaching the measured gas chamber 24 is simulated.
The gas sensor used for the simulation is the gas sensor 1 shown in the first embodiment. However, the diameter of the drain hole 261 was changed variously between 0 and 2.5 mm.
The axial lengths of the porous diffusion resistance layer 25 and the shielding layer 26 are 19 mm, and the axial length from the base end of the measured gas chamber 24 to the base ends of the porous diffusion resistance layer 25 and the shielding layer 26 is 9 mm. .75 mm. The thickness of the porous diffusion resistance layer 25 was 0.24 mm, and the porosity was 13%.

Here, it was assumed that 1.37 mg of condensed water was generated in the gas sensor element 2. This is the amount of water assuming that the porous diffusion resistance layer 25 on the base end side of the measured gas chamber 24 absorbs water. As a result of simulating the amount of condensed water reaching the gas chamber to be measured 24 (the amount of water reached) under the same environment as the exhaust system of an actual diesel engine, the diameter of the drain hole 261 is shown in FIG. It was found that the amount of water reached changed according to the conditions. In the figure, the plot ◆ represents the calculated amount of water reached.
And if the diameter of the drain hole 261 was 1.0 mm or more, it turned out that it can be less than 0.01 mg which is the reached | attained water content of the grade which the solid electrolyte body 21 does not crack.

Here, 0.01 mg, which is the amount of water that reaches the extent that the solid electrolyte body 21 does not break, was calculated as follows.
That is, first, as a result of measuring the cracking strength of the solid electrolyte body 21 by a pressure test, a value of 4 MPa was obtained. Therefore, in order to prevent the solid electrolyte body 21 from being broken, the internal pressure of the measured gas chamber 24 should be 4 MPa or less. That is, when moisture enters the gas chamber 24 to be measured and boiled, the amount of water that causes the internal pressure of the gas chamber 24 to be 4 MPa or less may be calculated. The amount of water is determined by substituting the upper limit internal pressure 4 MPa, the volume of the gas chamber 24 to be measured, and the absolute temperature of the gas chamber 24 to be measured when the gas sensor 1 is used into the gas equation of state. Can be obtained by multiplying this by the molecular weight of water. As a result, if the amount of moisture reached is 0.01 mg or less, it can be calculated that the solid electrolyte body 21 is not broken.

  And it turns out by the said simulation that if the diameter of the drain hole 261 is 1 mm or more, it will be understood that the amount of moisture reached is less than 0.01 mg, so that cracking of the solid electrolyte body 21 can be prevented.

Example 4
In this example, as shown in FIG. 10, the relationship between the diameter of the drain hole 261 and the bending strength of the gas sensor element 2 is examined.
That is, a gas sensor having the same structure as that of the gas sensor 1 shown in Example 1 was used, in which the diameter of the drain hole 261 was variously changed between 0 and 4.5 mm.

  The gas sensor having a water drain hole 261 with a diameter of 0 mm is a gas sensor (see FIG. 6) that does not have the water drain hole 261. If the strength is equal to the bending strength of the gas sensor, the strength is due to the provision of the water drain hole 261. It can be judged that there is no decline. Therefore, the bending strength of the gas sensor element 2 that does not have the drain hole 261 was measured a plurality of times, the average value was set to 100% strength ratio, and the strength of each sample with respect to the average strength value was expressed as the strength ratio. This is shown in FIG. Multiple tests were performed for each level.

Here, the bending strength of each sample was measured using a pendulum test disclosed in JP-A No. 2002-296214.
As can be seen from FIG. 10, the strength ratio was almost 100% for any sample in which the diameter of the drain hole 261 was 1 to 2.4 mm, and no strength reduction was observed.

On the other hand, when the diameter of the drain hole 261 is 4.5 mm, the strength ratio is greatly reduced. This 4.5 mm is the same as the width W of the gas sensor element 2 and is the same as the width of the shielding layer 26. That is, it can be seen that when the drain hole 261 is formed over the entire width of the shielding layer 26, the bending strength of the gas sensor element 2 is greatly reduced.
From the above results, in order to ensure the bending strength of the gas sensor element 2, it is necessary to form the drain hole 261 not in the whole width direction of the shielding layer 26 but in a part in the width direction. I understand that.

(Example 5)
This example is a variation of the gas sensor element 2 in which the shape or the like of the drain hole 261 is changed as shown in FIG.
A gas sensor element 2 a shown in FIG. 11A is formed by forming drain holes 261 long in the width direction of the shielding layer 26. In this case, it becomes easy to release moisture from the drain hole 261 over a wide range in the width direction of the gas sensor element 2a, and the cracking of the solid electrolyte body 21 due to the condensed water can be prevented more reliably.

A gas sensor element 2b shown in FIG. 11B is formed by forming a drain hole 261 in a substantially rectangular shape.
A gas sensor element 2c shown in FIG. 11C is formed by forming drain holes 261 at three locations. The three drain holes 261 are arranged side by side in the width direction of the shielding layer 26. As described above, a plurality of drain holes 261 may be formed.
A gas sensor element 2d shown in FIG. 11D is formed by forming a drain hole 261 in a diamond shape.
Also in the gas sensor elements 2b, 2c, and 2d shown in FIGS. 11B, 11C, and 11D, moisture in the gas sensor element 2 can be easily released.
The rest of the configuration is the same as that of the first embodiment, and the same effects as those of the first embodiment are achieved.

DESCRIPTION OF SYMBOLS 1 Gas sensor 11 Insulator 2 Gas sensor element 21 Solid electrolyte body 22 Gas to be measured electrode 23 Reference gas side electrode 24 Gas chamber to be measured 25 Porous diffusion resistance layer 26 Shielding layer 261 Drain hole

Claims (4)

A gas sensor having a cylindrical housing, a cylindrical insulator held inside the housing, and a laminated gas sensor element inserted and fixed to the insulator,
The gas sensor element includes an oxygen ion conductive solid electrolyte body, a measured gas side electrode and a reference gas side electrode provided on one surface and the other surface of the solid electrolyte body, and the measured gas side electrode, respectively. A measurement gas chamber that is a space in which the measurement gas chamber is disposed, a porous diffusion resistance layer that covers the measurement gas chamber and transmits the measurement gas, and a dense shielding layer that covers the porous diffusion resistance layer ,
The shielding layer is formed with a drain hole for releasing moisture from the porous diffusion resistance layer at an axial position between the tip of the insulator and the base end of the gas chamber to be measured. ,
L1 / L0 ≧ 0.4 is satisfied, where L0 is the axial length of the gas chamber to be measured and L1 is the axial distance between the gas chamber to be measured and the drain hole. Gas sensor.   2. The gas sensor according to claim 1, wherein an opening area of the drain hole corresponds to an area of a circle having a diameter of 1 mm or more.   3. The gas sensor according to claim 1, wherein the drain hole is formed in a part of the shielding layer in a width direction.   The gas sensor according to any one of claims 1 to 3, wherein an opening area of the drain hole corresponds to an area of a circle having a diameter of 1.8 to 2.0 mm.

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