JP2003194767A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor where an element is completely protected from condensed water or the like by a relatively simple method without changing the structure of the element. <P>SOLUTION: The gas sensor 1 comprises a flat ceramic element 2 where a detection section D is formed at the front end side, and double protectors 6a and 6b for protecting the flat ceramic element 2 from moisture and oil content contained in the condensed water or gas to be detected. On one surface of the detection section D, a protection layer 24 is provided so that an electrode 25 for composing the gas detection surface is covered. Then, at a sidewall section W3 of the inner protector 6b, a gas-introducing hole 60 is formed at an angle position that faces the protection layer 24. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxygen sensor, HC
The present invention relates to a gas sensor such as a sensor or a NOx sensor for detecting a detected component in a gas to be measured.

[0002]

2. Description of the Related Art As a gas sensor as described above, a detection element for detecting a component to be detected has a detection element formed at its front end.
A structure in which a metal casing is arranged inside is known. In particular, in recent years, a gas sensor having a plate-shaped element with a built-in heater, which places importance on shortening the time until the element becomes active, is becoming the mainstream. In such a gas sensor, a protector is provided to cover the detection unit located in the measurement atmosphere. A gas flow hole is formed in the side wall of the protector, and a gas to be measured such as exhaust gas is introduced into the protector through the gas flow hole and contacts the detector.

By the way, the plate-shaped detecting element is inferior in thermal shock resistance to the cylindrical one. That is, when water or oil adheres, cracks or breaks easily occur. Therefore, it is usual to cover the gas detection surface with a protective layer resistant to thermal shock to protect it. On the other hand, with regard to the protector that protects the detection unit, the detection unit protects against water droplets, oil droplets, dirt, etc. in the gas to be measured, as well as intrusion of condensed water condensed on the wall surface of the protector and the internal space. To enhance the protection function,
A protector having a double structure composed of two cylindrical parts inside and outside is also often used. In such a dual structure protector, gas inlets are formed in the side walls of the inner and outer protectors, respectively, and the gas to be measured first passes through the gas inlet of the outer protector and then the gas inlet of the inner protector to reach the detection portion. To reach.

[0004]

However, in most cases, the protective layer is formed on the gas detection surface of the detection element, but no consideration is given to other surfaces. Therefore, in a measurement atmosphere in which a large amount of condensed water or the like is generated, there is a possibility that the detection element cannot be completely protected by simply doubling the protector. It is not preferable that there is no method of covering the entire detection part with a protective layer, but it is very troublesome and increases the manufacturing process and manufacturing cost.

Therefore, an object of the present invention is to provide a gas sensor in which the element is completely protected from condensed water and the like by a relatively simple method without changing the structure of the element.

[0006]

In order to solve the above problems, a gas sensor according to the present invention is a gas sensor of the present invention, and a detection section formed on the front end side in the axial direction of a detection element, and a cylinder provided so as to cover the detection section. In a gas sensor including a cylindrical inner protector and a cylindrical outer protector arranged outside the inner protector, the detection unit has an electrode formed on the surface of a plate-shaped solid electrolyte body and covers the electrode. The protective layer is provided in a shape, and has a structure in which the ceramic heater is adjacent to the back side, the side wall of the outer protector, a gas flow hole for flowing the gas to be detected inside and outside itself is formed,
On the side wall portion of the inner protector, while a gas introduction hole for introducing the gas to be detected into the detection space inside itself is formed,
The side with the protective layer in the plate thickness direction of the solid electrolyte body is defined as the front side of the gas sensor, and further, in the cross section perpendicular to the axial direction including the detection part, in the plate thickness direction of the electrode and the protective layer covering it. When a vertical joint boundary line is defined and the side wall portion of the inner protector is divided into two parts along an imaginary plane that includes the joint boundary line and is parallel to the axis, the gas introduction hole is formed only on one side located on the front side. It is characterized by being

The present invention described above includes a so-called TF (Thich Film) type detection element having a gas detection ability directionally dependent,
A gas sensor having a double structure protector,
In particular, the position of the gas introduction hole to be formed in the side wall portion of the inner protector is set within a specific range. Specifically, in the detection part of the detection element, the surface side that is the gas detection surface is provided with a protective layer that is resistant to thermal shock, so the gas introduction hole formed in the inner protector should be as close to the protective layer side as possible. To form. By doing so, the ceramic heater side (the side opposite to the protective layer) becomes a blind zone when viewed from the gas introduction hole, and the side surface of the element does not at least face the gas introduction hole. If so, even when condensed water generated on the inner peripheral surface of the outer protector or water or oil contained in the gas to be detected enters the detection space in the inner protector, at least the side surface of the detection unit or It is possible to prevent or suppress their adhesion to the surface on the ceramic heater side. Therefore, it is possible to provide a gas sensor having excellent durability, which is free from the problem that the detection element is cracked or cracked by thermal shock. In particular, the effect becomes more remarkable as the atmosphere becomes more likely to generate condensed water. Further, since it is not necessary to change the structure of the element, it can be manufactured at a very low cost.

The gas to be detected introduced into the gas detection space from the gas introduction hole formed in the side wall portion may be discharged to the outside through a gas discharge hole formed in the front end portion of the inner protector, for example. . In addition, at least the side surface of the element on which the protective layer is not formed does not face the gas introduction hole, so that the design is easy if the interface between the protective layer and the electrode is used as a reference. In practice, since the electrode has a thin film shape on the order of micrometers, the interface between the protective layer and the solid electrolyte body can be used as the junction boundary line.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the examples shown in the drawings. FIG. 1 shows an oxygen sensor 1 for detecting the oxygen concentration in the exhaust gas of an automobile or the like as an embodiment of the gas sensor of the present invention. This oxygen sensor is commonly called a λ type oxygen sensor, and has a structure in which an elongated plate-shaped ceramic element 2 (synonymous with a detection element) is fixed to a metal shell 3. Then, the front end side detection portion D is mounted so as to be located in the exhaust pipe by the mounting screw portion 3a formed on the outer peripheral surface of the metal shell 3, and the high temperature exhaust gas as the measured gas flowing in the exhaust pipe. Be exposed to. In the present specification, the detection unit D is arranged in the direction of the central axis O of the metal shell 3 (also simply referred to as the axis O).
The description will be made assuming that the protruding side of "is the front side (or the front end side)" and the opposite side is the "rear side (or the rear end side)".

The ceramic element 2 has a rectangular axial cross section, and as shown in FIG. 2 (a), an oxygen concentration battery element 21 formed in a horizontally long plate shape and the oxygen concentration battery element 2 respectively.
Ceramic heater 22 for heating 1 to a predetermined activation temperature
And are configured to be laminated. The oxygen concentration battery element 21 is composed of an oxygen ion conductive solid electrolyte mainly composed of zirconia or the like. On the other hand, the ceramic heater 22 is a known one having a resistance heating element built therein.

In the oxygen concentration battery element 21, the porous electrodes 25 and 26 have electrode lead portions 25a and 26a extending in the longitudinal direction toward the mounting base end side of the oxygen sensor 1.
Are integrated respectively. Of these, the electrode lead portion 25a from the electrode 25 on the side not facing the ceramic heater 22 has its end used as the electrode terminal portion 7.
In the detection part D, the protective layer 2 is formed so as to cover the electrode on one side in the stacking direction, that is, the porous electrode 25 forming the gas detection surface.
4 are provided. The protective layer 24 is mainly made of alumina or the like, has a high thermal shock resistance, and is a porous ceramic layer that allows oxygen molecules to easily pass therethrough.

On the other hand, as shown in FIG. 2C, the electrode lead portion 26a of the electrode 26 on the side opposite to the ceramic heater 22 is provided with a via 26b that crosses the oxygen concentration battery element 21 in the thickness direction, and the element on the opposite side. Electrode terminal portion 7 formed on the surface
Connected with. That is, the oxygen concentration battery element 21
Is the electrode terminal portion 7 of both porous electrodes 25, 26.
It is formed so as to be lined up at the end of the side plate surface. The above-mentioned electrodes, electrode terminal portions and vias are obtained by forming a pattern by screen printing using a paste of metal powder having catalytic activity for oxygen molecule dissociation reaction, such as Pt or Pt alloy, and firing it. It is a thing.

On the other hand, lead portions 23a, 23a for energizing the resistance heating element pattern 23 of the ceramic heater 22.
Also, as shown in FIG. 2D, the ceramic heater 22 is connected to the electrode terminal portions 7, 7 formed at the end of the plate surface on the side not facing the oxygen concentration battery element 21 via the vias 23b, respectively. There is. FIG. 2B shows a cross section HS of the detector D perpendicular to the axis O direction. As shown in the figure, the oxygen concentration battery element 21 and the ceramic heater 22 are bonded to each other via a ceramic layer 27 such as a ZrO ₂ system ceramic or an Al ₂ O ₃ system ceramic.
Then, in the oxygen concentration battery element 21, the porous electrode (oxygen reference side porous electrode) 26 on the bonding side functions as an oxygen reference electrode by the application of a minute pumping current, while the porous electrode 25 on the opposite side is exhausted. It becomes the detection side electrode that comes into contact with the gas, and its surface becomes the gas detection surface. As described above, in the detection unit D, the porous electrode 25 is formed on the surface of the plate-shaped oxygen concentration battery element 21, and the protective layer 24 made of porous ceramic is provided so as to cover the porous electrode 25. ing.
The ceramic heater 2 is provided on the back surface side opposite to the protective layer 24 in the plate thickness direction of the oxygen concentration battery element 21.
Two are adjacent to each other.

Returning to FIG. 1, the ceramic element 2 is inserted into the insertion hole 30 of the insulator 4 arranged inside the metal shell 3, and the detection portion D on the front end side is fixed to the exhaust pipe. It is fixed in the insulator 4 while protruding from the front end.
One end of the insulator 4 communicates with the rear end of the insertion hole 30 in the axial direction, the other end opens to the rear end surface of the insulator 4, and the void portion 31 has an axial cross section larger than that of the insertion hole 30. Are formed. A space between the inner surface of the void 31 and the outer surface of the ceramic element 2 is sealed by a sealing material layer 32 mainly composed of glass (for example, crystallized zinc silica borate glass).

A talc ring 36 and a caulking ring 37 are fitted between the insulator 4 and the metal shell 3 so as to be adjacent to each other in the axial direction, and the outer peripheral portion of the metal shell 3 on the rear end side is caulking ring 37. The insulator 4 and the metal shell 3 are fixed to each other by caulking the insulator 4 side via the.

A ceramic separator 16 and a grommet 15 are fitted inside the rear end of the outer cylinder 18,
Following these, a connector portion 13 is provided further inward. The rear end side of the lead wire 14 penetrates the ceramic separator 16 and extends to the outside. On the other hand, the front end side of the lead wire 14 is electrically connected to each electrode terminal portion 7 of the ceramic element 2 shown in FIG. 2 via the connector portion 13.

The oxygen sensor 1 is fixed to the exhaust pipe of the vehicle at the mounting screw portion 3a. When the detection part D is exposed to exhaust gas, the porous electrode 25 of the oxygen concentration battery element 21
(FIG. 2) comes into contact with the exhaust gas, and an oxygen concentration battery electromotive force corresponding to the oxygen concentration in the exhaust gas is generated in the oxygen concentration battery element 21. This electromotive force is taken out as a sensor output.

At the front end of the metal shell 3, the ceramic element 2
Of the cylindrical protector 6b in a form of covering the protruding portion of the inner protector 6b, that is, the detection portion D, and the axis O on the outer side of the protector 6b.
A cylindrical outer protector 6a, which is also coaxially arranged with respect to, is fixed. Mounting screw part 3a of the metal shell 3
The front end side portion is slightly reduced in diameter to form a small diameter portion 3b. The protectors 6a and 6b have side walls W respectively.
The base end sides of W1 and W3 are fitted to each other in the small diameter portion 3b, and the laser welded portion 65 is formed along the circumferential direction.
Are fixed by forming. Each protector 6
Alignment marks (not shown) on the base end side of a and 6b
Is engraved, the ceramic element 2 and the inner protector 6b
Fitting and welding can be performed while adjusting the angular positional relationship between the outer protector 6a and the outer protector 6a. Since the protector has the double structure as described above, it has an excellent protection function for the detection unit D. The inner and outer protectors 6a and 6b having a double structure form an essential part of the present invention and will be described in detail below.

First, FIG. 3 is an enlarged half sectional view of the outer protector 6a and the inner protector 6b. Outer protector 6a
In the side wall W1 of the above, a gas flow hole 63 for flowing the gas to be detected is formed in a direction intersecting the axis O.
A plurality of gas circulation holes 63 are formed in the circumferential direction. The outer protector 6a is a cylindrical member having a substantially constant diameter, and the inner space G1 is formed by a front end portion W2 forming a cylindrical bottom and a side wall portion W1 formed so as to extend from the peripheral edge of the front end portion W2 to the rear side of the axis O. Has been formed. The front end W2 has an axis O
The front end gas flow hole 62 is formed in such a positional relationship that the center of gravity of the hole substantially coincides with the center of gravity of the hole. The inner protector 6b has a shape in which the side wall portion W3 is reduced in diameter toward the front side, and the front end portion W4 forming the cylinder bottom is also provided with a gas discharge hole in a positional relationship in which the axis O and the center of gravity of the hole are substantially aligned. 61 is formed. In this embodiment, the gas flow hole 62 and the gas discharge hole 61 are formed in a circular shape.

Further, only one gas introduction hole 60 is formed in the side wall W3 of the inner protector 6b. The gas to be detected introduced into the internal space G1 from the gas flow hole 63 of the outer protector 6a is guided to the detection space G2 through the gas introduction hole 60 in a direction intersecting the axis O, and the gas discharge hole 6 is discharged.
Emitted from 1.

FIG. 4 shows a cross section HS perpendicular to the axis O at a position including the detection portion D. The detector D is located near the center of the inner protector 6b so that the protective layer 24 faces the gas introduction hole 60. Here, in the plate thickness direction of the plate-shaped oxygen concentration battery element 21 forming the detection portion D, the side having the protective layer 24 is the front side of the oxygen sensor 1. Also,
As shown in FIG. 1, in the present embodiment, the metal shell 3
The axis O of the ceramic element 2 and the axis O of the ceramic element 2 substantially coincide with each other. Strictly defining the axis of the ceramic element 2, for example, the rod-shaped ceramic element 2
The central axis of the right circular cylinder having the smallest volume inscribed by can be the axis of the ceramic element 2.

As described above, the plate-shaped ceramic element 2 used in this embodiment is weak against thermal shock. Therefore, the protector has a double structure to protect the detection unit D from condensed water, but the protection function (also referred to as water coverage) is dramatically improved by adopting the present embodiment. Specifically: First, in the cross section HS shown in FIG. 4, the electrode 25 of the detection unit D and the protective layer 24 covering the electrode 25 are provided.
The joint boundary line JB is defined. The junction boundary line JB is perpendicular to the plate thickness direction of the oxygen concentration battery element 21. And
When the side wall portion W3 of the inner protector 6b is divided into two parts on an imaginary plane that includes the joint boundary line JB and is parallel to the axis O,
The gas introduction hole 60 is formed only on one side located on the front side. That is, it is preferable that the gas introduction hole 60 be within the angle range indicated by θ ₁ in this cross-sectional view.

In the detection section D, the portion where the protective layer 24 is not formed, specifically, the side surface portion of each layer and the surface where the ceramic heater 22 is formed are inferior in thermal shock resistance. Therefore, if the gas introduction hole 60 of the inner protector 6b is formed only on the front side of the joint boundary line JB, even when condensed water or the like generated on the inner peripheral surface of the outer protector 6a enters the detection space G2. At least, it can be prevented or suppressed that it adheres to the side surface of the detection unit D or the surface on the ceramic heater 22 side. Since the electrode 25 is formed by a technique such as screen printing, the thickness thereof is very small. Therefore, the junction boundary line JB is actually the protective layer 2
It can also be considered that it is almost equal to the junction boundary between the oxygen concentration cell element 4 and the oxygen concentration cell element 21.

Incidentally, the gas introduction hole 60 in the direction of the axis O
Regarding the position of, it is not desirable that there is a hole at a position where the protective layer 24 is not formed. Therefore, when considering a line segment that is perpendicular to the axis O that passes through the rear end of the gas introduction hole, it is preferable that the protective layer 24 is provided further rearward than the line segment. Alternatively, the entire detection surface side of the ceramic element 2 may be covered with the protective layer 24. Further, regarding the position where the cross section HS can be adopted, the axis O
It is an arbitrary position within the range in which the protective layer 24 is formed in the direction.

FIG. 5 is a sectional view similar to FIG. 4, and illustrates a more desirable formation region of the gas introduction hole 60. First, when the gas introduction hole 60 is contained within the angle range indicated by θ ₂ in FIG. 5, even when a water drop or an oil drop enters the detection space G2 from the gas introduction hole 60,
It is very difficult for them to reach not only the surface on the side of the ceramic heater 22 but also the side surface of each layer forming the detection unit D. In particular, in the present embodiment in which the gas introduction holes are provided in a very limited angular range of the inner protector 6b, the gas is generated around the detection portion D in the detection space G2 as compared with the case where the holes are provided in the entire circumferential direction. The swirling flow is also slight. for that reason,
It is also effectively suppressed that the invading mist-like water drops go around to the other side.

The angle range indicated by θ ₂ is shown in FIG.
It is a range included in θ ₁ shown in. Specifically, first, in the above-described cross section HS, the surrounding area WR having the smallest rectangular shape capable of surrounding the detecting portion D including the protective layer 24 is determined. In the present embodiment, the outer shape line of the detection unit D is equal to the surrounding region WR in the cross section HS. Next, the surrounding area W
The side wall W3 of the inner protector 6b is divided into four by two virtual planes that include the diagonal lines HL and HL of R and are parallel to the axis O. Then, of the four side wall parts W3
The gas introduction hole 60 is formed only in the portion directly facing the protective layer 24. If there is a concern that the response speed of the element may decrease, the gas introduction holes 60 may be provided at a plurality of positions within the allowable range, or the gas introduction holes 60 may be adjusted depending on the size of the holes.

As shown in the schematic sectional view of FIG. 6, the ceramic element 2 may be provided with a chamfered portion cf after or before firing in order to enhance mechanical strength and thermal shock resistance. Therefore, if the surrounding region WR is determined as described above, even if the cross-sectional shape of the detection portion D is not rectangular, the formation region of the gas introduction hole 60 can be easily specified.

Next, when the gas sensor 1 is required to have extremely high water content, the gas introducing hole 60 is formed in the inner protector 6b.
A method of forming the will be described. First, FIG. 7 shows a cross-section HS similar to that shown in FIG. First, a pair of parallel reference lines PL and P that are parallel to the plate thickness direction in the detection unit D and have a minimum width that can accommodate the protective layer 24 therebetween.
Determine L. Further, including the parallel reference lines PL, PL,
And the inner protector 6 on two virtual planes parallel to the axis O.
The side wall W3 of b is divided into four. Then, the gas introduction hole 60 may be formed so that the center of gravity G of the side wall portion W3 divided into four parts is located at a portion directly facing the protective layer 24. That is, the center of gravity G of the hole is adjusted within the range of the angle θ ₃ shown in FIG. 7. In this way, even if compared with the form illustrated in FIGS. 4 and 5,
Higher wettability can be imparted to the inner protector 6b. This is because it is considered that the position at which the gas to be detected most passes through is the center of gravity G.

It should be noted that a configuration may be adopted in which most of the gas introduction holes 60 (for example, more than half the area of the holes on the outer peripheral surface of the protector) are set within the range of the angle θ ₃ . Alternatively, the gas introduction hole 60 is provided within the range of the angle θ _3.
It is more desirable that the gas introduction hole 60 directly faces the protective layer 24 if almost all of the above are accommodated.

Next, the positional relationship between the holes formed in the side wall portions W1 and W3 of the inner and outer protectors 6a and 6b will be described. As shown in FIG. 4, the side wall W1 of the outer protector 6a
The gas passage hole 63 formed in the above is adjusted so as not to overlap the gas introduction hole 60 formed in the side wall portion W3 of the inner protector 6b in the circumferential direction. If you do this,
Even if the gas to be detected introduced through the gas flow hole 63 of the outer protector 6a contains water droplets or the like, it is prevented from directly entering the detection space G2 of the inner protector 6b.

The positional relationship of the holes will be specifically described. Figure 10
[FIG. 4] is an enlarged cross-sectional view in a direction perpendicular to the axis O of the protectors 6a and 6b inside and outside. First, the reference line K that passes through the center of gravity G of the gas flow hole 63 formed in the side wall portion W1 of the outer protector 6a and intersects the axis O at right angles is determined. On the other hand, the opening edge of the gas flow hole 63 on the side closer to the inner protector 6b is defined as the outline FP of the gas flow hole 63. Then, keeping the distance from the reference line K constant, the outline F
P is projected on the side wall W3 of the inner protector 6b. It is preferable that the projection line FP ′ is adjusted so as not to overlap the gas introduction hole 60 formed in the sidewall W3 of the inner protector 6b.

In addition to the circumferential direction, as shown in the schematic view of FIG. 8A, the gas inlet 60 of the inner protector and the gas flow hole 63 of the outer protector are adjusted so as not to overlap in the axis O direction. It is still good if it is done. The fact that the oxygen sensor 1 does not overlap in the direction of the axis O means that the projection line of the gas flow hole 63 and the projection line of the gas introduction hole 60 do not overlap when the oxygen sensor 1 is perspectively projected on a plane parallel to the axis O. . Some positions of the gas introduction hole 60 in the direction of the axis O can be illustrated in the schematic view of FIG. 8B, for example. When all the holes are located on the rear side of the front end of the ceramic element 2, that is, in the region L1. When the ceramic element 2 and a part of the hole overlap (region L2). In the case where all of the holes are located on the front side of the front end of the ceramic element 2, that is, in the region L3. In the order of high wetness, the order is ,, but the responsiveness is opposite. Therefore, various adjustments may be made according to the required performance.

Further, as shown in FIG. 10, the gas flow hole 6
For 3, the shape in which the cross-sectional area of the hole is reduced as it goes to the inner space G1 side can be adopted. With this configuration, the gas to be detected introduced from the outside is easy to proceed straight while maintaining its direction. In the case of FIG. 10, the gas to be detected introduced through the gas flow hole 63 once comes into contact with the side wall W3 of the inner protector 6b and diffuses. This form can also be adopted for the gas introduction hole 60 formed in the inner protector 6b.

The "center of gravity G of the hole" referred to in this specification is determined as follows. That is, as shown in FIG. 10, this occurs when a space S formed by closing the open end of the hole with a virtual surface (not necessarily a flat surface) having the smallest area is filled with a substance of uniform density. The center of mass is defined as "center of gravity G of hole".

Next, FIG. 9 is a schematic diagram for explaining the relationship between the flow of the gas to be detected and the holes formed in the protectors 6a and 6b. It is preferable that the gas flow holes 63 be formed at least at three or more locations on the side wall W1 of the outer protector 6a at equal angular intervals in the circumferential direction. In the form shown, they are equiangularly spaced at 120 °. If you do this,
As shown in (a) and (b), even when the mounting angle of the oxygen sensor 1 to the exhaust pipe or the like is reversed by 180 ° and the hole position is not fixed with respect to the flow EG of the gas to be detected, the gas to be detected is not detected. Are introduced into the internal space G1 of the outer protector 6a along the gas flow. And gradually the inner protector 6
It also diffuses into the detection space G2 in b.

[0036]

[Experimental Example] In order to confirm the effectiveness of the present invention, a ceramic element 2 having the structure shown in FIG. 2 is produced, and a small amount of water is dropped on the ceramic element 2 with a micropipette while heating the ceramic heater 22. I did a water test. As schematically shown in FIG. 11, the protective layer (front surface), the side surface, and the heater surface (rear surface) were set as water dropping positions. The amount of dripping water at which cracks were generated in each portion was investigated and plotted against the heat generation temperature on the heater surface. The generation of cracks is confirmed visually. FIG. 12 is a graph showing the results. In the graph, as schematically shown in FIG. 13, a region that is always larger than the pseudo envelope f (α) formed by connecting the measurement points can be seen as a crack generation region. The narrower the cracked area, the higher the wettability.

From the results of the experiment, it can be seen that the front portion on which the protective layer is formed shows much higher wettability in the low temperature region than the side portion and the heater portion. That is, even if some water adheres to the protective layer, the ceramic element 2 is less likely to be damaged. In the gas sensor 1 of the present invention, the gas introduction hole 60 is formed at a position facing the protective layer as much as possible, so that the side surface portion and the heater portion can be protected from adhesion of water. That is, even in an environment where a large amount of condensed water is generated, the ceramic element 2 is unlikely to be cracked. In addition,
Even in the protective layer, the water content decreases as the heat generation temperature of the heater surface rises, but a large amount of water is almost immediately after the engine is started. Therefore, considering that the amount of water that has been exposed to water after the heater has been sufficiently heated is small, the decrease in water coverage of the protective layer in the high temperature range is not a serious problem.

It is needless to say that the present invention is not limited to the above embodiments and can be implemented in various modes without departing from the scope of the invention. Also, the attached drawings are
Note that it is a schematic or conceptual one for understanding.

[Brief description of drawings]

FIG. 1 is an overall view showing a longitudinal section of an oxygen sensor showing an embodiment of a gas sensor of the present invention.

FIG. 2 is a structural explanatory view of a ceramic element.

FIG. 3 is an enlarged half cross-sectional view of an outer protector and an inner protector.

FIG. 4 is a cross-sectional view perpendicular to the axis at a position including a detection unit.

FIG. 5 is a cross-sectional view showing a formation range of a gas introduction hole formed in an inner protector, the cross section being perpendicular to an axis line at a position including a detection portion.

FIG. 6 is a schematic sectional view of a ceramic element.

7 is a cross-sectional view following FIG.

FIG. 8 is a schematic diagram illustrating a positional relationship between a gas flow hole and a gas introduction hole in an axial direction.

FIG. 9 is a schematic diagram illustrating the relationship between the flow of a gas to be detected and the holes formed in the protector.

FIG. 10 is an enlarged sectional view perpendicular to the axis of the protector.

FIG. 11 is a schematic diagram illustrating a method of a water test.

FIG. 12 is a graph in which the test results are plotted.

FIG. 13 is a schematic diagram illustrating how to read a graph.

[Explanation of symbols] 1 gas sensor 2 Ceramic element (detection element) 6a protector 6b outer protector 21 Solid electrolyte body (oxygen concentration battery element) 24 Protective layer 25 electrodes 60 gas inlet 63 Gas flow hole Side wall of W1 outer protector Side wall of protector inside W3 JB junction boundary G2 detection space HS cross section D detector O axis WR surrounding area HL diagonal PL parallel reference line G center of gravity K reference line FP outline FP 'projection line

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Keiichi Noda             14-18 Takatsuji-cho, Mizuho-ku, Nagoya City, Aichi Prefecture             Inside this special ceramics company (72) Inventor Keisuke Makino             14-18 Takatsuji-cho, Mizuho-ku, Nagoya City, Aichi Prefecture             Inside this special ceramics company

Claims (5)

[Claims] 1. A detection part (D) formed on the front end side of the detection element (2) in the direction of the axis (O), a cylindrical inner protector (6b) provided so as to cover the detection part (D), and the inner protector. In the gas sensor (1) provided with a tubular outer protector (6a) which is also arranged outside (6b), the detection unit (D) has electrodes () on the surface of the plate-shaped solid electrolyte body (21). 25) is formed, a protective layer (24) is provided so as to cover the electrode (25), and a ceramic heater (22) is adjacent to the back surface side of the outer protector (6a). In (W1), there are gas circulation holes (6) for circulating the gas to be detected in and out of itself.
3) is formed, and a gas introduction hole (60) for introducing the gas to be detected into the detection space (G2) inside itself is formed in the side wall portion (W3) of the inner protector (6b). The side with the protective layer (24) in the plate thickness direction of the solid electrolyte body (21) is defined as the front side of the gas sensor (1), and further includes the detection unit (D) in the axis (O) direction. In the cross section (HS) perpendicular to, the joint boundary line (JB) perpendicular to the plate thickness direction between the electrode (25) and the protective layer (24) covering the electrode (25) is defined, and the joint boundary line (JB) is defined. And the side wall portion (W3) of the inner protector (6b) is divided into two parts on an imaginary plane parallel to the axis (O),
The gas inlet hole (6
Gas sensor (1) characterized in that 0) is formed. 2. In the cross section (HS), a minimum rectangular enclosing region (WR) that can enclose the detection part (D) including the protective layer (24) is defined, and the enclosing region (W).
When the side wall portion (W3) of the inner protector (6b) is divided into four by two virtual planes including the diagonal line (HL, HL) of R) and parallel to the axis line (O), the gas introduction hole ( The gas sensor (1) according to claim 1, wherein the portion (60) is formed only on a portion of the divided side wall portion (W3) that faces the protective layer (24). 3. A parallel reference line (PL, PL) having a minimum width that is parallel to the plate thickness direction and that can accommodate the protective layer (24) in the cross section (HS) is defined, and further, When the side wall portion (W3) of the inner protector (6b) is divided into four by two virtual planes including the parallel reference lines (PL, PL) and parallel to the axis line (O), the gas introduction hole ( The gas sensor (1) according to claim 1 or 2, wherein 60) is formed so that its center of gravity is located at a portion of the divided side wall portion (W3) directly facing the protective layer (24). . 4. A side wall portion (W) of the outer protector (6a).
The gas sensor (1) according to any one of claims 1 to 3, wherein the gas flow holes (63) are formed in at least three locations in 1) at equal angular intervals in the circumferential direction. 5. A side wall portion (W) of the outer protector (6a).
Center of gravity (G) of the gas flow hole (63) formed in 1)
While defining a reference line (K) that passes through the axis and intersects perpendicularly with the axis (O), the opening edge of the gas flow hole (63) is used as the outer shape line (FP) of the gas flow hole (63). , The contour line (FP) is kept constant at a distance from the reference line (K), and a side wall portion (W3) of the inner protector (6b).
5. The projection line (FP ') is adjusted so as not to overlap the gas introduction hole (60) formed in the side wall portion (W3) of the inner protector (6b) when projected onto the surface. The gas sensor (1) according to any one of claims.