JP2012112739A - Gas sensor, gas sensor manufacturing method, and gas sensor unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor, a gas sensor manufacturing method, and a gas sensor unit, capable of suppressing or mitigating thermal shock due to water covering of a ceramic enclosure.SOLUTION: A gas sensor 21 comprises: a bottom cylindrical gas detection element 22 extending in an axial direction o and having a tip side exposed to a gas to be measured; a main body metal fitting 25 surrounding the periphery of the gas detection element; a cylindrical ceramic enclosure 23 made of a nonconductive ceramic, surrounding the periphery of the rear end side of the gas detection element, and held by the main body metal fitting in a form of protruding this rear end side more than the rear end of the main body metal fitting; and a terminal member 24 connected with an inner electrode 29 formed in the inner peripheral surface of the gas detection element, outputting an output signal from the gas detection element to the outside, and held in the cylinder of the ceramic enclosure, in which a glaze layer 231 is formed at least on the outer surface of the ceramic enclosure and no needle crystal having a length of 50 μm or more is present in the surface of the glaze layer.

Description

  The present invention includes a gas sensor having a gas detection element and holding a terminal member for outputting an output signal from the gas detection element to the outside inside the ceramic enclosure, a method for manufacturing the gas sensor, and a sensor cap attached to the gas sensor The present invention relates to a gas sensor unit.

  Conventionally, various gas sensors having gas detection elements have been proposed. These gas sensors include, for example, a gas detection element made of a solid electrolyte body having oxygen ion conductivity, and are attached to an object to be attached such as an exhaust pipe or an engine head of an internal combustion engine, and a specific gas in the exhaust gas. One that detects the concentration of oxygen (for example, oxygen). In some gas sensors, a sensor cap is detachably placed at the rear end of the gas sensor in order to transmit the output from the gas sensor to the outside, thereby constituting a gas sensor unit as a whole. (For example, refer to Patent Document 1).

In the gas sensor unit described in Patent Literature 1, the gas sensor surrounds the periphery of the gas detection element with a metal metal shell, surrounds the rear end side of the gas detection element with a ceramic enclosure, and further outputs an output signal from the gas detection element. The terminal member that outputs to the outside is held inside the ceramic enclosure.
On the other hand, the sensor cap includes a cap terminal connected to the terminal member and a rubber-made terminal enclosure. The terminal enclosure holds the cap terminal, and the rear end side of the ceramic enclosure is placed in its insertion hole. It can be accommodated.

  By the way, since the metal shell becomes high temperature due to the heat of the exhaust, the rubber sensor cap (terminal surrounding portion) also becomes high temperature (for example, 200 ° C. or more) due to this heat propagation or radiation heat, and the sensor cap may be deteriorated. There is. Therefore, in order to reduce such heat damage, the front end of the sensor cap is spaced apart from the rear end of the metallic shell in the axial direction, and a part of the enclosure is exposed from this gap (hereinafter referred to as an exposed portion). Furthermore, if the exposed portion of the ceramic enclosure is exposed to water or the like from the outside, the ceramic enclosure that is vulnerable to thermal shock may be damaged. Therefore, in the technique described in Patent Document 1, the ceramic enclosure is exposed. A glaze layer is formed on the part. In this case, when the exposed portion of the ceramic enclosure is flooded, the glaze layer is first flooded, but the glaze layer alleviates the thermal shock, so that the impact is hardly transmitted to the exposed portion of the ceramic enclosure.

JP 2005-201888 A

However, when the glaze layer is formed on the ceramic enclosure by heat treatment after the glaze is applied to the ceramic enclosure, depending on the firing temperature, the formation of the glaze layer may be insufficient, or acicular crystals may form on the surface of the glaze layer. It has been found that the glaze layer is formed in an exposed form, thereby reducing the denseness of the glaze layer. When the denseness of the glaze layer is lowered, it becomes difficult to mitigate the thermal shock of the exposed portion of the ceramic enclosure, and the ceramic enclosure may be damaged by water.
Therefore, an object of the present invention is to provide a gas sensor and a gas sensor unit in which a glaze layer is densely formed on the surface of a ceramic enclosure so that thermal shock due to moisture on the ceramic enclosure can be suppressed or alleviated.

In order to solve the above problems, a gas sensor of the present invention includes a bottomed cylindrical gas detection element that extends in the axial direction and is exposed to a gas to be measured, and a metal shell that surrounds the gas detection element. In a cylindrical shape made of insulating ceramic, surrounding the periphery of the rear end side of the gas detection element, and a ceramic enclosure held by the metal shell in a form in which the rear end side of the gas detection element protrudes from the rear end of the metal shell,
A terminal member connected to an inner electrode formed on an inner peripheral surface of the gas detection element, outputting an output signal from the gas detection element to the outside, and held in a cylinder of the ceramic enclosure; A glaze layer is formed on at least the outer surface of the enclosure, and no acicular crystals having a length of 50 μm or more are present on the surface of the glaze layer.
According to such a gas sensor, the glaze layer is formed in a form in which the acicular crystals are not exposed on the surface of the glaze layer, so that the glaze layer becomes dense and the thermal shock of the ceramic enclosure due to moisture can be reduced. Can do.
In addition, it has been found that acicular crystals having a length of 50 μm or more affect the denseness of the glaze layer, and the acicular crystals have an aspect ratio (major axis / minor axis) of 2 or more. Refers to the crystal.

The gas sensor manufacturing method of the present invention includes a bottomed cylindrical gas detection element that extends in the axial direction and whose tip side is exposed to a gas to be measured, a metal shell that surrounds the periphery of the gas detection element, and an insulating ceramic. A ceramic enclosure that surrounds the rear end side of the gas detection element and is held by the metal shell in a form in which the rear end side of the gas detection element protrudes from the rear end of the metal shell, and the gas detection element A gas sensor manufacturing method comprising: a terminal member connected to an inner electrode formed on an inner peripheral surface of the gas sensor; and outputting an output signal from the gas detection element to the outside, and a terminal member held in a cylinder of the ceramic enclosure, After applying a glaze to at least the outer surface of the ceramic enclosure, heat treatment is performed at a temperature of 1250 ° C. or more and 1300 ° C. or less to form a glaze layer on the ceramic enclosure.
When the ceramic enclosure is formed in this manner, the formation of a needle crystal having a length of 50 μm or more on the surface of the glaze layer is suppressed, the glaze layer becomes dense, and the thermal shock of the ceramic enclosure due to moisture is reduced. can do. When the heat treatment temperature exceeds 1300 ° C., needle-like crystals having a length of 50 μm or more are formed on the surface of the glaze layer, and the denseness of the glaze layer may be reduced. On the other hand, if the heat treatment temperature is less than 1250 ° C., the desired glaze layer is not formed, and the glaze layer surface becomes uneven, which may reduce the denseness of the glaze layer 231.

The gas sensor unit according to the present invention includes the gas sensor, a cap terminal that is connected to the terminal member of the gas sensor and transmits the output signal to an external device, and an insertion that surrounds the cap terminal and a rear end side of the ceramic enclosure. And a gas sensor cap having a terminal surrounding portion that holds the cap terminal and is made of an elastic member having a hole.
The gas sensor of the present invention can also be applied to such a gas sensor unit.

  According to the present invention, it is possible to obtain a gas sensor, a gas sensor manufacturing method, and a gas sensor unit, in which a glaze layer is densely formed on the surface of the ceramic enclosure, and thermal shock due to moisture on the ceramic enclosure can be suppressed or alleviated. .

It is sectional drawing which follows the axial direction of the gas sensor concerning embodiment of this invention. It is sectional drawing which shows a gas sensor unit. It is sectional drawing which follows the axial direction of a sensor cap. It is explanatory drawing of a cap terminal, (a) is a front view, (b) is a bottom view. It is a figure which shows the test device which submerges a gas sensor unit. It is a metal-microscope image of the ceramic enclosure (glaze layer) surface of Example 3. 2 is a metallographic microscope image of the surface of a ceramic enclosure (glaze layer) of Comparative Example 1.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view along the direction of the axis O of a gas sensor 21 according to an embodiment of the present invention. FIG. 2 is an explanatory view showing the gas sensor unit 600 in which the sensor cap 700 is attached to the gas sensor 21, and the state when the gas sensor unit 600 is used, and is a cross-sectional view along the axis O direction.
As can be understood from FIG. 2, the gas sensor unit 600 includes the gas sensor 21 and a sensor cap 700 disposed on the rear end side (upward in FIG. 2) of the gas sensor 21 in the axis O direction. The gas sensor unit 600 is an oxygen sensor that is fastened to a vehicle exhaust pipe (attachment target body) in a form in which a tip portion of the gas sensor 21 protrudes into the exhaust pipe, and measures the oxygen concentration in the exhaust gas. Note that the front end of the sensor cap 700 is spaced apart from the rear end of the metal shell 25 in the axial direction, and the ceramic enclosure 23 is exposed from the gap therebetween.

  As shown in FIG. 1, the gas sensor 21 includes a gas detection element 22, a ceramic enclosure 23, a terminal member 24, and a metal shell 25. In the following description, in the direction along the axis O, the side on which the sensor cap is attached is referred to as the rear end side, and the opposite side is referred to as the front end side.

The metal shell 25 is made of SUS430 and is formed in a cylindrical shape. The metal shell 25 is an inner periphery receiving portion 25a for supporting a flange-like protruding portion 22b of the gas detection element 22 described later, and has a taper that decreases in diameter toward the distal end side (downward in FIG. 1). The inner periphery receiving portion 25a having a shape is provided around the inner peripheral surface so as to protrude radially inward. Further, a screw portion 25b for attaching the gas sensor 21 to the exhaust pipe is formed outside the metal shell 25, and a screw portion 25b is provided on the rear end side (upward in FIG. 1) of the screw portion 25b. A collar portion (hexagonal portion) 25c that engages with a mounting tool for screwing the tube into the exhaust pipe is provided. The flange portion 25 c protrudes radially outward from the other outer surface of the metal shell 25. An annular gasket 33 for sealing when the gas sensor 21 is attached to the exhaust pipe is fitted to the tip-facing surface of the flange portion 25c.
A protector 26 is attached to the front end side of the metal shell 25 so as to cover a front end portion 22a of a gas detection element 22 described later. The protector 26 is a metal, cylindrical bottomed cylindrical body, and has a plurality of vent holes 26 a for introducing exhaust gas in the exhaust pipe into the gas sensor 21.

The gas detection element 22 is made of a solid electrolyte having oxygen ion conductivity, and has a bottomed shape with a closed end 22a and a cylindrical shape extending in the direction of the axis O. On the outer periphery of the gas detection element 21, a hook-like protrusion 22b protruding outward in the radial direction is provided, and the tip side surface of the protrusion 22b and the surface of the inner periphery receiving part 25a of the metal shell 25 are provided. The gas detection element 22 is disposed in the metal shell 25 with a metal packing 27 interposed therebetween. As the solid electrolyte constituting the gas detection element 22, for example, ZrO _{2 in} which Y ₂ O ₃ or CaO is dissolved is representative, but oxidation of other alkaline earth metals or rare earth metals is typical. it may be used a solid solution of the goods and ZrO _2. Furthermore, HfO ₂ may be contained therein.

An outer electrode 28 is formed on the outer peripheral surface of the distal end portion 22 a of the gas detection element 22. The outer electrode 28 is made of porous Pt or Pt alloy. The outer electrode 28 is provided up to the tip side surface of the protruding portion 22 b and is electrically connected to the metal shell 25 via a metal packing 27. Therefore, the potential of the outer electrode 28 can be taken out from the metal shell 25.
On the other hand, an inner electrode 29 is formed on the inner peripheral surface of the gas detection element 120. This inner electrode 29 is also made of Pt or a Pt alloy formed porous.

The ceramic enclosure 23 is made of an insulating ceramic (specifically, alumina) and has a cylindrical shape. This ceramic enclosure 23 is a ceramic formed from talc in such a manner that the thickened tip side portion 23a surrounds the portion of the gas detection element 22 on the rear end side of the protruding portion 22b. Along with the powder 30, it is held so as to be interposed between the gas detection element 22 and the metal shell 25.
A glaze layer 231 is formed on the outer surface of the ceramic enclosure 23. This glaze layer 231 is formed smoothly as shown in FIG. 6, and there is no needle crystal having a length of 50 μm or more. Here, the form of the surface of the glaze layer 231 can be confirmed by, for example, an image of a metal microscope or a scanning electron microscope having a magnification of about 200 times. As will be described later, when the firing temperature for forming the glaze layer 231 and the ceramic enclosure 23 exceeds 1300 ° C., needle-like crystals having a length of 50 μm or more are formed on the surface of the glaze layer 231 and the surface of the glaze layer 231 is rough. Become. When the surface of the glaze layer 231 becomes rough in this way, the denseness is lost, and water penetrates from the glaze layer 231 into the ceramic enclosure 23. Therefore, it is difficult to mitigate the thermal shock of the ceramic enclosure 23 due to water. Become. Therefore, by making needle-shaped crystals having a length of 50 μm or more not exist on the surface of the glaze layer 231, the glaze layer 231 is made dense and the thermal shock of the ceramic enclosure 23 due to moisture is reduced.
In addition, when the wet region (exposed portion) of the ceramic enclosure 23 is known in advance in relation to the mounting position of the sensor cap 700, the glaze layer 231 may be formed only on the exposed portion.

The glaze layer 231 described above can be formed by applying a glaze to the fired ceramic enclosure 23 and then performing a heat treatment at a temperature of 1250 ° C. or higher and 1300 ° C. or lower. Note that if the firing temperature is lower than 1250 ° C., the glaze layer 231 is not sufficiently formed, the surface of the glaze layer 231 becomes uneven, and the glaze layer 231 loses its denseness.
The glaze used for the glaze layer 231 is also called an upper glaze, and is a glassy material applied to the surface of the ceramic enclosure 23 in order to increase the mechanical strength of the ceramic enclosure 23. Specifically, the glaze is borosilicate glass or alkali borosilicate glass.
Although the thickness of the glaze layer 231 is not specifically limited as long as baking is possible, For example, it can be set as about 5-10 micrometers. Moreover, it is preferable that the surface roughness Ra of the glaze layer 231 is 0.4 μm or less because a desired glaze layer 231 is formed.

  The terminal member 24 is made of, for example, Inconel (trade name of Inconel, UK), and has a cylindrical shape, and includes an output side terminal portion 24a, an element side terminal portion 24b, and a terminal connection portion 24c that couples both. Among these, the output-side terminal portion 24a has a cylindrical shape having a substantially C-shaped cross section perpendicular to the axis O. The output side terminal portion 24a moves a sensor connecting portion 751a (see FIG. 3) of a cap terminal 751 described later relative to a direction along the axis O (vertical direction in FIGS. It is configured to elastically expand its diameter when inserted. Further, convex portions 241a protruding radially inward are formed at four positions in the circumferential direction on the rear end side (upward in FIG. 1) of the output side terminal portion 24a.

  Further, in the output side terminal portion 24a, a part of the output side terminal portion 24a is punched out and bent radially inward at three positions in the circumferential direction on the tip side (downward in FIG. 1) from the convex portion 241a. An inner bent portion 242a and an outer bent portion 243a bent outward in the radial direction are formed. Among these, as will be described later, the inner bent portion 242a is elastically radially outward when the insertion portion 751c (see FIG. 4) of the cap terminal 751 is inserted and connected to the inner side of the output side terminal portion 24a. It is bent so that when the insertion portion 751c is inserted to a predetermined position, the bending returns and a click feeling is generated. Further, as shown in FIG. 1, the outer bent portion 243 a comes into contact with the tip surface (step surface) of the step portion 23 b of the ceramic enclosure 23 when the terminal member 24 is assembled to the gas sensor 21, and outputs It plays the role of preventing the side terminal portion 24a (terminal member 24) from coming off.

  On the other hand, among the terminal members 24, the element-side terminal portion 24 b also has a cylindrical shape whose cross section perpendicular to the axis O is substantially C-shaped. As shown in FIG. 1, the element-side terminal portion 24 b is inserted into the gas detection element 22 while being elastically reduced in diameter, and is electrically connected to the inner electrode 29. Therefore, in the gas sensor 21 of the present embodiment, the element side terminal portion 24b is electrically connected while pressing the inner electrode 29 from the inner side toward the outer side in the radial direction.

  Such a terminal member 24 is formed by integral molding by pressing using a single metal plate having a predetermined shape. For this reason, it is easy to form and low cost. Further, in the terminal member 24 of the present embodiment, the metal plate is bent, and the output-side terminal portion 24a and the element-side terminal portion 24b located on the tip side in the axis O direction (downward in FIG. 1) are cylindrically formed. Since it is molded, the reference gas (outside air) taken into the sensor cap 700 can be introduced to the inside (inner electrode 29) of the gas detection element 22.

  Such a gas sensor 21 is manufactured as follows. First, as shown in FIG. 1, the metal shell 25 and the protector 26 are integrated. Next, the gas detection element 22 provided with the outer electrode 28 and the inner electrode 29 is inserted into the metal shell 25 together with the packing 27. Next, the ring packing 31 is disposed on the rear end side of the protruding portion 22 b of the gas detection element 22, and a predetermined amount of ceramic powder 30 is filled in the gap portion between the metal shell 25 and the gas detection element 22. Next, the ceramic enclosure 23 is inserted so that the distal end portion 23 a is interposed between the gas detection element 22 and the metal shell 25, and is brought into contact with the ceramic powder 30. Next, the ceramic enclosure 23 is pressurized toward the distal end side, and under the pressurized state, a caulking ring 32 is interposed between the caulking portion 25d of the metal shell 25 and the ceramic enclosure 23, and the caulking portion. The above components are fixed together by caulking 25d.

Finally, the terminal member 24 is inserted inside the ceramic enclosure 23 and the gas detection element 22. Specifically, the element side terminal portion 24 b of the terminal member 24 is inserted into the gas detection element 22 while being elastically reduced in diameter, and is electrically connected to the inner electrode 29. At the same time, the output side terminal portion 24a is pushed to the tip side, and the stopper portion 244a formed in a petal shape perpendicular to the axis O and radially outward from the rear end of the output side terminal portion 24a is surrounded by a ceramic. The body 23 is brought into contact with the rear end surface. In this way, the output side terminal portion 24 a is arranged inside the ceramic enclosure 23.
The output side terminal portion 24a is pushed in until the stop portion 244a contacts the rear end surface of the ceramic enclosure 23, whereby the outer bent portion 243a bent inward in the radial direction is released and returned, and the ceramic enclosure 23 is returned. Since the front end surface (step surface) of the step portion 23b is engaged, the terminal member 24 can be prevented from coming off. In this way, the gas sensor 100 is completed.

  Next, the sensor cap 700 will be described with reference to the drawings. FIG. 3 is a partially cutaway sectional view of the sensor cap 700. The sensor cap 700 includes a cap terminal 751, a covering member 752 that covers and holds the cap terminal 751, a lead wire 753, and a filter member 754.

  The cap terminal 751 (see FIGS. 3 and 4) is made of, for example, stainless steel (SUS310S or the like), and is formed by forming a plate material into a double substantially cylindrical shape by drawing or the like. Further, the cap terminal 751 has a concentric annular plate-like annular portion 751a with respect to the axis O, and a grip that protrudes to one side (downward in FIG. 4A) along the axis O, continuing to the outer peripheral edge of the annular portion 751a. Part 751b, and cylindrical insertion part 751c which continues to the inner periphery of annular part 751a and protrudes on the same side as grip part 751b. The annular portion 751a, the grip portion 751b, and the insertion portion 751c are integrally molded with each other.

Among these, as shown in FIG. 4, the gripping portion 751b is connected to the outer peripheral edge of the annular portion 751a and protrudes in a C-shape, and slits SL1, SL2, SL3, SL4 from the base end portion 751ba. , And a divided gripping portion 751bb that is divided into five by SL5 and extends. The slits SL1, SL2, and SL3 have a shape extending in the direction of the axis O.
Each of the above-described divided gripping portions 751bb is formed with a protruding portion 751bc that protrudes inward. Specifically, the five protrusions 751bc are arranged in the circumferential direction at an angle of 72 degrees from each other.
As will be described later, five protrusions 751bc are brought into contact with the outer peripheral surface 23c (see FIG. 1) of the ceramic enclosure 23 of the gas sensor 21, respectively, and the gripping portion 751b of the cap terminal 751 serves as the rear end portion of the ceramic enclosure 23. Fit in this part so that it surrounds. In this case (see FIG. 1), the five divided grip portions 751bb are elastically bent outward in the radial direction due to the presence of the divided slits SL1, SL2, SL3, SL4, and SL5. Then, the cap terminal 751 elastically holds the ceramic enclosure 23 by this reaction force.

  On the other hand, as described above, the insertion portion 751c has a cylindrical shape with the axis O as the center, and has a rigidity that prevents deformation such as a reduced diameter and an increased diameter. Therefore, as will be described later, when the gas sensor 21 is inserted into the output side terminal portion 24a and brought into contact with the output side terminal portion 24a, the output side terminal portion 24a can be expanded without deforming itself. The insertion portion 751c is a cylindrical portion having a relatively large diameter from the annular portion 751a side, and a conductive portion 751ca that is relatively long in the direction of the axis O, a small diameter portion 751cb that is smaller in diameter than the conductive portion 751ca, and a small diameter portion 751cb. The insertion tip portion 751cc having a larger diameter is provided in this order.

When the holding portion 751b of the cap terminal 751 is fitted into the ceramic enclosure 23 of the gas sensor 21 (see FIG. 2), the insertion portion 751c is inside the ceramic enclosure 23 and the output side terminal portion 24a of the terminal member 24. Inserted inside. At this time, the conducting portion 751ca contacts the convex portion 241a of the output side terminal portion 24a and is electrically connected to the output side terminal portion 24a. Further, an inner side bent portion 242a of the output side terminal portion 24a is located on the outer side in the radial direction of the small diameter portion 751cb, and when the cap terminal 751 is detached from the terminal member 24, the inner side bent portion 242a is inserted. The portion 751cc is engaged so that it cannot be easily removed. Further, when the insertion portion 751c of the cap terminal 751 is completely inserted into the output-side terminal portion 24a of the terminal member 24, the inner bent portion 242a is released from the state in contact with the insertion tip portion 751cc, and a click feeling is generated. .
As shown in FIG. 1, the annular portion 751 a is an output side terminal portion located on the rear end surface of the ceramic enclosure 23 in a state where the insertion portion 751 ca is inserted into the output side terminal portion 24 a of the terminal member 24. By abutting against the stopper 244a of 24a, the insertion portion 751c of the cap terminal 751 is further prevented from being inserted into the distal end side.

  The covering member 752 is formed into a hollow shape using an insulating fluorine-based rubber, and constitutes a cap terminal accommodating space SPS that accommodates the cap terminal 751. Then, the surface of the covering member 752 is subjected to texturing. The covering member 752 includes a terminal surrounding portion 752a having an insertion hole 752aa surrounding the cap terminal 751 and the rear end side of the ceramic enclosure 23 at the time of the gas sensor unit 600 (see FIG. 2), and from the rear end side of the terminal surrounding portion 752a. A filter surrounding portion 752b that surrounds the periphery of the filter member 754 that is provided so as to protrude radially and closes the communication hole 752ba, and is provided so as to protrude radially from the rear end side of the terminal surrounding portion 752a. A lead wire surrounding portion 752c surrounding the lead wire 753.

  On the other hand, the rear end side (upward in the drawing) of the terminal surrounding portion 752a is located around the grip portion 751b of the cap terminal 751, and the grip portion 751b and the terminal surrounding portion 752a are in contact with each other. On the other hand, on the distal end side (downward in the drawing) of the terminal surrounding portion 752a with respect to the gripping portion 751b, there is a rib 752ab dimensioned to be in close contact with the outer peripheral surface 23c (see FIG. 1) of the ceramic surrounding body 23 of the gas sensor 21. . Two ribs 752ab are provided in the direction of the axis O. The rib 752ab has a rear end side (upward in the drawing) engaged with the tip of the grip portion 751b of the cap terminal 751. The rib 752ab supports the cap terminal 751 in the terminal surrounding portion 752a. is doing.

  Next, the filter surrounding portion 752b will be described (see FIG. 3). The filter surrounding portion 752b surrounds the periphery of the filter member 754 disposed so as to close the communication hole 752ba. Specifically, the filter member 754 is made of PTFE having a continuous porous structure in which fine pores are continuous, and includes a cylindrical main body 754a and a smoothing processing unit 754b surrounding the main body 754a in an annular shape. This is a filter member 754.

  Further, an annular projecting portion 752bb projecting inward is provided in the communication hole 752ba of the filter surrounding portion 752b, and the projecting portion 752bb is brought into close contact with the outer peripheral surface of the filter member 754 to hold the filter member 754. .

  Next, the lead wire surrounding portion 752c will be described (see FIG. 3). The lead wire surrounding portion 752c surrounds the lead wire 753 and is disposed on the opposite side of the filter surrounding portion 752b with the cap terminal 751 interposed therebetween. The lead wire surrounding portion 752c has a lead wire communication hole 752ca that allows the lead wire 753 to communicate therewith.

  The lead wire 753 has a coating material in addition to the core wire. The leading end side of the lead wire 753 is inserted into the insertion portion 751c of the cap terminal 751, and is crimped by the crimping portion 755a of the lead wire fixing member 755 inside the connection portion 751c.

The lead wire fixing member 755 has a substantially cylindrical shape, and includes a fitting portion 755c that fits into the inner wall of the insertion portion 751c of the cap terminal 751 in addition to the crimping portion 755a. Note that an output signal from the inner electrode 29 of the gas detection element 22 of the gas sensor 21 is transmitted to an external device (for example, an engine control unit (ECU)) through the lead wire 753 by the crimping portion 755a and the fitting portion 755c. It becomes possible. Further, it further includes a substantially C-shaped covering material fixing portion 755b that is positioned between the crimped portion 755a and the fitting portion 755c and fixes the lead wire (covering material). In addition, a joint portion 755d is formed on the rear end side of the fitting portion 755c so as to protrude radially outward and is joined to the annular portion 751a of the cap terminal 751. The joint portion 755d and the annular portion 751a of the cap terminal 751 are joined by welding or the like.
As a result, as shown in FIG. 3, the lead wire 753 is bent along the axial direction of the insertion portion 751c in the insertion hole 752aa of the terminal surrounding portion 752a and fixed to the cap terminal 751.

  The gas sensor unit 600 is configured as described above.

  Needless to say, the present invention is not limited to the above embodiments, and various modifications are possible. For example, the gas sensor 21 is not limited to an oxygen sensor.

After applying a slurry made of a mixed powder of composite minerals such as SiO2, Al2O3, ZrO2 as a glaze to the ceramic enclosure (alumina), heat treatment was performed at the temperature and time shown in Table 1 respectively, and the outer surface of the ceramic enclosure 23 was applied. A glaze layer 231 was formed. And the form of the surface of this ceramic enclosure 23 (glaze layer 231) was image | photographed with the metal microscope.
Next, the gas sensor 21 shown in FIG. 1 is manufactured using the ceramic enclosures 23 shown in Table 1 in Examples 1 to 5 and Comparative Examples 1 to 4, and a sensor cap 700 is attached to the gas sensor 21. A gas sensor unit 600 shown in FIG. 2 was prepared. The gas sensor unit 600 was attached to a test container (tank) 500 shown in FIG. The test vessel has a screw hole through which the gas sensor 21 is inserted, and the screw hole 25b of the metal shell is screwed into the screw hole for attachment. Further, a temperature sensor was attached to the exposed portion of the ceramic enclosure 23 of the gas sensor 21, and a sensor cap 700 was fitted into the gas sensor 21 so as to surround the temperature sensor and the ceramic enclosure 23.
Then, the protector 26 protruding downward from the test container is heated with the flame F, and when the ceramic enclosure 23 reaches a predetermined temperature, water is poured into the test container with the shower SH from the upper part of the gas sensor unit 600, and the gas sensor unit 600 is submerged. The ceramic enclosure 23 was cooled rapidly. It drained after submergence, the sensor cap was removed, and the presence or absence of the crack of the ceramic enclosure 23 was determined visually. If there was no crack, the heating temperature by the flame F was raised and the same test was conducted, and the heating temperature when the crack occurred was defined as “cracking temperature”.

  The obtained results are shown in Table 1.

As shown in Table 1, in the case of each example heat-treated at a temperature of 1250 ° C. or more and 1300 ° C. or less, the surface of the glaze layer 231 is smooth, and when observed with a metal microscope, a needle-like crystal having a length of 50 μm or more Was not seen (FIG. 6 shows the surface state of Example 3). In the metal microscope image, a crystal having an aspect ratio (major axis / minor axis) of 2 or more was regarded as an acicular crystal.
On the other hand, in the case of Comparative Example 4 fired at a temperature lower than 1250 ° C., when the surface of the glaze layer 231 was observed with a metal microscope, a surface state having irregularities was seen, and the surface of the glaze layer 231 became rough. In the case of Comparative Examples 1 to 3 fired at a temperature exceeding 1300 ° C., a needle-like crystal having a length of 50 μm or more was observed on the surface of the glaze layer 231 with a metal microscope, and the surface of the glaze layer 231 became rough (see FIG. 7). Indicates the surface state of Comparative Example 1).
Moreover, about Examples 1-5, the cracking temperature was 340 degreeC or more, and heat resistance improved compared with Comparative Examples 1-4 with a cracking temperature of 320 degreeC. From this, it can be seen that when the heat treatment is performed at a temperature of 1250 ° C. or more and 1300 ° C. or less, the glaze layer 231 becomes dense and the thermal shock to the ceramic enclosure 23 is reduced.

DESCRIPTION OF SYMBOLS 21 Gas sensor 22 Gas detection element 23 Ceramic enclosure 23c Outer surface 231 of ceramic enclosure 23 Glazing layer 24 Terminal member 25 Metal fitting 29 Inner electrode 600 Gas sensor unit 700 Sensor cap 751 Cap terminal 752a Terminal enclosure 752aa Insertion hole O Axial direction

Claims (3)

A bottomed cylindrical gas detection element that extends in the axial direction and whose tip side is exposed to the gas to be measured;
A metal shell surrounding the periphery of the gas detection element;
In a cylindrical shape made of insulating ceramic, surrounding the periphery of the rear end side of the gas detection element, and a ceramic enclosure held by the metal shell in a form in which the rear end side of the gas detection element protrudes from the rear end of the metal shell,
A terminal member connected to an inner electrode formed on the inner peripheral surface of the gas detection element, outputting an output signal from the gas detection element to the outside, and held in a cylinder of the ceramic enclosure;
A gas sensor in which a glaze layer is formed on at least the outer surface of the ceramic enclosure, and no acicular crystals having a length of 50 μm or more are present on the glaze layer surface. A bottomed cylindrical gas detection element that extends in the axial direction and whose tip side is exposed to the gas to be measured;
A metal shell surrounding the periphery of the gas detection element;
In a cylindrical shape made of insulating ceramic, surrounding the periphery of the rear end side of the gas detection element, and a ceramic enclosure held by the metal shell in a form in which the rear end side of the gas detection element protrudes from the rear end of the metal shell,
A gas sensor manufacturing method comprising: a terminal member connected to an inner electrode formed on an inner peripheral surface of the gas detection element, outputting an output signal from the gas detection element to the outside, and held in a cylinder of the ceramic enclosure Because
A method of manufacturing a gas sensor, wherein a glaze is applied to at least an outer surface of the ceramic enclosure, and then a heat treatment is performed at a temperature of 1250 ° C. or more and 1300 ° C. or less to form a glaze layer on the ceramic enclosure. A gas sensor according to claim 1;
The cap terminal includes a cap terminal that is connected to the terminal member of the gas sensor and transmits the output signal to an external device, and an elastic member that has an insertion hole that surrounds the cap terminal and the rear end side of the ceramic enclosure. A gas sensor cap having a terminal surrounding portion for holding
A gas sensor unit comprising: