JP2006250925A - Gas sensor and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor of excellent durability by obtaining a gas sensor element capable of restraining blackening from being generated. <P>SOLUTION: A layered body 100 is formed to include the first two unburnt solid electrolytes 103, 107 serving as the first two solid electrolytes 103, 107 after burnt, and the first-fourth unburnt electrodes 102, 104, 106a, 106b, 108 serving as the electrodes 102, 104, 106a, 106b, 108 after burnt, in a layered body forming process. A molding 200 provided with an unburnt dense insulation layer 110 formed by applying paste comprising aluminum as a main component repeatedly a plurality of times, and serving as the dense insulation layer 110 after burnt is formed in an exposed part brought into a temperature condition of 600°C or less when at least the gas sensor element 300 of the layered body 100 is used, and exposed with the first two unburnt solid electrolytes 103, 107, in a molding forming process. The molding 200 is burnt to obtain the gas sensor element 300, in a burning process. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas sensor and a manufacturing method thereof.

  Patent Document 1 discloses a conventional gas sensor. This gas sensor has a gas sensor element having a detection part that extends in the axial direction and whose tip side is expected to be exposed to the gas to be measured, and a lead that is connected to the rear end side of the gas sensor element and extracts an output signal of the detection part. A member, a metal shell, an outer cylinder, and a protector are provided.

  The gas sensor element is a plate-like element formed by stacking rectangular solid electrolyte bodies and electrodes. The metal shell has a cylindrical shape, and the gas sensor element is inserted into the metal shell, and holds the gas sensor element so that at least the detection portion is exposed to the tip side. The outer cylinder is connected to the rear end side of the metal shell and accommodates the lead member therein. The protector is connected to the front end side of the metal shell and covers the detection part of the gas sensor element.

  This gas sensor can be manufactured as follows. First, as a laminated body forming step, an unfired solid electrolyte body that becomes a solid electrolyte body after firing and an unfired electrode that becomes an electrode after firing are laminated to form a laminated body.

Next, as a formed body forming step, an unfired insulating layer that becomes an insulating layer after firing is formed on the laminate to form a formed body. This unsintered insulating layer is formed on the outer peripheral surface of the laminate using a paste mainly composed of alumina (Al ₂ O ₃ ).

  And as a baking process, a molded object is baked and a gas sensor element is obtained. And this gas sensor element and a ceramic heater are bonded together. This ceramic heater is provided to heat the detection unit and to activate the detection unit because the gas sensor element is generally activated at a high temperature of 600 ° C. or higher. Moreover, a metal shell, an outer cylinder, a protector, etc. are prepared and assembled.

  The gas sensor thus obtained is attached to an exhaust system such as an exhaust pipe of an engine, for example, and is used for detecting a measurement target gas in the exhaust gas.

  At this time, since the exhaust gas contains water droplets, oil droplets, and the like, even if the detection part of the gas sensor element is covered with the protector, some of the water droplets may adhere to the gas sensor element. Further, depending on the mounting position of the gas sensor, the condensed water condensed on the wall surface of the protector may adhere to the gas sensor element. In these cases, since the gas sensor element is exposed to exhaust gas or heated by a ceramic heater, a large temperature difference is generated between the portion where water droplets or the like are attached and its surroundings, and the thermal shock caused by this difference. May cause cracks, but the insulating layer formed on the outer peripheral surface prevents the cracks from occurring.

JP 2003-322632 A

  In recent years, a gas sensor such as that disclosed in Patent Document 1 is also mounted on an exhaust pipe of a diesel engine, and is used to detect a measurement target gas in the exhaust gas. The exhaust gas of this diesel engine contains a lot of soot and carbon in addition to water droplets and oil droplets. As a result, blackning occurs in the gas sensor element, and there is a possibility that the gas sensor element may be cracked or output may be abnormal.

  That is, soot or carbon in the exhaust gas adheres to the gas sensor element and itself becomes a conductor. At this time, an insulating layer is provided in the gas sensor element as in Patent Document 1, and the metal shell and the gas sensor element are normally insulated, but when forming an unfired insulating layer in the laminate, Deviation may occur with respect to the position where the unsintered insulating layer is formed, and the unsintered solid electrolyte body may be exposed to the outside. In addition, when pinholes or the like are generated in the unsintered insulating layer, the unsintered solid electrolyte body may be exposed to the outside. Then, the electrode located inside the gas sensor element and the metal shell are electrically connected to each other by the solid electrolyte body, the bag, and the carbon, and since the gas sensor element has a potential, a current flows through both of them. Then, blackening (blackening) occurs in which zirconia in the solid electrolyte body is reduced to zirconium. The gas sensor element in which blackening has occurred in this way becomes brittle and easily cracks, and an abnormality occurs in the output of the gas sensor due to a change in characteristics.

  The present invention has been made in view of the above-described conventional situation, and obtains a gas sensor element that suppresses the occurrence of blackening, and provides a gas sensor having excellent durability and a method for manufacturing the same. It is said.

  The gas sensor manufacturing method of the present invention includes a plate-like gas sensor element in which a solid electrolyte body and an electrode are laminated,

  A gas sensor manufacturing method comprising: a casing surrounding the periphery of the gas sensor element;

  A laminate forming step of forming a laminate including an unsintered solid electrolyte body to be the solid electrolyte body after firing and an unsintered electrode to be the electrode after firing;

  Formed by repeatedly applying a paste containing alumina as a main component a plurality of times to an exposed portion where the temperature of the laminate is less than 600 ° C. when the gas sensor element is used and the unsintered solid electrolyte body is exposed. A molded body forming step of forming a molded body having an unfired dense insulating layer that becomes a dense insulating layer after firing,

  And a firing step of firing the molded body to obtain the gas sensor element.

  The manufacturing method of this invention is equipped with the laminated body formation process, the molded object formation process, and the baking process.

  In the laminated body forming step, a laminated body including an unfired solid electrolyte body that becomes a solid electrolyte body after firing and an unfired electrode that becomes an electrode after firing is formed. The unsintered solid electrolyte body contains zirconia as a main component. In the present specification, the “main component” means that the content of the component is the largest.

  In the molded body forming step, a molded body including an unfired dense insulating layer mainly composed of alumina that becomes a dense insulating layer after firing is formed on at least an exposed portion of the laminated body where the unfired solid electrolyte body is exposed. In particular, the unfired dense insulating layer is repeatedly applied with a paste mainly composed of alumina a plurality of times. As a result, when the green dense insulating layer is formed on the laminate, even if a deviation occurs from the position where the green dense insulating layer is originally formed, the green solid electrolyte body is applied multiple times. Can be prevented from being exposed to the outside. Moreover, even if pinholes or the like are generated in the previously formed unfired dense insulating layer by being applied multiple times, the unfired dense insulating layer that is formed later fills the pinholes and unfired solid electrolyte The body can be prevented from being exposed to the outside.

  According to the test results of the inventors, soot and carbon are accumulated on the surface of the gas sensor element in a part where the soot is hardly combusted during use of the gas sensor element and is in a temperature state of less than 600 ° C. In other words, the gas sensor element is heated by the exhaust gas or the ceramic heater, but it is considered that soot and carbon are not burned and accumulated in a portion where the temperature is less than 600 ° C.

  It is difficult for soot to be burned at less than 600 ° C as disclosed in JP2003-80031, JP20031666412, JP2003-106205, JP2003-35129, and JP2004-293416. This is also known in Japanese Patent Laid-Open No. 2004-162611. In the gas sensor, the portion of the gas sensor element is closest to a casing such as a metal shell or a protector. Therefore, in the manufacturing method of the present invention, an unfired dense insulating layer is formed at least on the exposed portion of the laminate that is in a temperature state of less than 600 ° C. when the gas sensor element is used. Thereby, an unfired dense insulating layer is formed only at a portion where the soot and carbon of the gas sensor element are accumulated without burning, and the unfired solid electrolyte body can be suppressed from being exposed to the outside.

  Note that the unfired dense insulating layer according to the present invention can also be formed on the tip side where the gas sensor element is expected to be exposed to the measurement target gas. That is, the unfired dense insulating layer may be formed on the entire laminate. In this case, it is possible to prevent not only blackening but also generation of cracks in the gas sensor element due to moisture.

  And in a baking process, a molded object is baked and a gas sensor element is obtained.

  The gas sensor element thus obtained is attached to a casing that surrounds the gas sensor element, is attached to the exhaust system of the engine as a part of the gas sensor, and is used to detect a specific gas in the measurement target gas. In this case, the gas sensor element can suppress conduction between the electrode disposed inside the gas sensor element and the casing even if soot or carbon accumulates in a portion where the temperature is lower than 600 ° C. during use. For this reason, blackening hardly occurs in the gas sensor element.

  Therefore, according to the manufacturing method of the present invention, it is possible to manufacture a gas sensor element that suppresses the occurrence of blackening. Since the gas sensor element thus obtained does not easily generate blackening, a gas sensor exhibiting excellent durability can be obtained.

  As a method for forming the unfired dense insulating layer in the molded body forming step, screen printing, dipping (dip), brush coating, transfer, green sheet sticking, and the like can be employed.

  The unfired dense insulating layer is mainly composed of alumina. Specifically, a solvent such as acetone or toluene and a binder such as polyvinyl butyral or CMC can be mixed. Only one type of solvent and binder may be used, or two or more types may be used in combination.

  Furthermore, the production method of the present invention exhibits a remarkable effect when a dense insulating layer is formed by screen printing in the formed body forming step. Formation of the unfired dense insulating layer is facilitated by screen printing. At this time, a net is used for screen printing, but the intersection of the wires constituting the net tends to cause pinholes in the unfired dense insulating layer. Therefore, in this screen printing, if the unfired dense insulating layer is formed a plurality of times, the intersections of the wires at each time are difficult to overlap and pinholes are unlikely to occur, so that the unfired solid electrolyte body is exposed to the outside. It can suppress and generation | occurrence | production of blackening can be suppressed.

  In the production method of the present invention, the unfired dense insulating layer preferably has a thickness of 2 μm or more. If the thickness is less than 2 μm, it is difficult to prevent current flow between the solid electrolyte body and the casing, and it is difficult to achieve the effects of the present invention. A dense insulating layer having a thickness of 2 μm or more exhibits a sufficient insulation resistance. Practically, the thickness of the unfired dense insulating layer can be reduced to about 30 μm.

  In the molded body forming step, it is preferable that the thickness of the first unfired dense insulating layer formed for the first time among the unfired dense insulating layers is 2 μm or more. If pinholes and misalignment do not overlap, if the initial thickness is 2 μm or more, the pinhole that occurred first time can be filled up to that thickness by the next application. This is because an unfired dense insulating layer having a total thickness of at least 2 μm can be obtained, and the effects of the present invention can be obtained as described above.

  The gas sensor of the present invention includes a plate-like gas sensor element in which a solid electrolyte body and an electrode are laminated,

  A gas sensor having a casing surrounding the gas sensor element;

  The gas sensor element is an element main body and both side surfaces extending in the stacking direction of the element main body and facing the inner peripheral surface of the casing via a gap, and at least less than 600 ° C. when the gas sensor element is used. And a dense insulating layer mainly composed of alumina, which is provided on both side surfaces which are in a temperature state, and is integrally fired with the element main body and the both side surfaces of the element main body cannot be visually recognized from its own surface. Features.

  The gas sensor of the present invention is integrally fired with the element body on both side surfaces of the element body that extend in the stacking direction and face the inner peripheral surface of the casing via a gap, and from both surfaces of the element body. A dense insulating layer whose main component is alumina whose surface is not visible is provided. Thereby, even if soot or carbon accumulates on the dense insulating layer, it is possible to suppress conduction between the electrode disposed inside the gas sensor element and the casing. For this reason, it is difficult to cause blackening in the gas sensor element, and a gas sensor that exhibits excellent durability can be obtained.

  Further, since the dense insulating layer is mainly composed of alumina and is integrally fired with the element body, the dense insulating layer is firmly fixed to the element body.

  In particular, according to the test results of the inventors, soot and carbon are accumulated on the surface of the gas sensor element in a region where the soot is not easily burned when the gas sensor element is used and the temperature is less than 600 ° C. In other words, the gas sensor element is heated by the exhaust gas or the ceramic heater, but it is considered that soot and carbon are not burned and accumulated in a portion where the temperature is less than 600 ° C.

  It is difficult for soot to be burned at less than 600 ° C as disclosed in JP2003-80031, JP20031666412, JP2003-106205, JP2003-35129, and JP2004-293416. This is also known in Japanese Patent Laid-Open No. 2004-162611. In the gas sensor, the portion of the gas sensor element is closest to a casing such as a metal shell or a protector. Therefore, in the gas sensor of the present invention, dense insulating layers are formed on both side surfaces of the element body that is at a temperature lower than 600 ° C. at least when the gas sensor element is used.

  In addition, the dense insulating layer in which the surface of the element body cannot be visually recognized from its own surface can be determined by taking a gas sensor element with an SEM photograph and determining whether or not a through-hole toward the element body is formed in the SEM photograph. it can. Further, when carbon is attached to the surface of the dense insulating layer so that the resistance between the casing and the surface of the dense insulating layer is 20 kΩ, and the gas sensor is heated in a rich atmosphere so that the gas sensor element temperature is 780 ° C., You may judge by resistance with a casing becoming 500 kohm or more.

  It should be noted that the dense insulating layer according to the present invention can also be formed on the tip side where the gas sensor element is expected to be exposed to the measurement target gas. That is, the dense insulating layer may be formed on the entire gas sensor element. In this case, it is possible to prevent not only blackening but also generation of cracks in the gas sensor element due to moisture.

  In the gas sensor of the present invention, the dense insulating layer preferably has a thickness of 2 μm or more. If the thickness is less than 2 μm, it is difficult to prevent the solid electrolyte body and the casing from being energized, and it is difficult to achieve the effects of the present invention. A dense insulating layer having a thickness of 2 μm or more exhibits a sufficient insulation resistance. Practically, it is possible to reduce the thickness of the dense insulating layer to about 30 μm.

    Hereinafter, Examples 1 and 2 embodying the present invention will be described in comparison with Comparative Examples 1 and 2. The gas sensors of Examples 1 and 2 and Comparative Examples 1 and 2 are oxygen sensors.

  First, as a laminate forming process, a laminate 100 having a structure shown in FIG. 1 was formed. At this time, the first unfired protective layer 150, the unfired substrate 101, the first unfired electrode 102, the first external electrode 301, the first unfired solid electrolyte body 103, and the second unfired layer are disposed in the mold in order from the bottom. Sintered electrode 104, unsintered insulating layer 105, second and third external terminals 302 and 303, third unsintered electrodes 106a and 106b, second unsintered solid electrolyte body 107, fourth unsintered electrode 108 and second unsintered protection Layer 109 is provided.

The first unsintered protective layer 150 is composed of 97% by mass of a mixed powder of alumina powder and silica powder (the breakdown is 99.7% by mass of alumina powder and 0.3% by mass of silica powder) and a sintering regulator (SiO ₂ -MgO-CaO-based flux) 3% by mass of the slurry dispersed by wet mixing. This slurry was formed into a sheet-like material having a thickness of 0.4 mm by a sheet forming method using a doctor blade device, and a first unfired protective layer 150 was obtained. And this 1st unbaking protective layer 150 was 140 mm x 140 mm, and it provided in the shaping | molding die.

The unfired substrate 101 is made of a slurry in which raw material powder and a plasticizer are dispersed by wet mixing. The raw material powder is composed of 97% by mass of zirconia powder and a total of 3% by mass of silica (SiO ₂ ) powder and alumina powder as a sintering regulator. The plasticizer consists of 11 parts by weight of butyral resin and 6 parts by weight of dibutyl phthalate (DBP) added to 100 parts by weight of the raw material powder. An unfired substrate 101 having the same size as the first unfired protective layer 150 was provided in the mold.

  The first unsintered electrode 102 is made of platinum paste of 90% by mass of platinum and 10% by mass of zirconia powder. The first green electrode 102 was formed by screen printing using this platinum paste. The first unsintered electrode 102 includes an electrode portion 102a formed on the front end side, a lead portion 102b that is integral with the electrode portion 102a and extends rearward in the axial direction, and an axial rear portion that is integral with the lead portion 102b. It consists of the connection part 102c formed in the end side.

  The first unsintered solid electrolyte body 103 is made of the same slurry as the unsintered substrate 101. The first green solid electrolyte body 103 having the same size as the first green protective layer 150 and the green substrate 101 was provided in the mold.

  The second green electrode 104 is the same material as the first green electrode 102. The second unsintered electrode 104 includes an electrode portion 104a formed on the front end side, a lead portion 104b that is integral with the electrode portion 104a and extends rearward in the axial direction, and an axially rear portion that is integral with the lead portion 104b. It consists of the connection part 104c formed in the end side.

  The unsintered insulating layer 105 includes an unsintered main body 105a and an unsintered diffuser 105b. The unfired main body 105 a is made of the same slurry as the first unfired protective layer 150. In the unfired main body 105a, a gas detection chamber 105c is formed at the same position in the height direction as the electrode portions 102a and 104a of the first and second unfired electrodes 102 and 104. The gas detection chamber 105c communicates with the outside on both sides in the width direction through the unsintered diffuser 105b. The unsintered diffuser 105b is made of a slurry in which 100% by mass of alumina powder is dispersed by wet mixing.

  The third green electrodes 106a and 106b are made of the same material as the first and second green electrodes 102 and 104. The third unsintered electrode 106a includes an electrode portion 106c formed on the front end side, a lead portion 106d that is integral with the electrode portion 106c and extends rearward in the axial direction, and an axial rear end that is integral with the lead portion 106d. And a connecting portion 106e formed on the side. The third green electrode 106b is formed in parallel with the connecting portion 106e of the third green electrode 106a in the width direction.

  The second green solid electrolyte body 107 is the same material as the first green solid electrolyte body 103. An insertion hole 107 a is provided in the thickness direction on the rear end side of the second unsintered solid electrolyte body 107. A second unfired solid electrolyte body 107 having the same size as the first unfired protective layer 150, unfired substrate 101, first unfired solid electrolyte body 103, and unfired insulating layer 105 was provided in the mold.

  The fourth green electrode 108 is the same material as the first to third green electrodes 102, 104, 106. The fourth unsintered electrode 108 includes an electrode portion 108a formed on the front end side, a lead portion 108b that is integral with the electrode portion 108a and extends rearward in the axial direction, and an axial rear end that is integral with the lead portion 108b. And a connecting portion 108c formed on the side.

  The second unsintered protective layer 109 includes an unsintered body 109a and an unsintered porous body 109b. The unfired main body 109 a is made of the same slurry as the unfired main body 105 a of the first unfired protective layer 150 and the unfired insulating layer 105. A second unfired protective layer 109 was provided in the mold. An unfired porous body 109b is provided at the tip of the unfired main body 109a at the same position in the height direction as the gas detection chamber 105c serving as a detection portion and the electrode portions 106c and 108a of the unfired electrodes 106 and 108. The unsintered porous body 109b is made of a slurry in which 83% by mass of alumina powder, 3% by mass of silica as a sintering regulator, and 14% by mass of platinum powder are dispersed by wet mixing. As a result, the same size as that of the first unfired protective layer 150, the unfired substrate 101, the first unfired solid electrolyte body 103, the unfired insulating layer 105, and the second unfired solid electrolyte body 107 is obtained.

  And these were pressurized by 150 MPa, and after crimping | bonding, it cut | disconnected by the magnitude | size shown in FIG. 1, and obtained the 8 laminated bodies 100 from 1 shaping | molding die.

Next, a molded body forming step was performed. That is, 97% by mass of mixed powder of alumina powder and silica powder (the breakdown is 99.7% by mass of alumina powder and 0.3% by mass of silica powder) and a sintering regulator (SiO ₂ —MgO—CaO based flux) A paste in which 3% by mass was dispersed by wet mixing was prepared, and this paste was used to screen-print twice on the laminate 100 to form an unfired dense insulating layer 110 as shown in FIG.

  First, in the first screen printing, the unsintered diffuser 105b was covered with masking, and as shown in FIG. 3, the first unsintered dense insulating layer 111 having a thickness of 10 to 20 μm was formed on the entire side surface of the laminate 100. .

  Furthermore, in the second screen printing, 8 mm from the tip was covered with masking, and a second unfired dense insulating layer 112 having a thickness of 10 to 20 μm was formed on the side portion on the rear side. The reason why the second unfired dense insulating layer 112 is formed on the rear side from 8 mm from the tip is that it includes a portion that is in a temperature state of less than 600 ° C. when the gas sensor element 300 described later is used. In this way, as shown in FIG. 2, an unfired dense insulating layer 110 was formed on the laminated body 100 to obtain a molded body 200.

  And as a baking process, the molded object 200 is baked at 1350-1550 degreeC. Thus, as shown in FIG. 3, a gas sensor element 300 for detecting the oxygen concentration in the exhaust gas is obtained. Note that the second dense insulating layer 112 formed in the fired gas sensor element 300 is formed in a portion from the tip to 6.5 mm by shrinking.

  The first unsintered protective layer 150 shown in FIG. 1 becomes the first protective layer 150 by the firing process. The unfired substrate 101 becomes the substrate 101 for maintaining the strength of the gas sensor element 300. The unsintered electrode 102 becomes the reference electrode 102 including the electrode portion 102a, the lead portion 102b, and the connection portion 102c. The connection part 102 c of the reference electrode 102 is connected to the first external terminal 301. The first unsintered solid electrolyte body 103 becomes the first solid electrolyte body 103. The second unsintered electrode 104 becomes the measurement electrode 104 including the electrode part 104a, the lead part 104b, and the connection part 104c. The unsintered body 105a of the unsintered insulating layer 105 becomes the insulating layer 105a, and the unsintered diffuser 105b of the unsintered insulating layer 105 becomes the porous diffusion rate limiting body 105b. The gas detection chamber 105c of the insulating layer 105a communicates with the outside through the diffusion rate limiting body 105b on both sides of the insulating layer 105 in the width direction. The diffusion rate limiting body 105b realizes gas diffusion between the outside and the gas detection chamber 105c under a predetermined rate limiting condition. The third unsintered electrode 106a becomes a pumping electrode 106a including an electrode portion 106c, a lead portion 106d, and a connecting portion 106e. The connection part 106 e of the pumping electrode 106 a is connected to the second external terminal 302. The third unsintered electrode 106b becomes a signal extraction terminal 106b. The signal extraction terminal 106 b is connected to the third external terminal 303. The second unsintered solid electrolyte body 107 becomes the second solid electrolyte body 107. The fourth unsintered electrode 108 becomes a pumping electrode 108 including an electrode portion 108a, a lead portion 108b, and a connection portion 108c. The connecting portion 108 c of the pumping electrode 108 is connected to the signal extraction terminal 106 b through the insertion hole 107 a of the second solid electrolyte body 107. The green body 109a of the second green protective layer 109 becomes an insulating protective layer 109a for protecting the second solid electrolyte body 107, and the green porous body 109b of the second green protective layer 109 poisons the pumping electrode 108. It becomes the porous electrode protective layer 109b for protecting from. Further, the green dense insulating layer 110 shown in FIG. 2 becomes the dense insulating layer 110.

  Moreover, the metal shell 3, the outer cylinder 8, the protector 4, etc. are prepared and assembled. In this way, the gas sensor shown in FIG. 4 is obtained. The gas sensor includes a gas sensor element 300, a ceramic heater 2 stacked on the gas sensor element 300, a metal shell 3 that holds the gas sensor element 300 and the like inside, a protector 4 that is attached to the tip of the metal shell 3, and the like. . In Example 1, among the directions along the axis of the gas sensor element 300 shown in FIG. 4, the side exposed to the measurement gas (exhaust gas) (the lower side in the figure) is the “tip side”, and the opposite direction. The side toward (the upper side in the figure) will be described as the “rear end side”.

  The gas sensor element 300 is arranged so as to extend in the axial direction. The ceramic heater 2 is laminated on the gas sensor element 300 via a bonding layer (not shown). The ceramic heater 2 is disposed so as to extend in the axial direction, and includes a heating resistor mainly composed of Pt inside a plurality of alumina green sheets. When the ceramic heater 2 is energized through the heater lead wires 11 and 12, the heating resistor generates heat and activates the gas sensor element 300.

  A support rod 19 is bonded to the rear end side of the gas sensor element 300. The support rod 19 is a member that extends in parallel with the axial direction of the gas sensor element 300 and has a substantially U-shaped cross section in a direction orthogonal to the extended axial direction. The concave surface side of the supporting soot tube 19 is bonded toward the side surface side of the gas sensor element 300. As the material of the support rod 19, a material close to the thermal expansion coefficient of the glass component constituting the seal member 65, specifically, alumina is used. The supporting soot tube 19 is provided to suppress the occurrence of cracks in the gas sensor element 300 due to a difference in thermal expansion between the gas sensor element 300 and the seal member 65.

  The metal shell 3 is made of SUS430, and has a male screw 31 for attaching the gas sensor to the exhaust pipe, and a hexagonal portion 32 to which an attachment tool is applied at the time of attachment. Further, the metal shell 3 is provided with a metal side step portion 33 projecting radially inward, and this metal side step portion 33 is made of alumina for insulation from the gas sensor element 300 via the packing 5. The cylindrical member 6 is supported. Specifically, a protruding portion 61 that protrudes radially outward of the cylindrical member 6 is supported by the metal fitting side step portion 33. On the other hand, a filling member 34 made of talc powder is disposed between the inner surface of the metal shell 3 and the outer surface of the cylindrical member 6 on the rear end side of the protruding portion 61, and a sleeve on the rear end side of the filling member 34. 35 is arranged in a state of being inserted into the metal shell 3.

  Inside the cylindrical member 6, an alumina holder 62 and an adhesive member 63 for fixing the holder 62, the gas sensor element 300, and the ceramic heater 2 are disposed in order from the tip side. Further, the second filling member 64 made of talc powder is filled between the cylindrical member 6 and the gas sensor element 300 and the ceramic heater 2, and arranged at the rear end side so as to surround the sensor element 300 and the ceramic heater 2. And a sealing member 65 made of a glass seal. The second filling member 64 is obtained by melting and solidifying an active mixed powder containing 12% by mass of a glass component. The sealing member 65 is formed by melting and solidifying crystallized glass powder (silica, zinc magnesium borate glass).

  Furthermore, the front end side of the inner cylinder 7 made of SUS304 is inserted inside the rear end side of the metal shell 3. The inner cylinder 7 is formed by caulking the rear end portion 36 of the metal shell 3 in the inner front end direction with the opening end 71 having an enlarged diameter on the front end inserted in the rear end side inside the metal shell 3. 3 is fixed. Further, the filling member 34 is compressed and filled through the sleeve 35 by crimping the rear end portion 36 of the metal shell 3. The inner cylinder 7 protects the rear end portion of the cylindrical member 6. Further, the inner cylinder 7 supports a separator 9 disposed on the rear end side from the front end side.

  The outer cylinder 8 is made of SUS304 formed in a cylindrical shape, and the distal end side is coaxially connected to the inner cylinder 7. The outer cylinder 8 and the inner cylinder 7 are arranged so as to overlap from the outside, and at least a part of the overlapping portion is caulked toward the inner side in the circumferential direction, thereby being connected to each other.

  On the other hand, as shown in FIG. 5, a metal protector 4 having a plurality of gas intake holes 4a is provided on the outer periphery on the front end side of the metallic shell 3 to cover the distal end portion of the gas sensor element 300 protruding from the distal end of the metallic shell 3. Are attached by welding. This protector 4 has a double structure, and has a bottomed cylindrical outer protector 41 having a uniform outer diameter on the outer side, and the outer diameter of the rear end is larger than the outer diameter of the front end on the inner side. The formed bottomed cylindrical inner protector 42 is disposed. The outer surface of the bottom portion of the inner protector 42 is spot welded to the inner surface of the bottom portion of the outer protector 41, and the outer protector 41 and the inner protector 42 are integrated.

  A separator 9 is inserted into the outer cylinder 8. The separator 9 has an insertion hole 91 through which the heater lead wires 11 and 12 and the element lead wires 13 to 15 are inserted from the front end side to the rear end side.

  In the insertion hole 91, heater lead wires 11 and 12 and element lead wires 13 to 15, and external terminals 301 to 303 of the gas sensor element 300 and connection terminals 16 connected to external terminals of the ceramic heater 2 are provided. A connecting member 17 to be connected is accommodated. These heater lead wires 11 and 12 and element lead wires 13 to 15 are externally connected to a connector (not shown). Electric signals are input and output between the external devices such as the ECU and the lead wires 11, 12, 13 to 15 through this connector. Moreover, although not shown in detail in each lead wire 11, 12, 13-15, it has the structure which showed the conducting wire with the insulating film which consists of resin.

  Furthermore, a substantially cylindrical rubber cap 18 for closing the opening on the rear end side of the outer cylinder 8 is disposed on the rear end side of the separator 9. The rubber cap 18 is fixed to the outer cylinder 8 by caulking the outer periphery of the outer cylinder 8 toward the radially inner side in a state where the rubber cap 18 is mounted in the rear end of the outer cylinder 8. An insertion hole 18a for inserting the heater lead wires 11 and 12 and the element lead wires 13 to 15 is also provided in the rubber cap 18 from the front end side to the rear end side.

  In the gas sensor having the above configuration, the distance (mm) from the tip of the gas sensor element 300 and the temperature during use (° C.) were measured. The results are shown in FIG.

  From FIG. 6, it can be seen that the gas sensor element 300 has a portion around 6.5 mm from the tip that is in a temperature state of 600 ° C. or higher during use. For this reason, it can be seen that the rear side of the gas sensor element 300 is in an environment in which the temperature is less than 600 ° C. during use, and soot is accumulated and blackening is likely to occur.

  Next, in this gas sensor, an endurance test was performed to confirm whether or not actual blackening was performed under conditions that facilitate blackening. First, the dense insulating layer 110 of the gas sensor element 300 created in Example 1 was photographed with an SEM photograph. The results are shown in FIG. FIG. 7 shows that no pinhole is generated in the dense insulating layer 110. Next, the gas sensor element 300 was masked with a masking tape up to 8 mm from the tip and sprayed with carbon spray. At this time, carbon spray was sprayed until the surface of the gas sensor element 300 and the metal shell 3 became conductive (1 kΩ or less). And the masking tape of the front-end | tip of the gas sensor element 300 was peeled off, and the protector 4 was fastened.

  A gas sensor was attached to a furnace having A / F (air-fuel ratio) = 11.5 (rich) and a furnace temperature of 450 ° C., and control was performed for 14 hours. The rich test is done to prevent carbon from burning and changing the sample state. After completion of the control, the gas sensor element 300 of the gas sensor was taken out, and the carbon was peeled off using an ultrasonic cleaner. And the blackening of the gas sensor element 300 was confirmed with the metal microscope. The results are shown in Table 1.

  Table 1 shows that the gas sensor of Example 1 does not blacken the gas sensor element 300.

  In the gas sensor of Example 2, screen printing was performed four times on the laminate 100 described above. In the first screen printing, the unsintered diffuser 105 b was covered with masking, and the first unsintered dense insulating layer 111 was formed on the molded body 100. In the second and subsequent screen printings, 8 mm from the tip was covered with masking, and the second unfired dense insulating layer 112 was formed on the rear side. Other configurations are the same as those of the first embodiment. The gas sensor of Example 2 was also subjected to an endurance test as in Example 1. The results are shown in Table 1.

  From Table 1, it can be seen that the gas sensor of Example 2 also does not blacken the gas sensor element 300.

Comparative Example 1

  On the other hand, the gas sensor of Comparative Example 1 performed screen printing once on the laminate 100. That is, the same screen printing as the first time in the first and second embodiments is performed. Other configurations are the same as those of the first embodiment. And the dense insulating layer 110 of the gas sensor element 300 produced in the comparative example 1 was image | photographed with the SEM photograph. The results are shown in FIG. FIG. 8 shows that pinholes are generated in the dense insulating layer 110, and it can be seen that the first solid insulating layer 103 or the second solid electrolyte layer is exposed by these pinholes. Next, the gas sensor of Comparative Example 1 was also subjected to an endurance test as in Example 1. The results are shown in Table 1.

  From Table 1, it can be seen that the gas sensor of Comparative Example 1 causes blacking in the gas sensor element 300.

Comparative Example 2

  In the gas sensor of Comparative Example 2, screen printing was not performed on the side surface of the laminate 100. Other configurations are the same as those of the first embodiment. The gas sensor of Comparative Example 2 was also subjected to an endurance test as in Example 1. The results are shown in Table 1.

  From Table 1, it can be seen that the gas sensor of Comparative Example 2 causes blacking in the gas sensor element 300. This is because the gas sensor element 300 directly exposes the first unsintered solid electrolyte body 103 or the second unsintered solid electrolyte body 107.

  From the above, it can be seen that if alumina is printed on the side surface of the gas sensor element 300 a plurality of times, pinholes are not formed in the dense insulating layer 110 and blackening does not occur in the gas sensor element 300.

  The gas sensor according to the present invention can be widely used for exhaust gas sensors (oxygen sensors, hydrocarbon sensors, NOx sensors, etc.) of engines, particularly diesel engines, and other various sensors.

It is a model exploded perspective view of the laminated body for gas sensor elements of Example 1 grade | etc.,. It is a model perspective view of the molded object for gas sensor elements of Example 1 grade | etc.,. FIG. 3 is a schematic cross-sectional view of a gas sensor element after firing when the gas sensor element laminate of Example 1 or the like is cut along the line III-III in FIG. 1. It is sectional drawing of the gas sensor of Example 1 grade | etc.,. It is a principal part expanded sectional view of gas sensors, such as Example 1. FIG. It is a graph which shows the relationship between the distance from the front-end | tip in the gas sensor element of Example 1, and temperature. It is a SEM photograph after the endurance test of the gas sensor element of Example 1. It is a SEM photograph after the endurance test of the gas sensor element of comparative example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 103 ... 1st unbaked solid electrolyte body, 1st solid electrolyte body 107 ... 2nd unbaked solid electrolyte body, 2nd solid electrolyte body 102 ... 1st unbaked electrode, reference electrode 104 ... 2nd unbaked electrode, measuring electrode 106a ... third unsintered electrode, pumping electrode 106b ... third unsintered electrode, signal extraction terminal 108 ... fourth unsintered electrode, pumping electrode 100 ... laminated body 110 ... unsintered dense insulating layer, dense insulating layer 200 ... molding Body 300 ... Gas sensor element

Claims (6)

A plate-like gas sensor element in which a solid electrolyte body and an electrode are laminated;
A gas sensor manufacturing method comprising: a casing surrounding the periphery of the gas sensor element;
A laminate forming step of forming a laminate including an unsintered solid electrolyte body to be the solid electrolyte body after firing and an unsintered electrode to be the electrode after firing;
Formed by repeatedly applying a paste containing alumina as a main component a plurality of times to an exposed portion where the temperature of the laminate is less than 600 ° C. when the gas sensor element is used and the unsintered solid electrolyte body is exposed. A molded body forming step of forming a molded body having an unfired dense insulating layer that becomes a dense insulating layer after firing,
And a firing step of firing the molded body to obtain the gas sensor element.   The method for manufacturing a gas sensor according to claim 1, wherein the green compact insulating layer is formed by screen printing in the molded body forming step.   3. The method of manufacturing a gas sensor according to claim 2, wherein the green dense insulating layer has a thickness of 2 [mu] m or more.   4. The method for manufacturing a gas sensor according to claim 2, wherein, in the formed body forming step, a thickness of the first unfired dense insulating layer formed for the first time among the unfired dense insulating layers is 2 μm or more. 5. . A plate-like gas sensor element in which a solid electrolyte body and an electrode are laminated;
A gas sensor having a casing surrounding the gas sensor element;
The gas sensor element is an element main body and both side surfaces extending in the stacking direction of the element main body and facing the inner peripheral surface of the casing via a gap, and at least less than 600 ° C. when the gas sensor element is used. And a dense insulating layer mainly composed of alumina, which is provided on both side surfaces which are in a temperature state, and is integrally fired with the element main body and the both side surfaces of the element main body cannot be visually recognized from its own surface. Characteristic gas sensor.   The gas sensor according to claim 5, wherein the dense insulating layer has a thickness of 2 μm or more.