JP2009115781A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide gas sensor which can inhibit any crack appearance on detection element body caused by crack arisen in base end of porous protective layer. <P>SOLUTION: The gas sensor 100 includes main fitting 110 and the detection element body 201 held by this main fitting, the porous protective layer 240 covering tip side of the detection element body 201, and inner protector 161 provided with inside through-hole 167 which directly encloses element nose part 202 protruding from tip of the main fitting on the detection element body 201 to introduce gas to be measured. Among these parts, the porous protective layer 240 consists of covering section 242 and reduced bore section 247 arranged on the base end side rather than the covering section, thickness of which will gradually be tapered as it goes towards the base end side. This reduced bore section 247 is allocated on the base end side rather than the inside through-hole 167. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a gas sensor including a cylindrical metal shell extending in the axial direction and a detection element body that extends in the axial direction and is held inside in the radial direction, and in particular, protects the front end side of the detection element body in the axial direction with porous protection. Relates to a gas sensor coated with a layer.

Conventionally, a detection element that is attached to an exhaust pipe of an automobile and used to change the electromotive force or the resistance value according to the concentration of a specific gas (for example, nitrogen oxide or oxygen) in the exhaust gas. There is known a gas sensor comprising:
In the detection element of such a gas sensor, a porous protective layer made of a porous ceramic is used for the tip of the detection element body for the purpose of preventing the occurrence of cracks due to thermal shock when water droplets in the exhaust gas adhere. It is known to coat with. By providing a porous protective layer, the water droplets adhering to the detection element slowly permeate while being dispersed in this porous protective layer, so that a large thermal shock is unlikely to occur in the detection element body, The generation of cracks can be prevented. For example, a gas sensor having such a porous protective layer is disclosed in Patent Document 1 (see FIG. 1 of Patent Document 1 and the description thereof).

JP 2007-33374 A

  However, the conventional porous protective layer has a configuration in which the base end has a sharp corner. For this reason, the base end may be chipped due to vibration or impact during use. If the porous protective layer becomes thin due to this chipping, or if water droplets in the exhaust gas adhere to the exposed part of the detection element body, cracks will occur in this part of the detection element body due to thermal shock at that time was there.

  The present invention has been made in view of the current situation, and provides a gas sensor that prevents cracks from occurring in the detection element body due to chipping at the base end of the porous protective layer. Objective.

  The solution includes a metal shell having a cylindrical shape extending in the axial direction, and an element projecting portion protruding from the tip of the metal shell, and extending in the axial direction and held on the radially inner side of the metal shell. A detection element body, a porous protective layer covering the front end side of the detection element body, and attached to the metal shell so as to directly surround the porous protection layer. And a protector provided with an introduction hole for introducing the gas to be measured on the side wall disposed in the cover, wherein the porous protective layer is provided on the base end side with respect to the covering portion and the covering portion. The reduced diameter portion is a gas sensor that is disposed closer to the proximal end side than any of the introduction holes.

In the gas sensor of the present invention, in the porous protective layer, the reduced diameter portion located on the proximal end side with respect to the covering portion is configured so that the thickness gradually decreases toward the proximal end side. In other words, the reduced diameter portion does not have a sharp corner as at the base end of the conventional porous protective layer. For this reason, it is possible to prevent the reduced-diameter portion from being chipped due to vibration or impact during use, and the porous protective layer in this portion to become thin, or the detection element body to be exposed in this portion. Therefore, even if water droplets in the exhaust gas adhere to the reduced diameter portion, the detection element main body is hardly cracked.
In addition, since the reduced diameter portion is disposed on the proximal end side with respect to the introduction hole provided in the side wall of the protector that directly surrounds the element protruding portion, water droplets that have passed through the introduction hole are unlikely to adhere to the reduced diameter portion. . Therefore, the gas sensor can be more effectively prevented from generating cracks in the detection element body.

The “reduced diameter portion” of the porous protective layer is a form in which the thickness is gradually reduced toward the proximal end side. Specifically, a taper shape, an R shape, or the like that gradually decreases in thickness toward the base end side can be given.
The “covering portion” of the porous protective layer covers the periphery of the detection element body from the tip of the detection element body to the reduced diameter portion. Further, the “protector” may be a protector having a multiple structure in which two or more protectors are overlapped, in addition to a protector having only a single structure. In the case of this multiple structure, the protector that is arranged on the innermost side and directly surrounds the detection element main body corresponds to the “protector” in the claims.

  Further, in the above gas sensor, it is preferable that the axial direction length of the reduced diameter portion of the porous protective layer is a gas sensor having a thickness not less than 3 mm and not more than 3 mm.

  In the gas sensor of the present invention, since the length in the axial direction of the reduced diameter portion is not less than the thickness of the covering portion and not more than 3 mm, it is possible to more reliably prevent the reduced diameter portion from being chipped due to vibration or impact during use. Therefore, it is possible to provide a highly reliable gas sensor that more effectively prevents the detection element body from being cracked.

  Furthermore, the gas sensor according to any one of the above, wherein the thickness of the covering portion is 100 μm or more and 600 μm or less.

  If the thickness of the covering portion of the porous protective layer is too thin, specifically less than 100 μm, the occurrence of cracks in the detection element body due to thermal shock when water droplets adhere to the porous protective layer, etc. There is a possibility that the effect originally required for the porous protective layer cannot be sufficiently obtained. On the other hand, if the thickness of the covering portion of the porous protective layer is too thick, specifically, if it is thicker than 600 μm, for example, heat is transferred to the porous protective layer when the temperature is raised by the heater. In some cases, the time until the activation of the gas sensor decreases and the activation time increases, the power consumption of the heater increases, and the detection sensitivity of the gas sensor deteriorates.

  On the other hand, in the gas sensor of the present invention, since the thickness of the covering portion of the porous protective layer is 100 μm or more, sufficient effects as a porous protective layer such as preventing the occurrence of cracks due to adhesion of water droplets are sufficiently obtained. be able to. On the other hand, since the thickness of the covering portion of the porous protective layer is 600 μm or less, it is possible to sufficiently shorten the time until the detection element is activated when the temperature is raised by the heater, and to reduce the power consumption of the heater. In addition, the detection sensitivity of the gas sensor is improved.

  Furthermore, in the gas sensor according to any one of the above, the covering portion may be a gas sensor that gently covers the element protruding portion of the detection element body.

  In the gas sensor of the present invention, the covering portion of the porous protective layer gently covers the element protruding portion of the detection element body. That is, since the detection element main body has a plate shape, the element projecting portion includes a main surface (plate surface) and a side surface, a main surface and a front end surface, a ridge (side) formed by the side surface and the front end surface, and three surfaces. The covering portion of the porous protective layer covering the element protruding portion has a gentle shape with no sharp corners on the entire outer surface. For this reason, it is possible to effectively prevent the covering portion from being chipped due to vibration or impact during use. Therefore, a more reliable gas sensor can be obtained.

  Furthermore, in the gas sensor according to any one of the above, a gas sensor in which a minimum gap between the covering portion and the protector is 0.5 mm or more is preferable.

If the minimum gap between the cover and the protector is too small, specifically less than 0.5 mm, water droplets that have entered the protector together with the gas to be measured are covered between the protector and the cover. Gently adhere to the part. In addition, water drops once attached to the inner peripheral surface of the protector may move on the inner peripheral surface and adhere to the covering portion.
On the other hand, in the present invention, since the minimum gap between the detection element and the protector is 0.5 mm or more, even if water droplets enter the protector together with the gas to be measured, it is difficult to adhere to the covering portion. Moreover, even if the water droplet adhering to the inner peripheral surface of the protector once moves, it becomes difficult to contact the covering portion. Therefore, it is possible to more reliably prevent the detection element body from being cracked by a thermal shock when a water droplet is attached.

  Furthermore, in the gas sensor according to any one of the above, the reduced diameter portion may be a gas sensor disposed inside the metal shell.

  In the gas sensor of the present invention, the reduced diameter portion is disposed inside the metal shell. Thereby, a metal shell becomes a barrier and a water droplet does not adhere easily to a reduced diameter part. Therefore, the gas sensor can be more effectively prevented from generating cracks in the detection element body.

  Furthermore, the gas sensor according to any one of the above, wherein the minimum clearance between the metal shell and the covering portion is 1.45 mm or less.

If the minimum gap between the metal shell and the cover is too large, specifically, greater than 1.45 mm, water droplets that have entered the protector together with the gas to be measured are formed between the metal shell and the detection element body (reduced diameter portion). It becomes easy to enter the gap, and water droplets easily adhere to the reduced diameter portion.
On the other hand, in the present invention, since the minimum gap between the metal shell and the covering portion is 1.45 mm or less, even if water droplets enter the protector together with the gas to be measured, it is difficult to adhere to the reduced diameter portion. Therefore, it is possible to more reliably prevent the detection element body from being cracked by a thermal shock when a water droplet is attached.

  Furthermore, in the gas sensor according to any one of the above, the distance between the reduced diameter portion and the tip of the metallic shell is preferably a gas sensor that is larger than a minimum gap between the metallic shell and the covering portion. Thereby, even if a water droplet enters into the protector together with the gas to be measured, it is more difficult to adhere to the reduced diameter portion. Therefore, it is possible to more reliably prevent the detection element body from being cracked by a thermal shock when a water droplet is attached. Furthermore, in the gas sensor according to any one of the above, it is further preferable that a minimum clearance between the metal shell and the covering portion is a gas sensor smaller than a diameter of the introduction hole.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a gas sensor 100 according to this embodiment. 2 and 3 are enlarged views of the front end portion of the gas sensor 100. FIG. Further, FIG. 4 shows a plan view of the tip side portion of the detection element 200 constituting the gas sensor 100. FIG. 5 is an exploded perspective view of the detection element main body 201 of the detection element 200. FIG. 6 shows a cross-sectional view (A-A cross-sectional view in FIG. 4) of the tip side portion of the detection element 200. 1 to 4, the lower side in the drawings is the distal end side in the axis AX direction (hereinafter, also simply referred to as the distal end side), and the upper side in the drawings is the proximal end side in the axis AX direction (hereinafter referred to as “the distal end side”). It is also simply referred to as the base end side). In FIG. 5, the left side is the distal end side, and the right side is the proximal end side in the figure.

  This gas sensor 100 is attached to an exhaust pipe of an automobile (not shown), and a detection element 200 held inside is exposed to exhaust gas (detected gas) flowing through the exhaust pipe, so that oxygen (specific gas) in the exhaust gas is exposed. This is a so-called full-range air-fuel ratio sensor that detects the air-fuel ratio of exhaust gas from the concentration of the component. As shown in FIG. 1, the gas sensor 100 includes a cylindrical metal shell 110 extending in the direction of the axis AX, a plate-shaped detection element 200 held inside the metal shell 110, and a base end side of the metal shell 110. The outer cylinder 151 is provided, the protector 160 is fixed to the front end side of the metal shell 110, and the like.

  Among these, the detection element 200 has a fixed width H (4 mm) and thickness D (1.5 mm) (see FIG. 6), and has a plate shape (strip shape) extending in the axis AX direction. A main body 201 is provided. The detection element body 201 includes a first plate surface 201a, a second plate surface 201b, a first side surface 201c, and a second side surface 201d (see FIGS. 4 and 6). As shown in FIG. 1, the detection element main body 201 includes an element protruding portion 202 that protrudes from a distal end side open end 110s of a metal shell 110, which will be described later, to the front end side (downward in the drawing), and a radial direction around the metal shell 110. And a device base end portion 209 that protrudes from the metal shell 110 to the base end side (upward in the figure).

  A metal metal cup 131 having a bottomed cylindrical shape is inserted into the inner side of the detection element 200 at the front end side slightly from the center of the body portion 207 of the detection element 200, and the front end side portion is opened at the bottom of the cylinder bottom. It is arranged in a state of protruding from 131c. The metal cup 131 is a member for holding the detection element 200 in the metal shell 110, and the distal end peripheral portion 132 is formed in a tapered shape having a diameter reduced toward the distal end side. In the metal cup 131, an alumina ceramic ring 133 and a first talc ring 135 compressed with talc powder are accommodated in a state where the detection element 200 is inserted. The first talc ring 135 is crushed in the metal cup 131 and filled to the fine details, whereby the detection element 200 is positioned and held in the metal cup 131.

  The detection element 200 integrated with the metal cup 131 is held by being surrounded by a cylindrical metal shell 110 around its radial direction. The metal shell 110 is for attaching and fixing the gas sensor 100 to the exhaust pipe of the automobile, and is made of SUS430 low carbon steel. A male screw portion 111 for attachment to the exhaust pipe is formed on the outer peripheral tip side of the metal shell 110. Further, an annular tip fixing portion 113 to which a protector 160 (described later) is fixed is formed protruding from the tip side of the male screw portion 111.

  A tool engaging portion 117 with which a tool for attachment is engaged is formed at the center of the outer periphery of the metal shell 110. In addition, a gasket 119 is inserted between the tool engagement portion 117 and the male screw portion 111 in the metal shell 110 to prevent gas from being released when the metal fitting 110 is attached to the exhaust pipe. Further, a base end fixing portion 116 to which an outer cylinder 151 described later is fixed is formed on the base end side of the tool engaging portion 117. Further, a caulking portion 118 for caulking and holding the detection element 200 in the metal shell 110 is formed on the base end side.

  Further, on the inner peripheral front end side of the metal shell 110, a stepped portion 115 having a tapered shape whose diameter decreases toward the front end side is formed. The stepped portion 115 is engaged with a tip peripheral portion 132 having a tapered shape of the metal cup 131 that holds the detection element 200. Further, a second talc ring 137 is disposed in a state where the detection element 200 is inserted on the proximal end side of the metal cup 131 inside the metal shell 110. A cylindrical sleeve 141 is fitted into the metal shell 110 so that the second talc ring 137 is pressed from the base end side. The sleeve 141 is formed with a shoulder 142 having a stepped shape. An annular caulking packing 143 is disposed on the shoulder 142. The caulking portion 118 of the metal shell 110 is caulked so as to press the shoulder 142 of the sleeve 141 toward the distal end side through the caulking packing 143.

  The second talc ring 137 pressed against the sleeve 141 is crushed in the metal shell 110 and filled in details, and the second talc ring 137 and the first talc ring 135 preloaded in the metal cup 131, Thus, the metal cup 131 and the detection element 200 are positioned and held in the metal shell 110. The airtightness in the metal shell 110 is maintained by the caulking packing 143 interposed between the caulking portion 118 and the shoulder portion 142 of the sleeve 141, and the outflow of combustion gas is prevented.

  The element base end 209 of the detection element 200 protrudes to the base end side with respect to the crimping portion 118 that is the base end of the metal shell 110, and the element base end 209 has a cylinder made of insulating ceramics. -Shaped separator 145 is covered. The separator 145 has five connection terminals 147, 147,... That are electrically connected to the five electrode pads 235, 235,... Formed on the element base end portion 209 of the detection element 200, respectively (in FIG. One is shown.) Is held inside. These connection terminals 147, 147, ... are also electrically connected to five lead wires 149, 149, ... (three of which are shown in Fig. 1) drawn out of the gas sensor 100. ing. The separator 145 accommodates the connection portions of the connection terminals 147, 147,... And the lead wires 149, 149,.

  A cylindrical outer cylinder 151 is disposed so as to surround the separator 145. The outer cylinder 151 is made of stainless steel (SUS304 in this embodiment), and the distal end opening 152 is disposed on the radially outer side of the proximal end fixing portion 116 of the metal shell 110. The distal end opening 152 is crimped from the outside, and is further laser-welded around the outer periphery and joined to the proximal end fixing portion 116.

  In addition, in the gap between the outer cylinder 151 and the separator 145, a metal-made holding metal fitting 153 is disposed. The holding metal fitting 153 has a support portion 154 formed by bending its own base end inward, and a hook portion 146 provided in a hook shape on the outer periphery of the base end side of the separator 145 inserted into the inside thereof. The separator 145 is supported by being engaged with the support portion 154. In this state, the outer cylinder 151 at the portion where the holding metal fitting 153 is disposed is crimped from the outside, and the holding metal fitting 153 supporting the separator 145 is fixed to the outer cylinder 151.

  Further, a fluoro rubber grommet 155 is fitted into the base end side opening of the outer cylinder 141. This grommet 155 has five insertion holes 156, 156,... (One of which is shown in FIG. 1), and 5 extending from the separator 145 to each insertion hole 156, 156,. The lead wires 149, 149,... Are inserted in an airtight manner. In this state, the grommet 155 is fixed to the outer cylinder 151 by being crimped from the outside of the outer cylinder 151 while pressing the separator 145 toward the distal end.

  The detection element 200 held by the metal shell 110 has an element protruding portion 202 that protrudes to the front end side from the front end opening end 110 s of the metal shell 110. The tip fixing portion 113 protects the element protruding portion 202 of the detection element 200 from contamination due to deposits (toxic substances such as fuel ash and oil components) in the exhaust gas, breakage due to moisture, and the like. A protector 160 is fitted and fixed by laser welding. The protector 160 has a double structure including a bottomed cylindrical inner protector 161 and a cylindrical outer protector 171 surrounding the inner periphery of the inner protector 161 via a gap.

  The inner protector 161 has a bottomed cylindrical shape, surrounds the tip end side (downward in the figure) and the radially outer side (leftward and rightward direction in the figure) of the element protruding portion 202 of the detection element 200, and projects the element inside itself. It is fixed to the metallic shell 110 with the portion 202 disposed. In this inner protector 161, inner introduction holes 167, 167,... For introducing exhaust gas from the outside to the inside are provided at the base end from the tip 200s of the detection element 200 (the tip side end 240s of the porous protective layer 240). A plurality are provided on the side. In the present embodiment, the inner introduction hole 167 has a diameter of 1.5 mm. The inner introduction hole corresponds to the “introduction hole” in the claims. Further, a plurality of drain holes 166, 166,... Opened in a cut shape toward the inside are provided on the front end side of the inner protector 161. These drain holes 166, 166,... Are formed on the tip side of the tip 200s of the detection element 200. A discharge hole 164 for discharging exhaust gas and water to the outside is formed in the center of the bottom wall of the inner protector 161.

  On the other hand, the outer protector 171 is fixed to the metal shell 110 in a state in which the outer periphery of the inner protector 161 is surrounded by a gap. The front end 172 of the outer protector 171 is bent inward toward the inner protector 161. Thereby, the space | gap of the inner side protector 161 and the outer side protector 171 is obstruct | occluded by the front end side. Further, in the outer protector 171, a plurality of outer introduction holes 177, 177,... For introducing exhaust gas from the outside to the inside are provided in the circumferential direction at a predetermined position on the tip side of the tip 200s of the detection element 200. It is formed side by side. Each of these outer introduction holes 177, 177,... Is provided with a plate-shaped guide body 178, 178,. As a result, the exhaust gas introduced from the outside through the outer introduction holes 177, 177,... Generates a swirling flow that swirls in the circumferential direction of the axis AX in the gap with the inner protector 161.

Next, the detection element 200 which is a main part of the present invention will be described. A porous protective layer 240 made of porous alumina is coated on the entire element protruding portion 202 of the detection element 200 and a part on the front end side of the body portion 207 so as to cover the outer surface thereof.
In the porous protective layer 240, the base end side (upward in the drawing) is within a range where the length tk (see FIG. 4) in the axis AX direction from the base end 240k is 3 mm or less (1 mm in this embodiment). A diameter-reduced portion 247 is provided that gradually decreases in thickness toward. In the present embodiment, the reduced diameter portion 247 has a tapered shape with a thickness that decreases in proportion to the distance in the direction of the axis AX. Further, the reduced diameter portion 247 is disposed 3 mm (corresponding to the distance I in FIG. 3) behind the distal end opening end 110 s of the metal shell 110. This corresponds to the distance I being larger than the minimum gap H between the metal shell 110 and the covering portion 242 (base end side covering portion 243) described later.

  Moreover, the coating | coated part 242 is provided in the front end side rather than the diameter reducing part 247 among the porous protective layers 240 (refer FIG.2 and FIG.3). Among these, the portion covering the entire element protruding portion 202 on the distal end side of the distal end side open end 110 s of the metal shell 110 is the distal end side covering portion 241, and a part of the front end side of the trunk portion 207 is formed in the metal shell 110. A portion to be covered is the base end side covering portion 243. Therefore, the front end side covering portion 241 protrudes from the front end side opening end 110s of the metal shell 110 to the front end side. On the other hand, the base end side covering portion 243 is located closer to the base end side than the distal end side opening end 110s.

The front end side covering portion 241 gently covers the element protruding portion 202 of the detection element main body 201, and the outer surface thereof has a shape without a sharp corner (see FIGS. 2 to 4 and 6). . That is, the corner portions 245, 245,... Of the tip side covering portion 241 are all rounded.
Moreover, the thickness dk (refer FIG.4 and FIG.6) of the coating | coated part 242 among the porous protective layers 240 shall be 100 micrometers or more and 600 micrometers or less (400 micrometers in this embodiment). The minimum gap G (see FIG. 3) between the porous protective layer 240 and the inner protector 161 is 0.5 mm or more (1 mm in this embodiment). Furthermore, the minimum gap H (see FIG. 3) between the porous protective layer 240 (rear end side covering portion 243) and the metallic shell 110 is 1.45 mm or less (in this embodiment, 1.25 mm). This is smaller than the diameter of the inner introduction hole 167 of the inner protector 161.

  As shown in FIGS. 5 and 6, the detection element main body 201 is formed by simultaneously firing a plurality of layers stacked on each other, and includes a sensor function unit 250 that functions to detect a specific gas component, and the sensor. A protective unit 260 that is stacked on one side of the functional unit 250 and protects the sensor functional unit 250, and a heater unit 270 that is stacked on the other side of the sensor functional unit 250 and that heats to activate the sensor functional unit 250 early. Have

Among these, the sensor function part 250 is comprised from the oxygen pump cell 251, the oxygen concentration detection cell 253, and the insulating layer 219 laminated | stacked among these.
The oxygen pump cell 251 includes a first solid electrolyte layer 215 and a first electrode 213 and a second electrode 217 formed on both surfaces of the first solid electrolyte body 215. The first solid electrolyte layer 215 is composed of a partially stabilized zirconia sintered body having zirconia as a main component and yttria or calcia added to a stabilizer. A first through-hole conductor 215a and a second through-hole conductor 215b are formed to penetrate at a predetermined position on the base end side of the first solid electrolyte layer 215.

The first electrode 213 is mainly composed of platinum, and has a first electrode portion 213a having a rectangular shape in plan view formed at a predetermined position on the distal end side, and a first lead portion extending from the first electrode portion 213a toward the proximal end side. 213b. The first lead portion 213b is electrically connected at its proximal end to an eighth through-hole conductor 211c provided in a protective main body layer 211 described later.
The second electrode 217 is also mainly composed of platinum, and has a second electrode portion 217a having a rectangular shape in plan view formed at a predetermined position on the distal end side, and a second lead portion extending from the second electrode portion 217a toward the proximal end side. 217b. The second lead portion 217b is electrically connected to the second through-hole conductor 215b provided in the first solid electrolyte layer 215 at the base end thereof, and is a fifth through-hole provided in an insulating layer 219 described later. It is electrically connected to the conductor 219b.

  The oxygen concentration detection cell 253 includes a second solid electrolyte layer 223 and a third electrode 221 and a fourth electrode 225 formed on both surfaces of the second solid electrolyte layer 223. Similar to the first solid electrolyte layer 215, the second solid electrolyte layer 223 is composed of a partially stabilized zirconia sintered body having zirconia as a main component and yttria or calcia added to a stabilizer. Further, a third through-hole conductor 223a is formed to penetrate at a predetermined position on the base end side of the second solid electrolyte layer 223.

The third electrode 221 is mainly composed of platinum, and has a third electrode portion 221a having a rectangular shape in plan view formed at a predetermined position on the distal end side, and a third lead portion extending from the third electrode portion 221a toward the proximal end side. 221b. The third lead portion 221b is electrically connected to a fifth through-hole conductor 219b provided in an insulating layer 219 described later at the base end thereof.
The fourth electrode 225 is also mainly composed of platinum, and has a fourth electrode portion 225a having a rectangular shape in plan view formed at a predetermined position on the distal end side, and a fourth lead portion extending from the fourth electrode portion 225a to the proximal end side. 225b. The fourth lead portion 225b is electrically connected to the second through-hole conductor 223a provided in the second solid electrolyte layer 223 at the base end.

  The insulating layer 219 is formed using alumina as a main component. The insulating layer 219 is provided with a gas detection chamber 219d having a rectangular shape in plan view that penetrates the insulating layer 219 at a position corresponding to the second electrode portion 217a and the third electrode portion 221a. In addition, on both sides of the gas detection chamber 219d in the width direction, diffusion rate controlling portions 220 and 220 for realizing gas diffusion between the outside of the element and the gas detection chamber 219d under predetermined rate limiting conditions are provided. The diffusion control parts 220 and 220 are made of a porous body of alumina.

  Further, a fourth through-hole conductor 219a and a fifth through-hole conductor 219b are formed to penetrate at a predetermined position on the base end side of the insulating layer 219. The fourth through-hole conductor 219a is electrically connected to the first through-hole conductor 215a provided in the first solid electrolyte layer 215, and is connected to the third through-hole conductor 223a provided in the second solid electrolyte layer 223. Electrically connected. The fifth through-hole conductor 219b is electrically connected to the second lead portion 217b of the second electrode 217 and electrically connected to the third lead portion 221b of the third electrode 221.

  Next, the protection unit 260 will be described. The protective part 260 has a protective main body layer 211 mainly composed of alumina. The protective body layer 211 is provided with an opening 211d having a rectangular shape in plan view that penetrates the protective body layer 211 at a position corresponding to the first electrode portion 213a. And in this opening 211d, the porous gas introducing | transducing part 212 which has an alumina as a main component is provided so that this may be obstruct | occluded.

  In addition, three electrode pads 235, 235, and 235 are arranged side by side in a width direction at a predetermined position on the base end side of the surface of the protective main body layer 211. Further, a sixth through-hole conductor 211a, a seventh through-hole conductor 211b, and an eighth through-hole conductor 211c are formed through the protective body layer 211 at a predetermined position on the base end side. The sixth through-hole conductor 211a is electrically connected to one of the electrode pads 235 and is electrically connected to the first through-hole conductor 215a provided in the first solid electrolyte layer 215. The seventh through-hole conductor 211b is electrically connected to one of the electrode pads 235 and is also electrically connected to the second through-hole conductor 215b provided in the first solid electrolyte layer 215. The eighth through-hole conductor 211c is electrically connected to one of the electrode pads 235 and is electrically connected to the first lead portion 213b of the first electrode 213.

  Next, the heater unit 270 will be described. The heater unit 270 includes an electrically insulating first heater insulating layer 227, an electrically insulating second heater insulating layer 231, and a heating resistor 229 that is sandwiched between them and generates heat when energized. The first heater insulating layer 227 is formed with alumina as a main component and is stacked on the sensor function unit 250. The second heater insulating layer 231 is also formed with alumina as a main component.

  In addition, a ninth through-hole conductor 231a and a tenth through-hole conductor 231b are formed penetratingly at a predetermined position on the base end side of the second heater insulating layer 231. In addition, two electrode pads 235 and 235 are arranged side by side in the width direction at a predetermined position on the base end side of the surface of the second heater insulating layer 231. One electrode pad 235 is electrically connected to the ninth through-hole conductor 231a. The other electrode pad 235 is electrically connected to the tenth through-hole conductor 231b.

  The heat generating resistor 229 is disposed at a predetermined position on the distal end side, and has a meandering heat generating portion 229a, a first heater lead portion 229b extending from one end of the heat generating portion 229a to the base end side, and the other end of the heat generating portion 229a. And a second heater lead portion 229c extending from the base end side to the base end side. The first heater lead portion 229b is electrically connected to the ninth through-hole conductor 231a provided in the second heater insulating layer 231 at the base end. The second heater lead portion 229c is electrically connected to the tenth through-hole conductor 231b provided in the second heater insulating layer 231 at the base end.

Next, a method for manufacturing the gas sensor 100 and the detection element 200 will be described. In addition, the member after baking and the member before baking corresponding to this are demonstrated using the same code | symbol for convenience (refer FIG.5 and FIG.6).
First, a slurry was prepared in which a first raw material powder composed of 97 wt% alumina powder and 3 wt% silica as a sintering regulator and a plasticizer composed of butyral resin and dibutyl phthalate (DBP) were dispersed by wet mixing. Then, this slurry is formed into a sheet-like material by a sheet forming method using a doctor blade device, and then cut into a predetermined size to form an unfired insulating layer 219 corresponding to the insulating layer 219 and the protective main body layer 211. A corresponding unfired protective main body layer 211, an unfired first heater insulating layer 227 corresponding to the first heater insulating layer 227, and an unfired second heater insulating layer 231 corresponding to the second heater insulating layer 231 were formed, respectively. . Further, a gas detection chamber 219d was formed in the unfired insulating layer 219. In addition, an opening 211 d was formed in the unfired protective main body layer 211.

On the other hand, a slurry was prepared in which a second raw material powder consisting of 63 wt% alumina powder, 3 wt% silica as a sintering regulator and 34 wt% carbon powder, and a plasticizer consisting of butyral resin and DBP were dispersed by wet mixing. . And using this slurry, the unfired gas introduction part 212 corresponding to the gas introduction part 212 was obtained.
Further, a slurry was prepared in which 100 wt% of alumina powder and a plasticizer composed of butyral resin and DBP were dispersed by wet mixing. And using this slurry, the unsintered diffusion rate limiting portions 220 and 220 corresponding to the diffusion rate limiting portions 220 and 220 were obtained.

  Further, a slurry in which a third raw material powder composed of 97 wt% of zirconia powder and silica as a sintering regulator (a total of 3 wt% of SiO2 powder and alumina powder) and a plasticizer composed of butyral resin and DBP are dispersed by wet mixing is used. Prepared. Then, an unfired first solid electrolyte body 215 corresponding to the first solid electrolyte body 215 and an unfired second solid electrolyte body 223 corresponding to the second solid electrolyte body 223 were formed using this slurry.

  Then, in order from the lower side shown in FIG. 5, the unfired second heater insulating layer 231, the unfired heating resistor 229 corresponding to the heating resistor 229, the unfired first heater insulating layer 227, and the fourth electrode 225. Unsintered fourth electrode 225, unsintered second solid electrolyte layer 223, unsintered third electrode 221 corresponding to third electrode 221, unsintered insulating layer 219, unsintered second corresponding to second electrode 217 The electrode 217, the unfired first solid electrolyte layer 215, the unfired first electrode 213 corresponding to the first electrode 213, the unfired protective main body layer 211, and the like were laminated to form an unfired laminate.

Specifically, an unfired heating resistor 229 was formed on the unfired second heater insulating layer 231 by screen printing using a paste mainly composed of platinum. Then, an unfired first heater insulating layer 227 was laminated on the unfired second heater insulating layer 231 and the unfired heating resistor 229.
Further, an unfired fourth electrode 225 was formed on one surface of the unfired second solid electrolyte layer 223 by clean printing using a platinum paste of 90 wt% platinum and 10 wt% zirconia powder. And these were laminated | stacked on the unbaked 1st heater insulating layer 227 so that the unbaked 4th electrode 225 might be pinched | interposed. Thereafter, an unfired third electrode 221 was formed on the unfired second solid electrolyte layer 223 by clean printing using a platinum paste of 90 wt% platinum and 10 wt% zirconia powder.

Next, the unsintered insulating layer 219 and the unsintered diffusion limiting parts 220 and 220 were laminated on the unsintered second solid electrolyte layer 223 and the unsintered third electrode 221. In addition, after baking, the paste which has carbon as a main component is printed in the part used as the gas detection chamber 107c.
Further, an unfired second electrode 217 was formed on one surface of the unfired first solid electrolyte layer 215 by clean printing using a platinum paste of 90 wt% platinum and 10 wt% zirconia powder. And these were laminated | stacked on the unbaking insulating layer 219 so that the unbaking 2nd electrode 217 might be pinched | interposed. Thereafter, an unfired first electrode 213 was formed on the unfired first solid electrolyte layer 215 by clean printing using a platinum paste of 90 wt% platinum and 10 wt% zirconia powder.
Next, an unfired protective main body layer 211 was laminated on the unfired first solid electrolyte layer 215 and the unfired first electrode 213. An unsintered gas introduction part 212 corresponding to the gas introduction part 212 is formed in the unsintered protection main body layer 211 in advance. Thus, an unfired laminate is formed.

  Next, this unfired laminate was pressed and pressure-bonded at 1 MPa, and then cut into a predetermined size. Thereafter, the unfired laminate was removed from the resin, and further subjected to main firing which was held at a firing temperature of 1500 ° C. for 1 hour, whereby a detection element body 201 was obtained.

  Next, spinel powder and titania powder were prepared, and ethanol as a volatile solvent was further added to prepare a coating solution. Then, as shown in FIGS. 7 and 8, this coating liquid was sprayed on the detection element main body 201 to form an unfired porous protective layer 240 that becomes the porous protective layer 240 after firing, and was dried.

  Specifically, first, as shown in FIG. 7, in a state where the element protruding portion 202 of the detection element body 201 is protruded by the first holding jig 300, the base end side portion (body portion) of the detection element body 201 is formed. 207 and element base end portion 209). And the coating liquid was made to adhere to the element protrusion part 202 of the detection element main body 201 from the front end side of the detection element main body 201 with the spray apparatus 320 using the needle type nozzle. At that time, the suction device 330 is arranged on the outer side in the radial direction of the detection element main body 201, and the ceramic powder (the one in which ethanol is volatilized from the coating liquid) scattered around is collected. The ceramic powder recovered by the suction device 330 is reused by being dispersed again in ethanol.

  Next, the detection element body 201 was removed from the first holding jig 300. Next, as shown in FIG. 8, the element projecting portion 202 of the detection element main body 201 and the body front end side portion 207 a that is a part of the front end side of the body portion 207 are protruded by the second holding jig 310. In the state, the base end side portions of the detection element main body 201 (the trunk base end side portion 207b and the element base end portion 209 which are the remaining portions of the trunk portion 207) were held. This 2nd holding jig 310 has the protrusion part 311 which comprises the mortar-shaped recessed part 313 in the front-end | tip. Then, by rotating the second holding jig 310 about the axis, the spray device 320 coats the detection element body 201 from the outside in the radial direction of the detection element body 201 while rotating the detection element body 201 around the axis. The liquid was applied. Since the volatile solvent is volatilized when the coating liquid adheres to the surface of the detection element body 201, a layer of the dried ceramic raw material powder is formed on the surface of the detection element body 201 (the element protruding portion 202 and the body front end side portion 207a). It is formed.

  At this time, since the second holding jig 310 is provided with the protruding portion 311, the protruding portion 311 serves as a barrier, and the second holding jig out of the body distal end side portion 207 a of the detection element body 201. The amount of the coating liquid to be deposited on the proximal end portion in the vicinity of the tool 310 decreases as it goes toward the proximal end. This portion becomes the reduced diameter portion 247 after firing.

  Next, the detection element body 201 in this state is heated in an air atmosphere, heat-treated while being held at a maximum temperature of 1000 ° C. for 1 hour, and then cooled by air to have a porous protective layer 240. The detection element 200 was obtained.

  Then, the detection element 200 manufactured by the above-described method is inserted into the metal cup 131 and further fixed by the ceramic ring 133 and the first talc ring 135 to form an assembly. Thereafter, the assembly is inserted into the metal shell 110 to which the protector 160 is joined, and the second talc ring 137, the sleeve 141, and the caulking packing 143 are further inserted, and the caulking portion 118 of the metal shell 110 is caulked. Forming a lower assembly; On the other hand, the outer cylinder 151, the separator 141, the grommet 155, and the like are assembled to form an upper assembly. Then, the lower assembly and the upper assembly are joined to complete the gas sensor 100.

  As described above, in the present embodiment, the diameter-reduced portion 247 of the porous protective layer 240 is tapered so that the thickness gradually decreases toward the base end side. There are no sharp corners. For this reason, it is possible to prevent the reduced-diameter portion 247 from being chipped due to vibration or impact during use, and the porous protective layer 240 in this portion can be prevented from being thinned, or the detection element body 201 can be prevented from being exposed in this portion. Even if the water droplet inside adheres to the reduced diameter portion 247, the detection element body 201 is unlikely to crack. In addition, since the reduced diameter portion 247 is disposed on the proximal end side with respect to the inner introduction hole 167 of the inner protector 161 that directly surrounds the porous protective layer 240, water drops that have passed through the inner introduction hole 167 are reduced in diameter. It is difficult to adhere to 247. Therefore, the gas sensor 100 can be obtained in which cracks in the detection element body 201 are more effectively prevented.

Further, since the length tk in the axis AX direction of the reduced diameter portion 247 of the porous protective layer 240 is set to the thickness dk of the covering portion 242 and 3 mm or less, the reduced diameter portion 247 is not chipped due to vibration or impact during use. It can prevent more reliably.
In addition, since the thickness dk of the covering portion 242 of the porous protective layer 240 is 100 μm or more, the effects as the porous protective layer 240 such as prevention of generation of cracks due to adhesion of water droplets can be sufficiently obtained. On the other hand, since the thickness dk of the covering portion 242 of the porous protective layer 240 is 600 μm or less, it is possible to sufficiently shorten the time until the detection element 200 is activated when the heating resistor 229 raises the temperature. The power consumption can be reduced. In addition, the detection sensitivity of the detection element 200 is improved.

Further, the covering portion 242 of the porous protective layer 240 gently covers the element protruding portion 202 of the detection element main body 201. For this reason, it is possible to prevent the covering portion 242 from being chipped due to vibration or impact during use.
In the present embodiment, since the minimum gap G between the covering portion 242 and the inner protector 161 is 0.5 mm or more, even if water droplets enter the inner protector 161 together with the gas to be detected, they adhere to the covering portion 242. It becomes difficult. Further, it is possible to prevent water droplets once attached to the inner peripheral surface of the inner protector 161 from coming into contact with the covering portion 242. Therefore, it is possible to more reliably prevent the detection element 200 from being cracked by a thermal shock when a water droplet adheres.

Further, the reduced diameter portion 247 is disposed inside the metal shell 110. Thereby, the metal shell 110 serves as a barrier, and water droplets hardly adhere to the reduced diameter portion 247. Therefore, the gas sensor 100 can be obtained in which cracks in the detection element body 201 are more effectively prevented.
Furthermore, since the minimum gap H between the metal shell 110 and the covering portion 242 is 1.45 mm or less, even if water droplets enter the inner protector 161 together with the gas to be measured, it is difficult to adhere to the reduced diameter portion 247. Therefore, it is possible to more reliably prevent the detection element body 201 from being cracked by a thermal shock when a water droplet is attached.
Further, since the distance I between the distal end side opening end 110 s of the metal shell 110 and the reduced diameter portion 247 is larger than the minimum gap H between the metal shell 110 and the covering portion 242, water droplets together with the gas to be measured enter the inner protector 161. Even if it enters, it becomes more difficult to adhere to the reduced diameter portion 247. Therefore, it is possible to more reliably prevent the detection element body 201 from being cracked by a thermal shock when a water droplet is attached. Furthermore, even if the minimum gap H between the metal shell 110 and the covering portion 247 is smaller than the diameter of the inner introduction hole 167, water droplets are less likely to adhere to the reduced diameter portion 247, and a crack occurs in the detection element body 201. Can be prevented.

In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof. .
For example, in the above-described embodiment, the full-range air-fuel ratio sensor is exemplified as the gas sensor 100, but the present invention can also be applied to an oxygen sensor, a NOx sensor, an HC sensor, and the like.
Moreover, in the said embodiment, although the protector 160 was illustrated by the double structure of the inner side protector 161 and the outer side protector 171, the protector of a single structure may be sufficient.
In the above embodiment, the covering portion 242 includes the distal end side covering portion 241 that covers the entire element protruding portion 202, and the proximal end side covering portion 243 that covers a part of the front end side of the body portion 207 within the metal shell 110. Although the structure is exemplified, the reduced diameter portion 247 is exposed to the front end side from the front end opening end 110s of the metal shell 110, and the cover portion 242 includes only the front end side covering portion 241 that covers a part of the element protruding portion 202. It may be. In this case, the reduced diameter portion 247 is disposed closer to the proximal end than the inner introduction hole 167 of the inner protector 161.

It is a fragmentary sectional view of the gas sensor concerning an embodiment. It is sectional drawing seen from the side surface side of a detection element among the front end side parts of the gas sensor which concerns on embodiment. It is sectional drawing seen from the plate | board surface side of the detection element among the front end side parts of the gas sensor which concerns on embodiment. It is a top view of the front end side part of a detection element among the gas sensors which concern on embodiment. It is a disassembled perspective view of the detection element main body of a detection element among the gas sensors which concern on embodiment. It is a cross-sectional view (AA sectional drawing of FIG. 4) of the front end side part of a detection element among the gas sensors which concern on embodiment. It is explanatory drawing which shows a mode that a coating liquid is sprayed to a detection element main body from the front end side in order to form a non-baking porous protective layer regarding the manufacturing method of the gas sensor which concerns on embodiment. It is explanatory drawing which shows a mode that a coating liquid is sprayed from the radial direction outer side to a detection element main body in order to form a non-baking porous protective layer regarding the manufacturing method of the gas sensor which concerns on embodiment.

Explanation of symbols

100 gas sensor 110 metal shell 110s front end opening end 160 protector 161 inner protector 171 outer protector 200 detecting element 201 detecting element body 201a first plate surface 201b second plate surface 201c first side surface 202d second side surface 202 element protruding portion 207 trunk 209 Element base end portion 240 Porous protective layer 240s Tip side end 240k Base end side end 241 Tip side cover portion 243 Base end side cover portion 245 Corner portion 247 (tip end side cover portion) Protective layer base end portion AX Axis

Claims (9)

A cylindrical metal shell extending in the axial direction;
A plate-shaped detection element main body having an element protruding portion protruding from the tip of the metal shell, extending in the axial direction, and held on the radially inner side of the metal shell;
A porous protective layer covering the tip side of the detection element body;
A protector which is attached to the metal shell so as to directly surround the porous protective layer, and is provided with an introduction hole for introducing the gas to be measured into a side wall disposed around the radial direction of the element protrusion. A gas sensor,
The porous protective layer is composed of a covering portion and a diameter-reduced portion that is provided closer to the base end side than the covering portion and gradually decreases in thickness toward the base end side,
The reduced diameter portion is a gas sensor arranged on the proximal end side from any of the introduction holes. The gas sensor according to claim 1,
The gas sensor in which the length in the axial direction of the reduced diameter portion of the porous protective layer is not less than the thickness of the covering portion and not more than 3 mm. The gas sensor according to claim 1 or 2, wherein
A gas sensor having a thickness of the covering portion of 100 μm or more and 600 μm or less. The gas sensor according to any one of claims 1 to 3,
The covering portion is a gas sensor that gently covers the element protruding portion. It is a gas sensor as described in any one of Claims 1-4, Comprising:
A gas sensor having a minimum gap of 0.5 mm or more between the covering portion and the protector. It is a gas sensor as described in any one of Claims 1-5, Comprising:
The reduced diameter portion is a gas sensor disposed inside the metal shell. The gas sensor according to claim 6,
A gas sensor in which a minimum gap between the metal shell and the covering portion is 1.45 mm or less. The gas sensor according to claim 6 or 7, wherein
A gas sensor in which a distance between the reduced diameter portion and a tip of the metal shell is larger than a minimum gap between the metal shell and the covering portion. The gas sensor according to claim 6 to 8, wherein
A gas sensor in which a minimum gap between the metal shell and the covering portion is smaller than a diameter of the introduction hole.