The present application claims priority to Japanese Patent Applications No. 2014-011385, filed on Jan. 24, 2014 and Japanese Patent Applications No. 2014-212197, filed on Oct. 17, 2014, the disclosures of which are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to a laminated gas sensor element, a gas sensor, and a method of manufacturing the gas sensor element.
2. Description of Related Art
An example of a known gas sensor for detecting a particular gas is an oxygen sensor including a cell which has a pair of electrodes disposed on the outer surface of a solid electrolyte body. An example of a known sensor element used in such a gas sensor is a laminated gas sensor element formed by laminating a plurality of plate-shaped members (below listed Patent Documents 1 and 2). In the conventional laminated gas sensor element, the solid electrolyte body is embedded in a through-hole formed in a flat plate-shaped insulating member, and has a rectangular contour shape.
Patent Document 1 is Japanese Patent No. 4050542.
Patent Document 2 is Japanese Patent No. 4669429.
However, since the solid electrolyte body whose contour shape is rectangular is dense, the conventional gas sensor element has a problem in that, when an external force or a stress such as thermal stress acts on the solid electrolyte body, stress concentration is likely to occur at the four corners thereof, and the solid electrolyte body breaks easily. Also, the conventional gas sensor element has a problem in that, when the solid electrolyte body is embedded in the through-hole of the insulating member, a gap is formed between the solid electrolyte body and the insulating member, and the gap serves a bypass passage for gas, which may result in deterioration of sensor performance.
The present invention has been accomplished in order to solve the above problem and can be embodied in the following modes.
(1) One mode of the present invention is a laminated gas sensor element comprising a plurality of laminated plate-shaped members, including a plate-shaped insulating member in which a solid electrolyte body is embedded and which has four sides. In the laminated gas sensor element, as viewed in a plane orthogonal to a thickness direction of the insulating member including the solid electrolyte body (i.e., a top or bottom plan view, where the front, rear, and side elevational views are views of each of the four sides of the plate-shaped insulating member), a portion of a contour of the solid electrolyte body has an arcuate shape projecting toward at least one side of the four sides. In other words, a portion of the contour of the solid electrolyte body, the portion facing at least one side of the four sides, forms an arcuate shape projecting toward the one side.
According to this mode, the solid electrolyte body has a contour which forms an arcuate shape projecting toward at least one side of the four sides of the insulating member. Therefore, when an external force or a stress such as thermal stress acts on the solid electrolyte body, stress concentration is less likely to occur, as compared with the case where the contour forms a rectangular shape as in the case of conventional gas sensor elements. Therefore, the laminated gas sensor element of the present mode does not break easily.
(2) In the above-described gas sensor element, a shape (the contour shape) of the solid electrolyte body is a circle, an ellipse, or a rectangle with rounded short sides (i.e., a rectangular shape where the short sides are arcuate or rounded).
According to this mode, stress concentration can be mitigated to a greater degree.
(3) In the above-described gas sensor element, a portion (another portion) of the contour of the solid electrolyte body has a shape of a longitudinally extending straight line facing a longitudinally extending side of the four sides. In other words, a portion of the contour of the solid electrolyte body, the portion facing a longitudinally extending side of the four sides, forms the shape of a longitudinally extending straight line.
According to this mode, the area of the solid electrolyte body can be made sufficiently large.
(4) Another mode of the present invention is a method of manufacturing the above-described gas sensor element (as described with reference to identifiers (1), (2), or (3)). The method comprises (a) a step of forming a green solid electrolyte layer formed of a green solid electrolyte material on a support sheet; (b) a step of removing, from the green solid electrolyte layer on the support sheet, (a portion of) the green solid electrolyte material, excluding a green solid electrolyte body which is to become the solid electrolyte body of the gas sensor element; (c) a step of transferring the green solid electrolyte body onto a green insulating layer formed of a green insulating material; and (d) a step of forming a green plate-shaped member in which the green solid electrolyte body is surrounded by the green insulating material by applying the green insulating material by means of printing on the green insulating layer in a region around the transferred green solid electrolyte body
According to this manufacturing method, a green insulating layer is formed, by means of screen printing, around a green solid electrolyte body formed on a support sheet. Therefore, it is possible to form a green plate-shaped member in which the green solid electrolyte body is surrounded by the green insulating layer without formation of a gap therebetween. Accordingly, it is possible to prevent deterioration of sensor performance, which deterioration would otherwise occur due to presence of a gap between the solid electrolyte body and the insulating layer.
The present invention can be implemented in various forms; for example, a gas sensor element, a gas sensor, a gas detection apparatus including the gas sensor, a vehicle having the gas detection apparatus mounted thereon, and methods of manufacturing the same.
Illustrative aspects of the invention will be described in detail with reference to the following figures wherein:
A. Overall Structure of Gas Sensor:
The gas sensor 100 extends along the axial line AX. The gas sensor 100 is fixedly attached to the outer surface of the exhaust pipe such that a forward portion (a lower portion on the paper on which
The gas sensor 100 includes a metallic shell 110 adapted to fixedly attach the same to the exhaust pipe. The metallic shell 110 is a tubular metal member which has a through-hole 110c extending therethrough along the axial line AX. The metallic shell 110 externally has a threaded portion 110a which is threadingly engaged with a threaded hole provided in the exhaust pipe for attachment of the gas sensor 100 to the exhaust pipe, and a tool engagement portion 110b with which a tool, such as a spanner or wrench, is engaged in attaching the gas sensor 100 to the exhaust pipe.
A closed-bottomed cylindrical protector 101 having a dual structure is laser-welded to a forward end portion of the metallic shell 110. The dual-structure protector 101 has a plurality of introduction holes 101c formed in inner and outer walls thereof for allowing introduction of exhaust gas into the gas sensor 100 attached to the exhaust pipe.
An outer tube 103 formed of metal is laser-welded to a rear end portion of the metallic shell 110. Three sensor lead wires 193, 194, and 195 and two heater lead wires 196 and 197 are inserted from a rear end portion of the outer tube 103 into the gas sensor 100 for electrical connection between the gas sensor 100 and an external control circuit (not shown). A grommet 191 formed of fluororubber is fitted into the rear end portion of the outer tube 103 for sealing the interior of the outer tube 103, and the five lead wires 193 to 197 are inserted into the outer tube 103 while extending through the grommet 191.
The gas sensor 100 includes a gas sensor element 120 which outputs a signal corresponding to oxygen concentration. The gas sensor element 120 has a laminate structure in which slender plate members are laminated together, and has a rectangular columnar shape having a substantially rectangular section taken perpendicularly to the imaginary center axis AX (details will be described later). The gas sensor element 120 is fixedly held in the through-hole 110c of the metallic shell 110 and is accommodated in the gas sensor 100 along the axial line AX. In
The gas sensor element 120 has a gas detecting section 121 formed at a forward end portion thereof (a lower end portion in
A separator 181 is a tubular insulating member which has a through-hole 181c extending along the axial line AX, and is fixedly held within the outer tube 103 attached to a rear end portion (an upper end portion in
Three sensor electrode pads 125, 126, and 127 are arrayed on the first surface 120a of the gas sensor element 120 at a rear end portion thereof in parallel toward the far side of the paper on which
The gas sensor element 120 is fixedly held in a tubular space of the metallic shell 110 through the following configurational features. The metallic shell 110 has a stepped portion 111 protruding radially inward into a forward end portion of the through-hole 110c thereof. A metal cup 116 having a through-hole 116c formed in the bottom thereof is disposed within the through-hole 110c of the metallic shell 110 in such a condition that an outer circumferential portion of the bottom thereof is engaged with the stepped portion 111.
A ceramic holder 113 is disposed within the metal cup 116 and on the bottom of the metal cup 116. The ceramic holder 113 is formed of alumina (Al2O3) and has a rectangular through-hole 113c formed at the center for allowing the gas sensor element 120 to extend therethrough.
A first powder filler layer 114 (talc) is formed within the metal cup 116 for airtightly holding the gas sensor element 120 which extends through the through-hole 116c of the metal cup 116 and through the through-hole 113c of the ceramic holder 113. The first powder filler layer 114 is formed by filling an internal space of the metal cup 116 above the ceramic holder 113 with talc powder. In this manner, the gas sensor element 120 is held in the through-hole 110c of the metallic shell 110 while being integrated with the metal cup 116, the ceramic holder 113, and the first powder filler layer 114.
Furthermore, a second powder filler layer 115 (talc) is formed, through charging of talc powder, on the first powder filler layer 114 in the through-hole 110c of the metallic shell 110 for securing airtightness between a rear end portion of the metallic shell 110 and the gas detecting section 121 of the gas sensor element 120. Additionally, a ceramic sleeve 170 is disposed on the second powder filler layer 115.
The ceramic sleeve 170 is a tubular member which has a rectangular axial hole 170c extending along the axial line AX for allowing the gas sensor element 120 to extend therethrough. The ceramic sleeve 170 can be formed of alumina. A rear end portion 110k of the metallic shell 110 is crimped radially inward, whereby the ceramic sleeve 170 is pressed toward the second powder filler layer 115 and fixed to the metallic shell 110. A crimp ring 117 is disposed between the ceramic sleeve 170 and the rear end portion 110k of the metallic shell 110.
As described with reference to
The protection layer 131 is a plate-shaped member formed primarily of alumina and protects the gas sensor element 120 from the first surface 120a side. The protection layer 131 has a porous section 132 formed at a forward end portion thereof and being gas-permeable in the direction of lamination thereof (in the vertical direction in
The three electrode pads 125 to 127 are arrayed in parallel in the width direction of the gas sensor element 120 (toward the far side of the paper on which
The oxygen pump cell 135 is a plate-shaped member which includes a solid electrolyte body 136, an insulating member 139 having the solid electrolyte body 136 disposed therein, and a pair of electrodes 137 and 138. The solid electrolyte body 136 is a plate-shaped member formed of, for example, stabilized zirconia sintered body or partially stabilized zirconia sintered body and having an area slightly greater than those of paired electrode portions 137M and 138M. In the present embodiment, the entire contour of the solid electrolyte body 136 forms a circular shape, or a portion of the counter corresponding to at least one side of the solid electrolyte body 136 (when it has one side or a plurality of sides) forms an arcuate shape. This point will be described in detail later. The insulating member 139 is a plate-shaped member which surrounds the outer perimeter of the solid electrolyte body 136 to cover the circumference of the solid electrolyte body 136 and which has a size substantially the same as that of the protection layer 131. The insulating member 139 has fourth and fifth through-hole conductors 14 and 15 formed therein at a rear end portion thereof in such a manner as to extend therethrough. The fourth and fifth through-hole conductors 14 and 15 electrically communicate with the second and third through-hole conductors 12 and 13, respectively, formed in the protection layer 131. The insulating member 139 is formed of, for example, alumina.
The two electrodes 137 and 138 are formed porously and primarily of platinum (Pt) and have the electrode portions 137M and 138M and lead portions 137L and 138L, respectively. The electrode portions 137M and 138M are disposed on a first surface 136a (an upper surface in
The lead portions 137L and 138L extend rearward from the electrode portions 137M and 138M, respectively. The lead portion 137L of the electrode 137 disposed on the first surface 136a electrically communicates with the first electrode pad 125 through the first through-hole conductor 11 provided in the protection layer 131. The lead portion 138L of the electrode 138 disposed on the second surface 136b electrically communicates with the second electrode pad 126 through the fourth through-hole conductor 14 provided in the insulating member 139 and through the second through-hole conductor 12 provided in the protection layer 131.
The spacer 145 is a plate-shaped insulating member having a size substantially the same as that of the insulating member 139 of the oxygen pump cell 135. The spacer 145 is formed of, for example, alumina. The spacer 145 has a through-hole formed at a forward end portion thereof. The through-hole partially constitutes the gas detecting chamber 145c, into which exhaust gas to be measured is introduced, when the spacer 145 is sandwiched between the oxygen pump cell 135 and the oxygen concentration detection cell 150.
The spacer 145 has diffusion controlling portions 146 formed at two respective side wall portions which face each other in the width direction of the spacer 145 with the through-hole intervening therebetween. The diffusion controlling portions 146 are formed of gas-permeable porous alumina. In the gas sensor element 120, exhaust gas is introduced into the gas detecting chamber 145c in an amount corresponding to gas permeability of the diffusion controlling portions 146. That is, the diffusion controlling portions 146 function as gas introducing portions of the gas detecting section 121.
The spacer 145 has a sixth through-hole conductor 16 formed therein at a rear end portion thereof in such a manner as to extend therethrough. The sixth through-hole conductor 16 electrically communicates with the lead portion 138L of the electrode 138 of the oxygen pump cell 135. The spacer 145 also has a seventh through-hole conductor 17 formed therein adjacent to the sixth through-hole conductor 16 in such a manner as to extend therethrough. The seventh through-hole conductor 17 electrically communicates with the fifth through-hole conductor 15 provided in the insulating member 139 of the oxygen pump cell 135.
The spacer 145 functions as an insulating layer for electrically insulating the oxygen pump cell 135 and the oxygen concentration detection cell 150 from each other.
The oxygen concentration detection cell 150 is a plate-shaped member which includes a solid electrolyte body 151, an insulating member 154 having the solid electrolyte body 151 disposed therein, and a pair of electrodes 152 and 153. The solid electrolyte body 151 is a plate-shaped member formed of, for example, stabilized zirconia sintered body or partially stabilized zirconia sintered body and having an area slightly greater than those of paired electrode portions 152M and 153M. Like the solid electrolyte body 136 of the oxygen pump cell 135, the entire contour of the solid electrolyte body 151 forms a circular shape, or a portion of the counter corresponding to at least one side of the solid electrolyte body 151 (when it has one side or a plurality of sides) forms an arcuate shape. The insulating member 154 is a plate-shaped member which surrounds the outer perimeter of the solid electrolyte body 151 to cover the circumference of the solid electrolyte body 151 and which has a size substantially the same as that of the spacer 145. The insulating member 154 has an eighth through-hole conductor 18 formed therein at a rear end portion thereof in such a manner as to extend therethrough. The eighth through-hole conductor 18 electrically communicates with the seventh through-hole conductor 17 formed in the spacer 145.
The two electrodes 152 and 153 are formed porously and primarily of platinum (Pt) and have the electrode portions 152M and 153M and lead portions 152L and 153L, respectively. The electrode portions 152M and 153M are disposed on a first surface 151a (an upper surface in
The lead portion 152L of the electrode 152 disposed on the first surface 151a electrically communicates with the electrode 138 of the oxygen pump cell 135 and with the second electrode pad 126 through the sixth through-hole conductor 16 provided in the spacer 145. The lead portion 153L of the electrode 153 disposed on the second surface 150b electrically communicates with the third electrode pad 127 through the eighth through-hole conductor 18 provided in the insulating member 154.
The heater element 160 includes first and second insulators 161 and 162, a heat-generating resistor 163, and first and second heater lead portions 164 and 165. Each of the first and second insulators 161 and 162 is a plate-shaped member formed of alumina and having the same size as the detection element 130. The first and second insulators 161 and 162 holds the heat-generating resistor 163 and the heater lead portions 164 and 165 therebetween.
The heat-generating resistor 163 is a heat-generating wire formed primarily of platinum and having a meandering shape. The two heater lead portions 164 and 165 are connected to respective opposite ends of the heat-generating resistor 163 and extend rearward from the respective opposite ends of the heat-generating resistor 163.
The second insulator 162 has first and second heater electrode pads 128 and 129 arrayed in parallel in the width direction of the heater element 160 on an outer surface 162b of the second insulator 162 at a rear end portion thereof. Also, the second insulator 162 has first and second heater through-hole conductors 21 and 22 formed therein in such a manner as to extend therethrough. The first and second heater through-hole conductors 21 and 22 correspond to the first and second heater electrode pads 128 and 129. The first and second heater lead portions 164 and 165 extending from the heat-generating resistor 163 electrically communicate with the first and second heater electrode pads 128 and 129 through the first and second heater through-hole conductors 21 and 22, respectively.
When the gas sensor 100 is driven, the heater element 160 is controlled in heat temperature by an external heater control circuit (not shown). The heater element 160 heats the detecting element 130 to a temperature of several hundred ° C. (e.g., 700° C. to 800° C.) for activating the oxygen pump cell 135 and the oxygen concentration detection cell 150.
B. Shape of Solid Electrolyte Body and Method of Manufacturing the Same:
The solid electrolyte body 136 of
Each of the solid electrolyte bodies 136 shown in
In a step shown in
As described above, in the present embodiment, the solid electrolyte body 136 embedded in the through-hole of the insulating member 139 does not have a rectangular contour but has a contour which forms an arcuate shape projecting toward at least one side of the four sides of the insulating member 139. Therefore, the solid electrolyte body 136 having such a contour has an advantage that, even when an external force or a stress such as thermal stress acts on the solid electrolyte body 136, stress concentration is less likely to occur. Also, when the green insulating layer 139p is formed around the green solid electrolyte body 136p by means of printing, air is less likely to remain between the green solid electrolyte body 136p and the green insulating layer 139p. Therefore, the possibility of formation of a useless gap between the green solid electrolyte body 136p and the green insulating layer 139p can be decreased.
C. Modifications:
The present invention is not limited to the above-described embodiment, but may be embodied in various other forms without departing from the gist of the invention.
The overall structure of the above-described gas sensor 100 is a mere example, and various other structures may be employed. Also, in the above-described embodiments, the gas sensor 100 detects the concentration of oxygen gas contained in gas to be measured, by using the oxygen-ion conductive solid electrolyte bodies 136 and 151. However, the present invention can be applied to a gas sensor which detects the concentration of a gas other than oxygen.
Number | Date | Country | Kind |
---|---|---|---|
2014-011385 | Jan 2014 | JP | national |
2014-212197 | Oct 2014 | JP | national |