JP5965734B2 - Sensor element - Google Patents

Description

  The present invention relates to a sensor element.

  Conventionally, gas sensors for detecting specific gas components such as nitrogen oxide (NOx) and oxygen and measuring the concentration of specific gas components are known (for example, Patent Documents 1 and 2). The gas sensor includes a sensor element that outputs a detection signal such as a concentration.

  The sensor element includes a solid electrolyte layer, an electrode part, and a lead part. The solid electrolyte layer is a plate-like member that is formed mainly of zirconia, for example, and extends in the longitudinal direction. The electrode part is formed of, for example, platinum as a main component and is laminated on the solid electrolyte layer. The lead portion is formed of, for example, platinum as a main component, is laminated on the solid electrolyte layer, and is electrically connected to the electrode portion. The lead portion extends in the longitudinal direction and is narrower than the electrode portion.

JP 2010-66192 A JP 2010-122187 A

  The electrode part and the lead part are formed on the solid electrolyte layer by printing and drying a paste containing a conductive material such as platinum on the solid electrolyte layer. Here, when the electrode part and the lead part are formed on the solid electrolyte layer, a crack may occur in the connection part that is a boundary between the lead part and the electrode part.

  In order to reduce the occurrence of cracks at the connection part, it is conceivable to change the composition of the paste for forming the electrode part and the lead part. However, a change in the composition of the paste may cause problems such as a decrease in detection accuracy.

  Therefore, an object of this invention is to provide the technique which can reduce generation | occurrence | production of the crack in a connection part by devising the shape of a connection part.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
[Form 1]
A plate-like solid electrolyte layer extending in the longitudinal direction, a pair of electrode parts laminated on the solid electrolyte layer, laminated on the solid electrolyte layer, and electrically connected to the electrode part in the longitudinal direction In a sensor element comprising a pair of lead portions that extend and narrower than the electrode portion,
It is located between the electrode part and the lead part, and has a connection part for connecting the electrode part and the lead part,
The width of the lead portion is less than 50% of the width of the electrode portion,
Both side surfaces of the connection part are round surfaces that are convex inward with a radius of 0.4 mm or more when the sensor element is viewed along the stacking direction.
Of the longitudinal direction, when the electrode portion is disposed on the tip side, and the lead portion is disposed on the rear end side,
The sensor element according to claim 1, wherein an outer side surface provided on a front end side in the longitudinal direction among both side surfaces of the connection portion is positioned on a front end side with respect to a rear end of the electrode portion.
According to this embodiment, when the electrode part and the lead part are arranged on both sides of the solid electrolyte layer by making the width of the lead part narrower than the width of the electrode part, a pair of leads arranged on both sides The distance between the parts can be increased. Thereby, insulation of a pair of lead part can be aimed at satisfactorily. In addition, in the sensor element in which the width of the lead portion is less than 50% of the width of the electrode portion, the shape of the both side surfaces of the connection portion is a rounded surface that protrudes inward with a radius of 0.4 mm or more, so that the electrode portion Even if the width of the lead portion is narrower than the width of the lead, the occurrence of cracks at the connecting portion can be reduced. Further, it is possible to reduce the possibility of occurrence of a portion where the width of the connection portion becomes extremely short in the short direction. Thereby, possibility that the electrical connection of an electrode part and a lead part will be interrupted | blocked can be reduced.

[Application Example 1] A plate-like solid electrolyte layer extending in the longitudinal direction, a pair of electrode parts laminated on the solid electrolyte layer, and laminated on the solid electrolyte layer and electrically connected to the electrode part. In the sensor element comprising a pair of lead portions extending in the longitudinal direction and having a width narrower than the electrode portion,
It is located between the electrode part and the lead part, and has a connection part for connecting the electrode part and the lead part,
The width of the lead portion is less than 50% of the width of the electrode portion,
Both side surfaces of the connecting portion are rounded surfaces that are convex inward with a radius of 0.4 mm or more when the sensor element is viewed in the stacking direction.
According to the sensor element described in Application Example 1, when the electrode part and the lead part are arranged on both sides of the solid electrolyte layer by making the width of the lead part narrower than the width of the electrode part, The distance between the pair of lead portions arranged can be increased. Thereby, insulation of a pair of lead part can be aimed at satisfactorily.
In addition, in the sensor element in which the width of the lead portion is less than 50% of the width of the electrode portion, the shape of the both side surfaces of the connection portion is a rounded surface that protrudes inward with a radius of 0.4 mm or more, so that the electrode portion Even if the width of the lead portion is narrower than the width of the lead, the occurrence of cracks at the connecting portion can be reduced.

[Application Example 2] In the sensor element according to Application Example 1,
The sensor element, wherein the electrode part and the lead part are arranged in different ranges in the lateral direction of the solid electrolyte layer perpendicular to the longitudinal direction.
According to the sensor element described in Application Example 2, when the electrode part and the lead part are arranged on both sides of the solid electrolyte layer, the distance between the pair of lead parts arranged on both sides can be made longer. Thereby, insulation of a pair of lead part can be aimed at more favorably.

[Application Example 3] In the sensor element according to Application Example 1 or Application Example 2,
Of the longitudinal direction, when the electrode portion is disposed on the tip side, and the lead portion is disposed on the rear end side,
The sensor element according to claim 1, wherein an outer side surface provided on a front end side in the longitudinal direction among both side surfaces of the connection portion is positioned on a front end side with respect to a rear end of the electrode portion.
According to the sensor element described in the application example 3, it is possible to reduce the possibility of occurrence of a portion in which the width of the connection portion becomes extremely short in the short direction. Thereby, possibility that the electrical connection of an electrode part and a lead part will be interrupted | blocked can be reduced.

  In addition, this invention can be implement | achieved with various forms, for example, can be implement | achieved in aspects, such as a manufacturing method of a sensor element, a gas sensor provided with the sensor element, an internal combustion engine provided with the gas sensor.

It is sectional drawing which shows the gas sensor 200 as an Example of this invention. 1 is a cross-sectional view of a sensor element 10. FIG. 1 is an exploded perspective view of a sensor element 10. FIG. It is a figure for demonstrating the detail of an electrode unit. It is a graph which shows a 1st experiment result. It is a graph which shows a 2nd experiment result. It is a figure for demonstrating the electrode unit 300a of a 1st modification.

Next, embodiments of the present invention will be described in the following order.
A. Example:
B. Variations:

A. Example:
A-1: Overall configuration of the gas sensor:
FIG. 1 is a cross-sectional view showing a gas sensor 200 as an embodiment of the present invention. This gas sensor 200 is fixed to an exhaust pipe of an internal combustion engine (engine) (not shown) and measures the concentration of nitrogen oxides (NOx) (hereinafter, the gas sensor 200 is also referred to as “NOx sensor 200”). FIG. 1 shows a cross section of the NOx sensor 200 parallel to the longitudinal direction D1. Hereinafter, the downward direction (lower side) in FIG. 1 is referred to as the front end side FWD of the NOx sensor 200, and the upward direction (upper side) in FIG. 1 is referred to as the rear end side BWD of the NOx sensor 200.

  The NOx sensor 200 includes a cylindrical metal shell 138, a sensor element 10 having a plate shape extending in the longitudinal direction D1 (also simply referred to as “sensor element 10”), and a cylindrical ceramic sleeve 106 surrounding the sensor element 10. Insulating contact member 166 and six connection terminals 110 (four are shown in FIG. 1). A threaded portion 139 for fixing to the exhaust pipe is formed on the outer surface of the metal shell 138. The ceramic sleeve 106 is disposed so as to surround the periphery of the sensor element 10 in the radial direction. The insulating contact member 166 is formed with a contact insertion hole 168 penetrating in the longitudinal direction D1. The insulating contact member 166 is arranged so that the inner wall surface of the contact insertion hole 168 surrounds the periphery of the rear end portion of the sensor element 10. Each connection terminal 110 is disposed between the sensor element 10 and the insulating contact member 166.

  The metal shell 138 has a substantially cylindrical shape having a through hole 154 that penetrates in the axial direction (also referred to as “longitudinal direction D1”) and a shelf 152 that projects radially inward of the through hole 154. Yes. The metal shell 138 has a sensor element 10 such that the front end of the sensor element 10 is disposed outside the front end side FWD of the through hole 154 and the rear end side of the sensor element 10 is disposed outside the rear end side BWD of the through hole 154. 10 is held in the through hole 154. The shelf 152 includes a tapered surface inclined with respect to a plane perpendicular to the longitudinal direction D1. The tapered surface is formed so that the diameter of the front end side FWD is smaller than the diameter of the rear end side BWD.

  Inside the through hole 154 of the metal shell 138, a ceramic holder 151, powder filling layers 153 and 156 (hereinafter also referred to as talc rings 153 and 156), and a ceramic sleeve 106 are arranged in this order from the front end side FWD to the rear end side BWD. It is laminated. The sensor element 10 is held by the ceramic holder 151, the talc rings 153 and 156, and the ceramic sleeve 106.

  A caulking packing 157 is disposed between the ceramic sleeve 106 and the rear end portion 140 of the metal shell 138. Between the ceramic holder 151 and the shelf 152 of the metal shell 138, a talc ring 153 and a metal holder 158 for holding the ceramic holder 151 are disposed. Note that the rear end portion 140 of the metal shell 138 is crimped so as to press the ceramic sleeve 106 toward the distal end side via the crimping packing 157.

  In addition, an external protector 142 and an internal protector 143 are attached to the outer periphery of the front end side FWD of the metal shell 138 by welding or the like. The double protectors 142 and 143 are formed of a metal having a plurality of holes (for example, stainless steel) and cover the protruding portion of the sensor element 10.

  An outer cylinder 144 is fixed to the outer periphery of the rear end side BWD of the metal shell 138. A grommet 150 is disposed in the opening of the rear end side BWD of the outer cylinder 144. A lead wire insertion hole 161 is formed in the grommet 150. Six lead wires 146 are inserted through the lead wire insertion holes 161 (only five lead wires 146 are shown in FIG. 1). These lead wires 146 are electrically connected to electrode pads (not shown) provided on the outer surface of the rear end side BWD of the sensor element 10, respectively.

  An insulating contact member 166 is disposed on the rear end side BWD of the sensor element 10 protruding from the rear end portion 140 of the metal shell 138. The insulating contact member 166 is disposed around an electrode pad (not shown) formed on the surface of the rear end side BWD of the sensor element 10. The insulating contact member 166 is formed in a cylindrical shape and has a contact insertion hole 168 penetrating in the longitudinal direction D1. The insulating contact member 166 has a flange 167 that protrudes radially outward from the outer surface. A holding member 169 is inserted between the insulating contact member 166 and the outer cylinder 144. The holding member 169 arranges the insulating contact member 166 inside the outer cylinder 144 by contacting the outer cylinder 144 and the flange portion 167.

  FIG. 2 is a cross-sectional view of the sensor element 10. In FIG. 2, the tip side portion of the sensor element 10 is shown. This sectional view shows a section parallel to the longitudinal direction D1. In FIG. 2, the left direction indicates the front end direction (front end side) FWD, and the right direction indicates the rear end direction (rear end side) BWD. The sensor element 10 has a structure in which an insulating layer 14e, a first solid electrolyte layer 11a, an insulating layer 14a, a second solid electrolyte layer 12a, an insulating layer 14b, a third solid electrolyte layer 13a, and insulating layers 14c and 14d are stacked in this order. Have These layers are stacked along a stacking direction D2 perpendicular to the longitudinal direction D1. In the drawing, the insulating layer 14e is shown separated from the first solid electrolyte layer 11a for ease of explanation, but actually, the insulating layer 14e is laminated on the first solid electrolyte layer 11a. Has been.

  A first measurement chamber 16 is formed between the first solid electrolyte layer 11a and the second solid electrolyte layer 12a. A measurement gas GM is introduced from the outside through a first diffusion resistor 15a disposed at the left end (inlet) of the first measurement chamber 16. A second diffusion resistor 15b is disposed at the end of the first measurement chamber 16 opposite to the inlet.

  On the right side of the first measurement chamber 16, a second measurement chamber 18 communicating with the first measurement chamber 16 through the second diffusion resistor 15b is formed. The second measurement chamber 18 penetrates the second solid electrolyte layer 12a and is formed between the first solid electrolyte layer 11a and the third solid electrolyte layer 13a.

  A heater 50 extending along the longitudinal direction D1 is embedded between the insulating layers 14c and 14d. The heater 50 is used to stabilize the operation by raising the temperature of the gas sensor element 10 to a predetermined activation temperature and increasing the conductivity of oxygen ions in the solid electrolyte layer. The heater 50 is a heating resistor formed of a conductor such as tungsten, and generates heat by supplied power. The heater 50 is supported by the two layers 14c and 14d.

  In the present embodiment, the solid electrolyte layers 11a, 12a, and 13a are each formed using zirconia having oxygen ion conductivity as a main component. The insulating layers 14a to 14e are formed using alumina as a main component, and the first diffusion resistor 15a and the second diffusion resistor 15b are formed using a porous material such as alumina. The main component indicates that “the content of the main material in the ceramic layer is 50 wt% or more, for example, the solid electrolyte layer contains 50 wt% or more of zirconia”. Six layers 14e, 11a, 12a, 13a, 14c, and 14d of the eight layers of the solid electrolyte layer and the insulating layer are each formed using a raw material sheet (for example, zirconia or alumina). Ceramic sheet). The two insulating layers 14a and 14b are formed by screen printing on a ceramic sheet. And the sensor element 10 is formed by baking the laminated body obtained by laminating | stacking each layer before baking.

  The gas sensor element 10 includes a first pumping cell 11, an oxygen concentration detection cell 12, and a second pumping cell 13.

  The first pumping cell 11 includes a first solid electrolyte layer 11a, an inner first electrode unit 11c arranged so as to sandwich the first solid electrolyte layer 11a, and an outer first electrode unit 11b which is a counter electrode. The inner first electrode unit 11 c faces the first measurement chamber 16. Both the inner first electrode unit 11c and the outer first electrode unit 11b are formed mainly of platinum. The surface of the inner first electrode unit 11c is covered with a protective layer 11e made of a porous body. Further, the outer first electrode unit 11b is made of a porous 11d (for example, alumina) through which a gas (for example, oxygen) can be passed, which is embedded in a portion of the insulating layer 14e facing the outer first electrode unit 11b. Covered.

  The oxygen concentration detection cell 12 includes a second solid electrolyte layer 12a, and a detection electrode unit 12b and a reference electrode unit 12c arranged so as to sandwich the second solid electrolyte layer 12a. Each of the detection electrode unit 12b and the reference electrode unit 12c is formed mainly of platinum.

  The insulating layer 14b is cut out so that the reference electrode unit 12c in contact with the second solid electrolyte layer 12a is disposed inside. The cutout portion is filled with a porous body to form a reference oxygen chamber 17. Oxygen is sent from the first measurement chamber 16 into the reference oxygen chamber 17 by passing a weak constant current through the oxygen concentration detection cell 12 in advance. The oxygen concentration in the reference oxygen chamber 17 is maintained at a predetermined concentration. Thereby, the reference oxygen chamber 17 is used as a reference for the oxygen concentration.

  The second pumping cell 13 includes a third solid electrolyte layer 13a, an inner second pump electrode unit 13b disposed on the surface of the third solid electrolyte layer 13a facing the second measurement chamber 18, and a counter electrode. 2 counter electrode unit (counter electrode 2nd pump electrode unit) 13c. The inner second pump electrode unit 13b and the counter second pump electrode unit 13c are both formed mainly of platinum. The electrode part of the counter electrode second pump electrode unit 13c is disposed in the cutout part of the insulating layer 14b on the third solid electrolyte layer 13a and faces the reference oxygen chamber 17 so as to face the electrode part of the reference electrode unit 12c. ing.

  2 also shows the control unit CU of the NOx sensor 200 (sensor element 10). The heater 50 and the electrode units 11b, 11c, 12b, 12c, 13b, and 13c are connected to the control unit CU via the connection terminals 110 and the lead wires 146 shown in FIG. As will be described later, the control unit CU supplies power to the heater 50. Further, the control unit CU controls the NOx sensor 200 (sensor element 10) by transmitting and receiving signals to and from the electrode units 11b, 11c, 12b, 12c, 13b, and 13c. In the present embodiment, the control unit CU is an electronic circuit formed using an operational amplifier or the like. The control unit CU may be formed using a computer having a CPU and a memory.

  Next, an example of the operation of the sensor element 10 will be described. First, the control unit CU is activated by starting the engine. The control unit CU supplies power to the heater 50. The heater 50 heats the first pumping cell 11, the oxygen concentration detection cell 12, and the second pumping cell 13 to the activation temperature. Then, the control unit CU causes a current to flow through the first pumping cell 11 in response to each cell 11 to 13 being heated to the activation temperature. As a result, the first pumping cell 11 pumps excess oxygen in the gas to be measured (exhaust gas) GM flowing into the first measurement chamber 16 from the inner first electrode unit 11c toward the outer first electrode unit 11b.

  The control unit CU controls the interelectrode voltage (inter-terminal voltage) of the first pumping cell 11 so that the inter-electrode voltage (inter-terminal voltage) of the oxygen concentration detection cell 12 becomes a constant voltage V1 (for example, 425 mV). The voltage of the oxygen concentration detection cell 12 represents the oxygen concentration in the detection electrode unit 12b. By this control, the oxygen concentration in the first measurement chamber 16 is adjusted to the extent that NOx is not decomposed.

  The gas to be measured GN whose oxygen concentration is adjusted further flows toward the second measurement chamber 18. The control unit CU applies an interelectrode voltage (interterminal voltage) to the second pumping cell 13. This voltage is set to a constant voltage such that the NOx gas in the measurement gas GN is decomposed into oxygen and nitrogen gas (a voltage higher than the control voltage value of the oxygen concentration detection cell 12, for example, 450 mV). Thereby, NOx in the measurement gas GN is decomposed into nitrogen and oxygen.

  The control unit CU supplies a second pump current to the second pumping cell 13 so as to pump out oxygen generated by the decomposition of NOx from the second measurement chamber 18. Since there is a linear relationship between the second pump current and the NOx concentration, the NOx concentration in the measurement gas GN can be detected by detecting the current.

  FIG. 3 is an exploded perspective view of the sensor element 10. Three electrode pads 125, 126, and 127 are formed on the outer surface of the insulating layer 14e. Three electrode pads 128, 129, and 130 are formed on the outer surface of the insulating layer 14d.

  Three through holes H15, H16, and H17 are formed in the insulating layer 14e. Two through holes H26 and H27 are formed in the first solid electrolyte layer 11a. In the insulating layer 14 a, two through holes H 36 and H 37, a through hole 18 a constituting a part of the second measurement chamber 18, and the first measurement chamber 16 are formed. In the second solid electrolyte layer 12a, two through holes H46 and H47 and a through hole 18b constituting a part of the second measurement chamber 18 are formed. In the insulating layer 14 b, one through hole H 57, a through hole 18 c constituting a part of the second measurement chamber 18, and a reference oxygen chamber 17 are formed. One through hole H66 is formed in the third solid electrolyte layer 13a. One through hole H76 is formed in the insulating layer 14c. In addition, a connection line L76 for electrically connecting the two through holes H66 and H76 is formed in the insulating layer 14c. Three through holes H86, H88, and H89 are formed in the insulating layer 14d. Each through hole is formed by making a hole in a ceramic sheet before firing. In addition, the through-hole conductor is formed in the through hole after firing by forming a conductive paste before firing.

  The outer first electrode unit 11b is disposed on one of the two main surfaces of the first solid electrolyte layer 11a. The inner first electrode unit 11c is disposed on the other surface of the two main surfaces of the first solid electrolyte layer 11a. The electrode portions of the outer first electrode unit 11b and the inner first electrode unit 11c are opposed to each other with the first solid electrolyte layer 11a interposed therebetween.

  The detection electrode unit 12b is disposed on one of the two main surfaces of the second solid electrolyte layer 12a. The reference electrode unit 12c is disposed on the other surface of the two main surfaces of the second solid electrolyte layer 12a. Specifically, the electrode portions of the detection electrode unit 12b and the reference electrode unit 12c face each other with the second solid electrolyte layer 12a interposed therebetween.

  The counter second pump electrode unit 13c and the inner second pump electrode unit 13b are disposed on one of the two main surfaces of the third solid electrolyte layer 13a. The electrode portions of the counter electrode second pump electrode 13c and the reference electrode unit 12c face each other with the reference oxygen chamber 17 interposed therebetween.

  The inner first electrode unit 11c, the detection electrode unit 12b, and the inner second pump electrode unit 13b are electrically connected to the electrode pad 124 through through holes H17, H27, H37, H47, and H57. The electrode pad 127 is connected to a reference potential. The outer first electrode unit 11b is electrically connected to the electrode pad 125 through the through hole H15. The reference electrode unit 12c is electrically connected to the electrode pad 126 through the through holes H16, H26, H36, and H46. The counter electrode second pump electrode unit 13c is electrically connected to the electrode pad 130 through the through holes H86, H76, H66 and the connection line L76. In the heater 50, one lead wire is electrically connected to the electrode pad 128 via the through hole H88, and the other lead wire is electrically connected to the electrode pad 129 via the through hole H89.

A-2. Detailed configuration of electrode unit:
FIG. 4 is a diagram for explaining the details of the electrode unit. FIG. 4 is a view of the front end portion of the outer first electrode unit 11b when viewed along the stacking direction D2. Here, the outer first electrode unit 11b will be described, but the other electrode units (for example, the inner first electrode unit 11c) have the same configuration. Hereinafter, the electrode units 11b, 11c, 12b, 12c, 13c, and 13b are also referred to as “electrode units 300” when used without distinction.

  The electrode unit 300 includes an electrode part 302, a connection part 303, and a lead part 304 in order from the front end side FWD to the rear end side BWD. In addition, the dotted line is attached | subjected to the boundary of each part 302,303,304. The electrode section 302 is used for NOx concentration detection performed by the gas sensor element 10 when a current flows between the electrode section 302 and the counter electrode section 302.

  The lead unit 304 is used to electrically connect the electrode unit 302 and the outside (specifically, the control unit CU). The lead portion 304 extends in the longitudinal direction D1, and is electrically connected to the corresponding electrode pads 125, 126, 127, 130 at the rear end portion located on the rear end side BWD. The width B of the lead part 304 is narrower than the width A of the electrode part 302. Thereby, when the electrode part 302 and the lead part 304 are arrange | positioned on both sides on both sides of solid electrolyte layer 11a, 12a, the distance of a pair of lead part 304 arrange | positioned on both sides can be lengthened. Thereby, insulation of a pair of lead part 304 can be aimed at satisfactorily.

  The connection part 303 is located between the electrode part 302 and the lead part 304, and electrically connects the electrode part 302 and the lead part 304. That is, it can be said that the connection portion 303 is a boundary portion between the electrode portion 302 and the lead portion 304. On both side surfaces of the connecting portion 303, convex round surfaces 310 and 312 are formed inwardly. For convenience of explanation, one of the rounded surfaces 310 and 312 is also referred to as a “first rounded surface 310”, and the other is also referred to as a “second rounded surface 312”. The first radius surface 310 has a radius Ra. The second rounded surface 312 has a radius Rb. The first radius surface 310 has a radius center Pa located on the rear end side BWD from the electrode portion 302. In the second rounded surface 312, the rounded center Pb is located on the front end side FWD from the lead portion 304. In the present embodiment, the second rounded surface 312 is provided on the front end side FWD with respect to the first rounded surface 310. Here, the second rounded surface 312 corresponds to the “outer surface” described in the means for solving the problem.

  In the electrode unit 300 as described above, for example, a paste containing platinum as a main component is printed on the corresponding solid electrolyte layers 11a, 12a, and 13a with a screen mask, and at a predetermined temperature (for example, 80 to 90 ° C.) after printing. It can be formed by drying.

  Here, it is preferable that the electrode part 302 and the lead part 304 are arranged in different ranges in the lateral direction D3 orthogonal to the longitudinal direction D1. That is, as illustrated in FIG. 4, it is preferable that the range Da in which the electrode portion 302 is located and the range Db in which the lead portion 304 is located are shifted without overlapping in the short direction D3. In this way, when the electrode units 11b, 11c, 12b, and 12c are disposed with the solid electrolyte layers 11a and 12a interposed therebetween, the distance between the pair of lead portions 304 disposed on both sides can be increased. That is, an electrode unit (also simply referred to as a “counter electrode unit”) that serves as a counter electrode of the electrode unit 300 shown in FIG. 4 is inverted about the longitudinal direction D1 to connect the electrode unit 300 and the counter electrode unit to the solid electrolyte layer 11a, It arrange | positions on both sides of 12a. Thereby, the possibility that the lead part 304 of the electrode unit 300 and the lead part of the counter electrode unit face each other with the solid electrolyte layers 11a and 12a interposed therebetween can be further reduced. Thereby, insulation of a pair of lead part 304 can be aimed at better.

  Further, the second rounded surface 312 is preferably located on the front end side FWD from the rear end 330 of the electrode portion 302. In the electrode unit 300 shown in FIG. 4, the second rounded surface 312 is located on the front end side FWD by a distance La from the rear end 330. In other words, it is preferable that the first rounded surface 310 and the second rounded surface 312 are located in different ranges in the longitudinal direction D1. By doing so, the possibility that the width of the connection portion 303 (the length in the short direction D3) becomes extremely short can be reduced. Thereby, the possibility that the electrical connection between the electrode portion 302 and the lead portion 304 is interrupted can be reduced.

A-3. Experimental result:
The evaluation test was performed according to the following procedure. That is, a paste containing platinum as a main component is printed on a green sheet with a screen mask to form the electrode unit 300 before drying. Next, the green sheet on which the paste is printed is placed in the dryer. Then, it is dried for 3 minutes at a drying temperature of 95 ° C. in a dryer, and then the green sheet is taken out and left in the atmosphere for 5 minutes. This cycle is repeated five times, and then it is determined whether or not a crack has occurred in the electrode unit 300 by viewing with a magnifier. The ratio of the electrode units 300 in which cracks occurred to the plurality of produced electrode units 300 was defined as the occurrence rate VD (%). In the dried electrode unit 300, the electrode portion 302 had a thickness of 15 μm, and the lead portion 304 had a thickness of 25 μm. Further, the thickness of the connection part 303 after drying was set to a value between the thicknesses of the electrode part 302 and the lead part 304, and the thickness was increased as the electrode part 302 was closer to the lead part 304. In addition, the paste composition used for preparation of the electrode unit 300 is as follows.

<Paste composition> Ratio to platinum 100 (wt%)
Platinum 100
Ceramic powder 20
Organic binder 8
Solvent 25

A-3-1. First experiment results:
With respect to the shape of the electrode unit 300, the evaluation test was performed using a sample in which the ratio (B / A) of the width A of the electrode portion 302 and the width B of the lead portion was changed. The ratio of the width A and the width B (width ratio) was changed by fixing the width B to 0.39 mm and changing the width A. 100 samples were prepared for each sample. Note that the radii Ra and Rb of the connection portion 303 of each sample used in the first experiment are both 0.3 mm.

  FIG. 5 is a graph showing the results of the first experiment. The horizontal axis indicates the width ratio (B / A), and the vertical axis indicates the occurrence rate VD.

A-3-2. Results of the second experiment:
With respect to the shape of the electrode unit 300, the evaluation test was performed using a sample in which the width ratio (B / A) was constant (13%) and the radii Ra and Rb were both changed. The width A of the sample used in the second experiment is 3.1 mm, and the width B is 0.39 mm. That is, the sample No. described in FIG. Samples having the same values as 1 and widths A and B were used. In addition, 100 each sample was produced.

  FIG. 6 is a graph showing the results of the second experiment. The horizontal axis indicates the values of the radii Ra and Rb, and the vertical axis indicates the occurrence rate VD.

A-4. effect:
As shown in FIG. 5, the incidence rate VD was 0% in the samples with the radii Ra and Rb of 0.3 mm and the width ratio B / A of 50% or more, whereas the radii Ra and Rb were 0.3 mm. Sample No. having a width ratio B / A of 40%. In No. 1, the incidence VD was 0.4%. Furthermore, the incidence VD increased in the samples where the radii Ra and Rb were 0.3 mm and the width ratio B / A was less than 50%. That is, it can be seen that a crack occurs in the connection portion 303 when the width of the lead portion is less than 50% of the width of the electrode portion in order to achieve good insulation between the pair of lead portions.
However, as shown in FIG. In the evaluation test in which the radii Ra and Rb were changed in the same sample as 1, the incidence VD was 0% when the radii Ra and Rb were 0.4 mm or more. That is, as shown in FIG. 5, the side surfaces 310 and 312 of the connection portion 303 in which the incidence VD increases (that is, cracks occur in the connection portion 303) are rounded convex surfaces, and the radius of the rounded surface is By setting the thickness to 0.4 mm or more, generation of cracks at the connection portion 303 could be reduced. In addition, since the occurrence of cracks is reduced by the shape of both side surfaces 310 and 312 of the connection portion 303, the degree of freedom in designing the paste composition for forming the electrode unit 300 can be improved.

B. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various forms without departing from the gist thereof. For example, the following modifications are possible.

B-1. First modification:
FIG. 7 is a view for explaining an electrode unit 300a of a first modification. The difference from the electrode unit 300 of the first embodiment is the shape of the connecting portion 303a. Since the other configuration is the same as that of the first embodiment, the same reference numeral is given to the same configuration and the description thereof is omitted. In addition, the dotted line is attached | subjected to the boundary of the electrode part 302, the connection part 303a, and the lead part 304. FIG. In the first embodiment, the connection portion 303 has a relationship in which the range Da where the electrode portion 302 is located and the range Db where the lead portion 304 is located are shifted without overlapping in the short direction D3. However, when both side surfaces 310a and 312a of the connection portion 303a are viewed along the stacking direction of the sensor element 10, the both side surfaces 310a and 312a of the connection portion 303a are convex inward surfaces having a radius of 0.4 mm or more. As long as this is true, the relationship may be such that all of the range Db is located within the range Da as in the electrode unit 300a of the first modification. Even in this case, since the radii Rc and Rd of the both side surfaces 310a and 312a which are round surfaces are 0.4 mm or more, the occurrence of cracks in the connecting portion 303a can be reduced as in the first embodiment.

DESCRIPTION OF SYMBOLS 10 ... Sensor element 11 ... 1st pumping cell 11a ... 1st solid electrolyte layer 11b ... Outer side 1st electrode unit 11c ... Inner 1st electrode unit 11d ... Porous 11e ... Protective layer 12 ... Oxygen concentration detection cell 12a ... 2nd solid Electrolyte layer 12b ... detection electrode unit 12c ... reference electrode unit 13 ... second pumping cell 13a ... third solid electrolyte layer 13b ... inner second pump electrode unit 13c ... counter electrode second pump electrode unit 14a, 14b, 14c, 14d, 14e ... Insulating layer 15a ... First diffusion resistor 15b ... Second diffusion resistor 16 ... First measurement chamber 17 ... Reference oxygen chamber 18 ... Second measurement chamber 18a, 18b, 18c ... Through hole 50 ... Heater 110 ... Connection terminal 138 Metal shell 200 Gas sensor 300 Electrode unit 300a Electrode unit 302 Electrode unit 3 3 ... connection portion 303a ... connecting portion 304 ... lead portions 310, 312 ... side 310a, 312a ... side surface 330 ... rear

Claims (2)

A plate-like solid electrolyte layer extending in the longitudinal direction, a pair of electrode parts laminated on the solid electrolyte layer, laminated on the solid electrolyte layer, and electrically connected to the electrode part in the longitudinal direction In a sensor element comprising a pair of lead portions that extend and narrower than the electrode portion,
It is located between the electrode part and the lead part, and has a connection part for connecting the electrode part and the lead part,
The width of the lead portion is less than 50% of the width of the electrode portion,
Wherein both side surfaces of the connecting portion, when viewed the sensor element along the stacking direction, Ri rounded surface der that is convex on the inside of the above radius 0.4 mm,
Of the longitudinal direction, when the electrode portion is disposed on the tip side, and the lead portion is disposed on the rear end side,
The sensor element according to claim 1, wherein an outer side surface provided on a front end side in the longitudinal direction among both side surfaces of the connection portion is positioned on a front end side with respect to a rear end of the electrode portion . The sensor element according to claim 1, wherein
The sensor element, wherein the electrode part and the lead part are arranged in different ranges in the short direction of the solid electrolyte layer perpendicular to the longitudinal direction.

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