Sensor element and gas sensor

Abstract

To prevent deterioration in specific gas concentration detection accuracy.SOLUTION: A sensor element 101 is provided, comprising an element body 102 having an oxygen ion-conductive solid-state electrolyte layer, a measurement electrode 44 provided inside the element body 102, and a conductive part 74 having an inner lead part 77, a side lead part 78, and a connector electrode 75a, all connected to the measurement electrode 44 in the described order. The inner lead part 77 has a lead-out part 77e acting as an exit from the inside of the element body 102 to a third face 102c. The side lead part 78 connected to the lead-out part 77e is gas permeable. An outer periphery of the lead-out part 77e has an outer periphery length less than 1.30 mm, the outer periphery length being a first outer periphery length of a portion covered with the gas-permeable side lead part 78.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a sensor element and a gas sensor.

Background Art

[0002] Conventionally, a gas sensor including a sensor element for detecting the concentration of a specific gas such as NOx in a gas to be measured such as exhaust gas of an internal combustion engine has been known (see, for example, Patent Document 1). The sensor element of Patent Document 1 includes an element body, an inner electrode, a terminal portion, and a lead portion. The element body has an oxygen ion conductive solid electrolyte layer, and is columnar extending along the longitudinal direction, and has a front end and a rear end which are both ends along the longitudinal direction, and a side surface which is a surface along the longitudinal direction. The front end side of the element body is exposed to the gas to be measured. The inner electrode is disposed inside the element body. The terminal portion is disposed on the rear end side of the side surface of the element body. The lead portion is arranged to connect the inner electrode and the terminal portion, and has an inner portion disposed inside the element body and a side surface conduction portion exposed from the element body on the side surface.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such a sensor element, some gas outside the sensor element (element body) may enter the inside of the element body from the gap between the outer periphery of the end portion on the side surface conduction portion side of the inner portion in the lead portion and the element body, move along the gap between the inner portion and the element body to the inner electrode side, and reach the inner electrode. When such a gas reaches the inner electrode, it may cause a decrease in the detection accuracy of the concentration of the specific gas.

[0005] The sensor element and gas sensor of the present invention mainly aim to suppress a decrease in the detection accuracy of the concentration of a specific gas.

Means for Solving the Problems

[0006] The sensor element and gas sensor of the present invention have adopted the following means to achieve the above main object.

[0007] [1] The sensor element of the present invention is a sensor element for detecting the concentration of a specific gas in a gas to be measured, having an oxygen ion conductive solid electrolyte layer and being columnar extending along the longitudinal direction, having a front end and a rear end which are both ends along the longitudinal direction and a side surface which is a surface along the longitudinal direction, and the front end side being exposed to the gas to be measured, an element body; an inner electrode disposed inside the element body; a conduction part having an inner conduction part disposed inside the element body and conducting with the inner electrode, an outer conduction part disposed on the side surface and having a connector electrode disposed on the rear end side of the side surface and conducting with the inner conduction part; and comprising the inner conduction part having a lead-out part which is an outlet part from the inside of the element body to the side surface, the outer conduction part having a connection part connected to the lead-out part of the inner conduction part, the connection part of the outer conduction part having gas permeability, and / or at least a part of the lead-out part of the inner conduction part being exposed to the outside of the sensor element, for the outer periphery of the lead-out part of the inner conduction part, the outer periphery length which is the sum of the first outer periphery length of the part covered by the connection part having gas permeability and the second outer periphery length of the part exposed to the outside of the sensor element is less than 1.30 mm. This is the gist.

[0008] In the sensor element of the present invention, a connection portion of the outer conduction portion that is connected to the lead-out portion of the inner conduction portion has gas permeability, and / or at least a part of the lead-out portion of the inner conduction portion is exposed to the outside of the sensor element. And, regarding the outer periphery of the lead-out portion of the inner conduction portion, the outer periphery length, which is the sum of the first outer periphery length of the portion covered by the connection portion having gas permeability and the second outer periphery length of the portion exposed to the outside of the sensor element, is less than 1.30 mm. Thereby, it is possible to suppress any gas outside the sensor element (element body) from entering the inside of the element body through the gap between the outer periphery of the lead-out portion of the inner conduction portion and the element body, and it is possible to suppress such gas from reaching the inner electrode. As a result, it is possible to suppress a decrease in the detection accuracy of the concentration of a specific gas. The inventors confirmed this through experiments, analysis, etc.

[0009] [2] In the sensor element of the present invention (the sensor element described in [1] above), the outer periphery length may be 1.15 mm or less. By doing so, it is possible to further suppress any gas outside the sensor element (element body) from entering the inside of the element body through the gap between the outer periphery of the lead-out portion of the inner conduction portion and the element body.

[0010] [3] In the sensor element of the present invention (the sensor element described in [1] or [2] above), the area of the portion of the lead-out portion of the inner conduction portion covered by the connection portion of the outer conduction portion may be 0.0011 mm 2 or more. By doing so, it is possible to suppress the current density of the current flowing through the outer conduction portion and the inner conduction portion from becoming too high. Thereby, it is possible to suppress the heat generation of the lead-out portion and / or the connection portion due to the high current density, and suppress the connection portion from peeling off due to thermal expansion caused by heat generation. The inventors confirmed this through experiments, analysis, etc.

[0011] [4] In the sensor element of the present invention (the sensor element described in [3] above), the area may be 0.0012 mm 2 or more. By doing so, it is possible to further suppress the connection portion from peeling off due to thermal expansion caused by heat generation.

[0012] [5] In the sensor element of the present invention (the sensor element described in any one of [1] to [4] above), the inner electrode may be a measurement electrode used for detecting the concentration of the specific gas.

[0013] [6] In the sensor element of the present invention (the sensor element described in any one of [1] to [5] above), the element body is a laminate in which a plurality of layers including the solid electrolyte layer are laminated in a stacking direction orthogonal to the longitudinal direction, and the laminate has, as the side surfaces, a first surface and a second surface which are both end surfaces in the stacking direction, and a third surface and a fourth surface which are both end surfaces in a direction orthogonal to the longitudinal direction and the stacking direction. The inner conduction part has an inner lead part having a lead-out part which is an outlet part to the third surface or the fourth surface, and the connection part may be a side lead part disposed on the third surface or the fourth surface and connected to the lead-out part.

[0014] [7] In the sensor element of the present invention (the sensor element described in any one of [1] to [5] above), the element body is a laminate in which a plurality of layers including the solid electrolyte layer are laminated in a stacking direction orthogonal to the longitudinal direction, and the laminate has, as the side surfaces, a first surface and a second surface which are both end surfaces in the stacking direction. The element body includes an opening that opens at the first surface or the second surface on the rear end side of the side surface, and has a through hole that penetrates one or more of the plurality of layers in the stacking direction. The inner conduction part has a through hole conductor disposed in the through hole and having a lead-out part which is an outlet part to the opening, and the connection part may be the connector electrode and connected to the lead-out part of the through hole conductor.

[0015] [8] The sensor element of the present invention (the sensor element described in any one of [1] to [7] above) may be used for a gas sensor including the sensor element, a case which is cylindrical and extends along the longitudinal direction of the sensor element and has a second front end and a second rear end which are both ends along the longitudinal direction, and in which the sensor element is disposed inside, and a sealing member for sealing the second rear end side of the case.

[0016] [9] The gas sensor of the present invention includes the sensor element described in any one of [1] to [7] above, a cylindrical case that extends along the longitudinal direction of the sensor element and has a second front end and a second rear end that are both ends along the longitudinal direction, and the sensor element is disposed inside, and a sealing member that seals the second rear end side of the case. The gist of the present invention is to provide such a gas sensor.

[0017] Since the gas sensor of the present invention includes the above-described sensor element, it can achieve the same effects as those achieved by the above-described sensor element, for example, suppressing the arrival of any gas outside the sensor element (element body) at the inner electrode and suppressing a decrease in the detection accuracy of the concentration of a specific gas. Here, examples of any gas outside the sensor element include, for example, a gas generated from the sealing member (for example, a volatile organic gas generated from a rubber stopper as the sealing member).

Brief Description of the Drawings

[0018]

Figure 1

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Figure 11

Embodiments for Carrying Out the Invention

[0019] Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of a gas sensor 100 according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view schematically showing an example of the configuration of a sensor element 101 included in the gas sensor 100. FIG. 3 is a block diagram showing the electrical connection relationship between the control device 95, each cell of the sensor element 101, and the heater 71a. FIG. 4 is a perspective view of the periphery of the rear end portion of the element body 102 of the sensor element 101. FIG. 5 is a partial cross-sectional view showing an enlarged view of the measurement electrode 44 of the sensor element 101 and the periphery of the conduction portion 74 corresponding thereto. The sensor element 101 has an element body 102 having a long rectangular parallelepiped shape. The longitudinal direction (left-right direction in FIG. 2) of the element body 102 is defined as the front-rear direction, the thickness direction (up-down direction in FIG. 2) of the element body 102 is defined as the up-down direction, and the width direction (a direction perpendicular to the front-rear direction and the up-down direction) of the element body 102 is defined as the left-right direction. Since the element body 102 is a rectangular parallelepiped, as shown in FIGS. 2, 4, and 5, as the outer surface of the solid electrolyte layer of the element body 102, there are six surfaces: a first surface 102a (upper surface), a second surface 102b (lower surface), a third surface 102c (left side surface), a fourth surface 102d (right side surface), a fifth surface 102e (front end surface), and a sixth surface 102f (rear end surface).

[0020] As shown in FIG. 1, the gas sensor 100 includes a sensor element 101 having an element body 102, a protective cover 130 that protects the front end side of the element body 102, and a sensor assembly 140 having a connector 150 that conducts with the sensor element 101. This gas sensor 100 is attached to a pipe 190 such as an exhaust gas pipe of an internal combustion engine (such as a diesel engine or a gasoline engine) of a vehicle, for example, as shown in the drawing, and the exhaust gas of the internal combustion engine is used as the gas to be measured, and the concentration of a specific gas such as NOx, O 2 in the gas to be measured, ammonia, etc., is measured (detected). In the present embodiment, the gas sensor 100 is configured to measure the NOx concentration as the specific gas concentration.

[0021] The protective cover 130 includes a bottomed cylindrical inner protective cover 131 that covers the front end portion of the element body 102, and a bottomed cylindrical outer protective cover 132 that covers the inner protective cover 131. A plurality of holes are formed in the inner protective cover 131 and the outer protective cover 132 for allowing the gas to be measured to flow into the protective cover 130. A sensor element chamber 133 is formed as a space surrounded by the inner protective cover 131, and the front end portion of the element body 102 is disposed in the sensor element chamber 133.

[0022] The sensor assembly 140 includes an element sealing body 141 that seals and fixes the sensor element 101, bolts 147 and an outer cylinder 148 attached to the element sealing body 141, and a connector 150 that contacts and is electrically connected to the connector electrodes 75 formed on the surfaces (upper and lower surfaces) of the rear end portion of the element body 102 of the sensor element 101.

[0023] The element sealing body 141 includes a cylindrical main fitting 142, a cylindrical inner cylinder 143 that is welded and fixed coaxially with the main fitting 142, and ceramics supporters 144a to 144c, pressure powders 145a, 145b, and a metal ring 146 enclosed in the through holes inside the main fitting 142 and the inner cylinder 143. The sensor element 101 is located on the central axis of the element sealing body 141 and penetrates the element sealing body 141 in the front-rear direction. The inner cylinder 143 is formed with a reduced diameter portion 143a for pressing the pressure powder 145b in the central axis direction of the inner cylinder 143, and a reduced diameter portion 143b for pressing the ceramics supporters 144a to 144c and the pressure powders 145a, 145b forward via the metal ring 146. Due to the pressing forces from the reduced diameter portions 143a and 143b, the pressure powders 145a, 145b are compressed between the main fitting 142, the inner cylinder 143, and the sensor element 101, thereby sealing between the sensor element chamber 133 in the protective cover 130 and the space 149 in the outer cylinder 148 and fixing the sensor element 101.

[0024] The bolt 147 is fixed coaxially with the main body fitting 142, and has a male screw portion formed on its outer peripheral surface. The male screw portion of the bolt 147 is inserted into a fixing member 191 that is welded to the pipe 190 and has a female screw portion provided on its inner peripheral surface. As a result, the gas sensor 100 is fixed to the pipe 190 in a state where the front end portion of the element body 102 of the sensor element 101 and the protection cover 130 of the gas sensor 100 protrude into the pipe 190.

[0025] The outer cylinder 148 covers the inner cylinder 143, the sensor element 101, and the connector 150, and a plurality of lead wires 155 connected to the connector 150 are drawn out to the outside from the rear end. These lead wires 155 are electrically connected to the respective electrodes (described later) of the sensor element 101 via the connector 150. On the rear end side of the outer cylinder 148, the gap between the outer cylinder 148 and the lead wires 155 is sealed by a rubber plug 157. The outer cylinder 148 is formed with caulking portions 148a and 148b for restricting the relative movement of the rubber plug 157 in the front-rear direction with respect to the outer cylinder 148. The space 149 inside the outer cylinder 148 is filled with a reference gas. The rear end portion of the element body 102 of the sensor element 101 is disposed inside the space 149.

[0026] As shown in FIG. 2, the sensor element 101 includes an element body 102, cells 21, 41, 50, 80 to 83, and a heater portion 70. The element body 102 is a laminate in which six layers, namely, a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, a spacer layer 5, and a second solid electrolyte layer 6, each made of an oxygen ion-conductive solid electrolyte layer such as zirconia (ZrO 2 ) etc., are laminated in this order from the lower side in a plan view. Further, the solid electrolyte forming these six layers is dense and airtight. The element body 102 is manufactured, for example, by performing predetermined processing and printing of circuit patterns on ceramic green sheets corresponding to each layer, then laminating them and further firing them to integrate them.

[0027] On the front end side of the element body 102, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, there are a gas inlet 10, a first diffusion rate-limiting part 11, a buffer space 12, a second diffusion rate-limiting part 13, a first internal cavity (oxygen concentration adjustment chamber) 20, a third diffusion rate-limiting part 30, a second internal cavity (oxygen concentration adjustment chamber) 40, a fourth diffusion rate-limiting part 60, and a third internal cavity (measurement chamber) 61, which are adjacently formed in a communicating manner in this order.

[0028] The gas inlet 10, the buffer space 12, the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 are spaces inside the sensor element 101 that are provided in a manner of punching out the spacer layer 5, with the upper part being the lower surface of the second solid electrolyte layer 6, the lower part being the upper surface of the first solid electrolyte layer 4, and the side part being partitioned by the side surface of the spacer layer 5.

[0029] The first diffusion rate-limiting part 11, the second diffusion rate-limiting part 13, and the third diffusion rate-limiting part 30 are all provided as two horizontally long slits (the opening has a longitudinal direction in the direction perpendicular to the drawing). Also, the fourth diffusion rate-limiting part 60 is provided as one horizontally long slit (the opening has a longitudinal direction in the direction perpendicular to the drawing) formed as a gap with the lower surface of the second solid electrolyte layer 6. Note that the part from the gas inlet 10 to the third internal cavity 61 is also referred to as the measured gas flow-through part.

[0030] The element body 102 is provided with a reference gas introduction part 49 for flowing a reference gas for measuring the NOx concentration to the reference electrode 42 from the outside of the element body 102. The reference gas introduction part 49 has a reference gas introduction space 43 and a reference gas introduction layer 48. The reference gas introduction space 43 is a space provided so as to extend from the sixth surface 102f (rear end surface) of the element body 102 toward the fifth surface 102e (front end surface) side. The reference gas introduction space 43 is provided between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5 and at a position where the side part is partitioned by the side surface of the first solid electrolyte layer 4. The reference gas introduction space 43 opens to the rear end surface of the element body 102, and this opening functions as an inlet part 49a of the reference gas introduction part 49. The reference gas is introduced into the reference gas introduction space 43 from this inlet part 49a. The reference gas introduction part 49 introduces the reference gas introduced from the inlet part 49a to the reference electrode 42 while imparting a predetermined diffusion resistance to the reference gas. The reference gas is air in this embodiment.

[0031] The reference gas introduction layer 48 is provided between the upper surface of the third substrate layer 3 and the lower surface of the first solid electrolyte layer 4. The reference gas introduction layer 48 is a porous body made of ceramics such as alumina, for example. A part of the upper surface of the reference gas introduction layer 48 is exposed in the reference gas introduction space 43. The reference gas introduction layer 48 is formed so as to cover the reference electrode 42. The reference gas introduction layer 48 allows the reference gas to flow from the reference gas introduction space 43 to the reference electrode 42.

[0032] The reference electrode 42 is an electrode formed in a manner sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4. As described above, a reference gas introduction layer 48 connected to the reference gas introduction space 43 is provided around it. Further, as will be described later, it is possible to measure the oxygen concentration (oxygen partial pressure) in the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 using the reference electrode 42.

[0033] In the measured gas flow path, the gas inlet 10 is a part that opens to the external space, and the measured gas is taken into the sensor element 101 from the external space through the gas inlet 10. The first diffusion rate-limiting part 11 is a part that imparts a predetermined diffusion resistance to the measured gas taken in from the gas inlet 10. The buffer space 12 is a space provided to guide the measured gas introduced from the first diffusion rate-limiting part 11 to the second diffusion rate-limiting part 13. The second diffusion rate-limiting part 13 is a part that imparts a predetermined diffusion resistance to the measured gas introduced from the buffer space 12 into the first internal cavity 20. When the measured gas is introduced from outside the sensor element 101 into the first internal cavity 20, the measured gas suddenly taken into the sensor element 101 from the gas inlet 10 due to the pressure fluctuation of the measured gas in the external space (when the measured gas is the exhaust gas of an internal combustion engine, the pulsation of the exhaust pressure) is not directly introduced into the first internal cavity 20, but after the pressure fluctuation of the measured gas is canceled through the first diffusion rate-limiting part 11, the buffer space 12, and the second diffusion rate-limiting part 13, it is introduced into the first internal cavity 20. As a result, the pressure fluctuation of the measured gas introduced into the first internal cavity 20 becomes negligible. The first internal cavity 20 is provided as a space for adjusting the oxygen partial pressure in the measured gas introduced through the second diffusion rate-limiting part 13. This oxygen partial pressure is adjusted by the operation of the main pump cell 21.

[0034] The main pump cell 21 includes an inner pump electrode 22 having a ceiling electrode part 22a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, an outer pump electrode 23 provided in a manner exposed to the outside of the element body 102 in a region corresponding to the ceiling electrode part 22a on the upper surface of the second solid electrolyte layer 6, and the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4 that form a current path between these electrodes, and is an electrochemical pump cell constituted thereby.

[0035] The inner pump electrode 22 is formed across the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that partition the first internal cavity 20, and the spacer layer 5 that provides side walls. Specifically, a ceiling electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that provides the ceiling surface of the first internal cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 that provides the bottom surface of the first internal cavity 20. Then, a side electrode portion (not shown) is formed on the side wall surface (inner surface) of the spacer layer 5 that constitutes both side wall portions of the first internal cavity 20 so as to connect the ceiling electrode portion 22a and the bottom electrode portion 22b, and is disposed in a structure in a tunnel form at the disposition site of the side electrode portion.

[0036] In the main pump cell 21, a desired voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, and a pump current Ip0 is caused to flow in the positive or negative direction between the inner pump electrode 22 and the outer pump electrode 23, so that oxygen in the first internal cavity 20 can be pumped out to the external space, or oxygen in the external space can be pumped into the first internal cavity 20.

[0037] Also, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere in the first internal cavity 20, an electrochemical sensor cell, that is, a main pump control oxygen partial pressure detection sensor cell 80 is constituted by the inner pump electrode 22, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42.

[0038] By measuring the electromotive force (voltage V0) in the main pump control oxygen partial pressure detection sensor cell 80, the oxygen concentration (oxygen partial pressure) in the first internal cavity 20 can be known. Further, the pump current Ip0 is controlled by feedback-controlling the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value. Thereby, the oxygen concentration in the first internal cavity 20 can be maintained at a predetermined constant value.

[0039] The third diffusion rate-limiting part 30 is a part that imparts a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 21 in the first internal cavity 20, and guides the gas to be measured to the second internal cavity 40.

[0040] The second internal cavity 40 is provided as a space for further adjusting the oxygen partial pressure of the gas to be measured introduced through the third diffusion rate-limiting part 30, after the oxygen concentration (oxygen partial pressure) has been adjusted in the first internal cavity 20 in advance, by means of the auxiliary pump cell 50. As a result, the oxygen concentration in the second internal cavity 40 can be kept constant with high precision, so that highly accurate NOx concentration measurement can be performed in the gas sensor 100.

[0041] The auxiliary pump cell 50 includes an auxiliary pump electrode 51 having a ceiling electrode part 51a provided substantially over the entire lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40, an outer pump electrode 23 (not limited to the outer pump electrode 23, and any appropriate electrode disposed on the outer peripheral surface of the element body 102 will suffice), and an auxiliary electrochemical pump cell constituted by the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4.

[0042] The auxiliary pump electrode 51 is disposed in the second internal cavity 40 in a structure having a tunnel form similar to that of the inner pump electrode 22 provided in the first internal cavity 20. That is, on the second solid electrolyte layer 6 that provides the ceiling surface of the second internal cavity 40, a ceiling electrode part 51a is formed, and on the first solid electrolyte layer 4 that provides the bottom surface of the second internal cavity 40, a bottom electrode part 51b is formed, and side electrode parts (not shown) connecting the ceiling electrode part 51a and the bottom electrode part 51b are formed in a tunnel form on both wall surfaces of the spacer layer 5 that provides the side walls of the second internal cavity 40.

[0043] In the auxiliary pump cell 50, by applying a desired voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23, oxygen in the atmosphere within the second internal cavity 40 can be pumped out to the external space or pumped into the second internal cavity 40 from the external space.

[0044] Also, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an electrochemical sensor cell, that is, an oxygen partial pressure detection sensor cell 81 for auxiliary pump control, is formed by the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, and the third substrate layer 3.

[0045] Note that the auxiliary pump cell 50 pumps based on the electromotive force (voltage V1) detected by this oxygen partial pressure detection sensor cell 81 for auxiliary pump control by a variable power supply 52 whose voltage is controlled. As a result, the oxygen partial pressure in the atmosphere within the second internal cavity 40 is controlled to a low partial pressure that has substantially no influence on the measurement of NOx.

[0046] At the same time, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor cell 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor cell 80 for main pump control, and by controlling the above-described target value of its voltage V0, the gradient of the oxygen partial pressure in the measurement gas introduced from the third diffusion rate-limiting section 30 into the second internal cavity 40 is always kept constant. When used as a NOx sensor, due to the functions of the main pump cell 21 and the auxiliary pump cell 50, the oxygen concentration within the second internal cavity 40 is maintained at a constant value of about 0.001 ppm.

[0047] The fourth diffusion rate-limiting section 60 is a site that imparts a predetermined diffusion resistance to the measurement gas whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump cell 50 in the second internal cavity 40 and guides the measurement gas to the third internal cavity 61. The fourth diffusion rate-limiting section 60 plays a role in limiting the amount of NOx flowing into the third internal cavity 61.

[0048] The third internal space 61 is provided as a space for performing a process related to the measurement of the nitrogen oxide (NOx) concentration in the gas to be measured, which is introduced through the fourth diffusion rate-limiting section 60, after the oxygen concentration (oxygen partial pressure) has been adjusted in the second internal space 40 in advance. The measurement of the NOx concentration is mainly performed in the third internal space 61 by the operation of the measurement pump cell 41.

[0049] The measurement pump cell 41 measures the NOx concentration in the gas to be measured within the third internal space 61. The measurement pump cell 41 is an electrochemical pump cell composed of a measurement electrode 44 provided on the upper surface of the first solid electrolyte layer 4 facing the third internal space 61, an outer pump electrode 23, a second solid electrolyte layer 6, a spacer layer 5, and the first solid electrolyte layer 4. The measurement electrode 44 also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere within the third internal space 61.

[0050] In the measurement pump cell 41, oxygen generated by the decomposition of nitrogen oxide (NOx) in the atmosphere around the measurement electrode 44 can be pumped out, and the generated amount can be detected as a pump current Ip2.

[0051] Also, in order to detect the oxygen partial pressure around the measurement electrode 44, an electrochemical sensor cell, that is, an oxygen partial pressure detection sensor cell 82 for controlling the measurement pump, is constituted by the first solid electrolyte layer 4, the third substrate layer 3, the measurement electrode 44, and the reference electrode 42. The variable power supply 46 is controlled based on the electromotive force (voltage V2) detected by the oxygen partial pressure detection sensor cell 82 for controlling the measurement pump.

[0052] The gas to be measured introduced into the second internal space 40 reaches the measurement electrode 44 within the third internal space 61 through the fourth diffusion rate-limiting section 60 under the condition that the oxygen partial pressure is controlled. The nitrogen oxide (NOx) in the gas to be measured around the measurement electrode 44 is reduced (2NO → N 2 +O 2) Oxygen is generated. Then, the generated oxygen is pumped by the measurement pump cell 41. At this time, the voltage Vp2 of the variable power supply 46 is controlled so that the voltage V2 detected by the oxygen partial pressure detection sensor cell 82 for controlling the measurement pump becomes constant (target value). Since the amount of oxygen generated around the measurement electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured, the concentration of nitrogen oxides in the gas to be measured is calculated using the pump current Ip2 in the measurement pump cell 41.

[0053] Also, if the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 are combined to form oxygen partial pressure detection means as an electrochemical sensor cell, the electromotive force corresponding to the difference between the amount of oxygen generated by the reduction of the NOx component in the atmosphere around the measurement electrode 44 and the amount of oxygen contained in the reference atmosphere can be detected, and thereby the concentration of the NOx component in the gas to be measured can also be obtained.

[0054] Furthermore, an electrochemical sensor cell 83 is constituted by the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42. The oxygen partial pressure in the gas to be measured around the outer pump electrode 23, specifically, outside the element body 102 of the sensor element 101 can be detected by the electromotive force (voltage Vref) obtained by this sensor cell 83.

[0055] In the gas sensor 100 having such a configuration, the gas to be measured in which the oxygen partial pressure is always maintained at a constant low value (a value that has substantially no influence on the measurement of NOx) is supplied to the measurement pump cell 41 by operating the main pump cell 21 and the auxiliary pump cell 50. Therefore, based on the pump current Ip2 flowing by pumping out the oxygen generated by the reduction of NOx from the measurement pump cell 41 in proportion to the concentration of NOx in the gas to be measured, the concentration of NOx in the gas to be measured can be known.

[0056] Here, each of the electrodes 22, 23, 42, 44, 51 will be described. The inner pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44 each contain a first noble metal having catalytic activity. Examples of the first noble metal include at least any one of Pt, Rh, Ir, Ru, and Pd. The outer pump electrode 23 and the reference electrode 42 also contain the first noble metal. The inner pump electrode 22 and the auxiliary pump electrode 51 also contain a second noble metal that suppresses the catalytic activity for a specific gas (NOx) by the first noble metal. Thereby, the reduction ability of the inner pump electrode 22 and the auxiliary pump electrode 51 with respect to the NOx component in the gas to be measured is weakened. Examples of the second noble metal include Au. The measurement electrode 44 does not contain the second noble metal. Thereby, the reduction ability with respect to the NOx component in the gas to be measured is enhanced compared to the inner pump electrode 22 and the auxiliary pump electrode 51. The measurement electrode 44 preferably contains at least one of Pt and Rh among the first noble metals, and may contain both Pt and Rh. It is also preferable that the outer pump electrode 23 and the reference electrode 42 do not contain the second noble metal. Each of the electrodes 22, 23, 42, 44, 51 is preferably a cermet containing a noble metal and an oxide having oxygen ion conductivity (for example, ZrO 2 ). Each of the electrodes 22, 23, 42, 44, 51 is preferably a porous body. In the present embodiment, the inner pump electrode 22 and the auxiliary pump electrode 51 are made of a porous cermet electrode of Pt containing 1% Au and ZrO 2 . Also, both the outer pump electrode 23 and the reference electrode 42 are made of a porous cermet electrode of Pt and ZrO 2 . The measurement electrode 44 is made of a porous cermet electrode of Pt, Rh, and ZrO 2 .

[0057] The heater unit 70 plays a role of temperature adjustment for heating and keeping warm the sensor element 101 in order to enhance the oxygen ion conductivity of the solid electrolyte of the element body 102. The heater unit 70 includes a heater 71a, a heater insulating layer 71b, and a pressure release hole 71c.

[0058] The heater 71a is an electric resistor formed in a manner of being sandwiched from above and below by the second substrate layer 2 and the third substrate layer 3. When the heater 71a is powered by the heater power supply 72, it generates heat to heat and keep warm the solid electrolyte of the element body 102 of the sensor element 101. Further, the heater 71a is embedded across the entire area from the first internal cavity 20 to the third internal cavity 61, and it is possible to adjust the entire sensor element 101 to a temperature at which the solid electrolyte is activated.

[0059] The heater insulating layer 71b is an insulating layer formed of an insulator such as alumina on the upper and lower surfaces of the heater 71a. The heater insulating layer 71b is formed for the purpose of obtaining electrical insulation between the second substrate layer 2 and the heater 71a, and electrical insulation between the third substrate layer 3 and the heater 71a.

[0060] The pressure dissipation hole 71c is a portion provided so as to penetrate the third substrate layer 3 and the reference gas introduction layer 48 and communicate with the reference gas introduction space 43, and is formed for the purpose of alleviating the increase in internal pressure accompanying the increase in temperature within the heater insulating layer 71b.

[0061] The gas sensor 100 further includes a control device 95. As shown in FIG. 3, the control device 95 includes the variable power supplies 24, 46, 52 described above, the heater power supply 72 described above, and a control unit 96. The control unit 96 is a microprocessor having a CPU 97 and a storage unit 98. The storage unit 98 is a non-volatile memory capable of rewriting information, and can store various programs and various data, for example. The control unit 96 inputs the voltage V0 of the oxygen partial pressure detection sensor cell 80 for main pump control, the voltage V1 of the oxygen partial pressure detection sensor cell 81 for auxiliary pump control, the voltage V2 of the oxygen partial pressure detection sensor cell 82 for measurement pump control, the voltage Vref of the sensor cell 83, the pump current Ip0 flowing through the main pump cell 21, the pump current Ip1 flowing through the auxiliary pump cell 50, and the pump current Ip2 flowing through the measurement pump cell 41. Further, the control unit 96 controls the voltages Vp0, Vp1, Vp2 output by the variable power supplies 24, 46, 52 by outputting a control signal to the variable power supplies 24, 46, 52, thereby controlling the main pump cell 21, the measurement pump cell 41, and the auxiliary pump cell 50. The control unit 96 controls the power supplied by the heater power supply 72 to the heater 71a by outputting a control signal to the heater power supply 72. The storage unit 98 also stores target values V0*, V1*, V2* and the like, which will be described later. The CPU 97 of the control unit 96 controls each pump cell 21, 41, 50 with reference to these target values V0*, V1*, V2*.

[0062] The control unit 96 performs an auxiliary pump control process for controlling the auxiliary pump cell 50 so that the oxygen concentration in the second internal cavity 40 becomes the target concentration. Specifically, the control unit 96 controls the auxiliary pump cell 50 by feedback-controlling the voltage Vp1 of the variable power supply 52 so that the voltage V1 becomes a constant value (referred to as the target value V1*). The target value V1* is determined as a value such that the oxygen concentration in the second internal cavity 40 becomes a predetermined low concentration that has substantially no influence on the measurement of NOx.

[0063] The control unit 96 performs main pump control processing to control the main pump cell 21 so that the pump current Ip1 flowing when the auxiliary pump cell 50 adjusts the oxygen concentration in the second internal cavity 40 becomes the target current (referred to as the target value Ip1*). Specifically, the control unit 96 sets (feedback control) the target value (referred to as the target value V0*) of the voltage V0 based on the pump current Ip1 so that the pump current Ip1 flowing due to the voltage Vp1 becomes a constant target value Ip1*. Then, the control unit 96 performs feedback control on the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value V0* (that is, so that the oxygen concentration in the first internal cavity 20 becomes the target concentration). By this main pump control processing, the gradient of the oxygen partial pressure in the measurement gas introduced from the third diffusion rate limiting section 30 into the second internal cavity 40 always becomes constant. The target value V0* is set to a value such that the oxygen concentration in the first internal cavity 20 is higher than 0% and is a low concentration. Also, the pump current Ip0 flowing during this main pump control processing changes according to the oxygen concentration of the measurement gas flowing into the measurement gas flow path from the gas inlet 10 (that is, the measurement gas around the sensor element 101). Therefore, the control unit 96 can also detect the oxygen concentration in the measurement gas based on the pump current Ip0.

[0064] The above-described main pump control processing and auxiliary pump control processing are collectively also referred to as adjustment pump control processing. Also, the first internal cavity 20 and the second internal cavity 40 are collectively also referred to as an oxygen concentration adjustment chamber. The main pump cell 21 and the auxiliary pump cell 50 are collectively also referred to as adjustment pump cells. By the control unit 96 performing the adjustment pump control processing, the adjustment pump cells adjust the oxygen concentration in the oxygen concentration adjustment chamber.

[0065] The control unit 96 performs a measurement pump control process for controlling the measurement pump cell 41 so that the voltage V2 becomes a constant value (referred to as a target value V2*), that is, so that the oxygen concentration in the third internal cavity 61 becomes a predetermined low concentration. Specifically, the control unit 96 controls the measurement pump cell 41 by feedback controlling the voltage Vp2 of the variable power supply 46 so that the voltage V2 becomes the target value V2*. By this measurement pump control process, oxygen is pumped out from the third internal cavity 61.

[0066] By performing the measurement pump control process, oxygen is pumped out from the third internal cavity 61 so that the oxygen generated by the reduction of NOx in the gas to be measured in the third internal cavity 61 becomes substantially zero. Then, the control unit 96 acquires the pump current Ip2 as a detection value corresponding to the oxygen generated in the third internal cavity 61 from a specific gas (here, NOx), and calculates the NOx concentration in the gas to be measured based on this pump current Ip2.

[0067] The storage unit 98 stores a relational expression (for example, an expression of a linear function or a quadratic function) or a map as a correspondence relationship between the pump current Ip2 and the NOx concentration. Such a relational expression or map can be obtained in advance by experiments.

[0068] The control unit 96 performs a heater control process of outputting a control signal to the heater power supply 72 to control the temperature of the heater 71a to reach a target temperature (for example, 800°C). Here, the temperature of the heater 71a can be expressed by a linear function formula of the resistance value of the heater 71a. In the heater control process, the control unit 96 calculates the resistance value of the heater 71a as a value that can be regarded as the temperature of the heater 71a (a value convertible to temperature), and performs feedback control on the heater power supply 72 so that the calculated resistance value becomes the target resistance value (the resistance value corresponding to the target temperature). The control unit 96 can obtain, for example, the voltage of the heater 71a and the current flowing through the heater 71a, and calculate the resistance value of the heater 71a based on the obtained voltage and current. The control unit 96 may calculate the resistance value of the heater 71a by, for example, the three-terminal method or the four-terminal method. When energizing the heater 71a, the heater power supply 72 adjusts the power supplied to the heater 71a by changing the value of the voltage applied to the heater 71a based on, for example, a control signal from the control unit 96.

[0069] Note that including the variable power supplies 24, 46, 52 and the heater power supply 72 shown in FIG. 3, the control device 95 is connected to each of the electrodes 22, 23, 42, 44, 51 and the heater 71a via corresponding conduction parts 74. Each of the plurality of conduction parts 74 has a connector electrode 75 and a lead part 76 for electrically connecting the corresponding electrode and the connector electrode 75 to each other. Although all of the plurality of connector electrodes 75 are shown in FIG. 4, only the lead part 76 corresponding to the measurement electrode 44 is shown for the lead part 76.

[0070] The plurality of connector electrodes 75 each function as a terminal for electrically connecting the sensor element 101 to the outside. As shown in FIG. 4, the plurality of connector electrodes 75 are disposed on the rear end side of the first surface 102a (upper surface) or the second surface 102b (lower surface) of the element body 102 of the sensor element 101. Specifically, the plurality of connector electrodes 75 include connector electrodes 75a to 75d sequentially arranged from the left on the rear end side of the first surface 102a of the element body 102, and connector electrodes 75e to 75h sequentially arranged from the left on the rear end side of the second surface 102b of the element body 102. The connector electrodes 75a to 75d and 75h are each connected to (electrically conduct with) the measurement electrode 44, the outer pump electrode 23, the auxiliary pump electrode 51, the inner pump electrode 22, and the reference electrode 42 via the corresponding lead portion 76. The connector electrodes 75e to 75g are each connected to the heater 71a via the corresponding lead portion 76.

[0071] Here, the details of the measurement electrode 44 and the corresponding conduction portion 74 (connector electrode 75a and lead portion 76) will be described with reference to FIGS. 4 and 5. Although not shown in FIG. 2, an airtight adhesive layer is provided between two adjacent layers in the stacking direction (vertical direction) among the layers 1 to 6 of the element body 102. Therefore, two adjacent layers are adhered by the corresponding adhesive layer. Each adhesive layer preferably has oxygen ion conductivity, similar to the layers 1 to 6. In this embodiment, each adhesive layer is made of ceramics mainly composed of the same zirconia as the layers 1 to 6. As shown in FIG. 5, among the adhesive layers, the adhesive layer 7 adheres the first solid electrolyte layer 4 and the spacer layer 5. The adhesive layer 7 covers most of the upper surface of the first solid electrolyte layer 4 except for the portions where the measured gas flow portions such as the buffer space 12, the first internal cavity 20, and the second internal cavity 40 are located.

[0072] The measurement electrode 44 is provided on the upper surface of the first solid electrolyte layer 4 facing the third internal cavity 61. The lead portion 76 corresponding to the measurement electrode 44 has an inner lead portion 77 and a side lead portion 78. The inner lead portion 77 is disposed inside the element main body 102 and is connected to (electrically conductive with) the measurement electrode 44 and the side lead portion 78. Specifically, the inner lead portion 77 has first to fourth portions 77a to 77d. The first portion 77a is disposed on the upper surface of the first solid electrolyte layer 4 facing the third internal cavity 61. The right end of the first portion 77a is connected to the measurement electrode 44, and the first portion 77a extends linearly to the left side surface of the third internal cavity 61 along the left - right direction. The right end of the second portion 77b is connected to the left end of the first portion 77a, and the second portion 77b extends linearly to a position in front of the left end of the element main body 102 along the left - right direction. The front end of the third portion 77c is connected to the left end of the second portion 77b, and the third portion 77c extends linearly to the vicinity of the rear end of the element main body 102 along the front - rear direction. The right end of the fourth portion 77d is connected to the rear end of the third portion 77c, and the fourth portion 77d extends linearly to the left end of the element main body 102 along the left - right direction. The lead - out portion 77e, which is the left end portion of the fourth portion 77d, reaches (is led out to) the third surface 102c (left end surface) of the element main body 102. The lead - out portion 77e is the outlet portion of the inner lead portion 77 from the inside of the element main body 102 to the third surface 102c. The lead - out portion 77e is covered by and connected to the side lead portion 78. In the present embodiment, the shape of the left surface of the lead - out portion 77e, that is, the portion covered by the side lead portion 78, is substantially rectangular in a left - surface view as shown by the broken - line frame in FIG. 4. The inner lead portion 77 is a conductor mainly composed of a noble metal such as platinum (Pt) or a high - melting - point metal such as tungsten (W) or molybdenum (Mo). The inner lead portion 77 is preferably a cermet conductor containing a noble metal or a high - melting - point metal and zirconia, which is the same as the main component of the first solid electrolyte layer 4. The inner lead portion 77 preferably has no gas permeability. For example, if the porosity of the inner lead portion 77 is less than 1.5%, it has no gas permeability. More preferably, the porosity of the inner lead portion 77 is 1.0% or less.

[0073] Of the inner lead portion 77, the entire second and third portions 77b and 77c and the portion of the fourth portion 77d other than the lead-out portion 77e are surrounded by the lead insulating layer 79. The lead insulating layer 79 insulates the portion of the inner lead portion 77 that surrounds the outer periphery from the first solid electrolyte layer 4 and the spacer layer 5. Note that the outer periphery of the lead-out portion 77e of the fourth portion 77d is not surrounded by the lead insulating layer 79. Thereby, when manufacturing the sensor element 101, it is possible to suppress the outer periphery of the lead-out portion 77e from being surrounded by the lead insulating layer 79, and to suppress the connection (electrical conduction) between the left surface of the lead-out portion 77e and the side surface lead portion 78 from being inhibited. The lead insulating layer 79 is an insulator of ceramics such as alumina.

[0074] The side surface lead portion 78 has a substantially rectangular parallelepiped shape and is disposed on the rear end side of the third surface 102c of the element body 102, and is connected to the inner lead portion 77 and the connector electrode 75a. Specifically, the side surface lead portion 78 is disposed on the third surface 102c so as to cover the entire lead-out portion 77e of the inner lead portion 77, so that the left surface of the lead-out portion 77e is not exposed to the outside of the sensor element 101. The central portion of the right end surface of the side surface lead portion 78 is connected to the lead-out portion 77e (electrically conductive). The upper end portion of the right end surface of the side surface lead portion 78 is connected to the left end surface of the front end portion of the connector electrode 75a.

[0075] The side surface lead portion 78 is a conductor mainly composed of a noble metal such as platinum (Pt). The side surface lead portion 78 is preferably a conductor containing a noble metal and alumina (Al 2 O 3 ). The side surface lead portion 78 is configured to satisfy Rp / Dc>145% / mm when the porosity is Rp [%] and the thickness is Dc [mm]. Therefore, the side surface lead portion 78 has gas permeability. The inventors confirmed this by experiments, analysis, etc. The porosity Rp of the side surface lead portion 78 may be 1.0% or more. The thickness Dc of the side surface lead portion 78 may be 0.001 mm or more.

[0076] Regarding the outer periphery of the lead-out portion 77e, the outer periphery length L, which is the sum of the first outer periphery length L1 of the portion covered by the side lead portion 78 having gas permeability and the second outer periphery length L2 of the portion exposed outside the sensor element 101, is configured to be less than 1.30 mm. In the present embodiment, as described above, the entire lead-out portion 77e is covered by the side lead portion 78, and since there is no "portion exposed outside the sensor element 101" in the outer periphery of the lead-out portion 77e, the second outer periphery length L2 is 0 mm. Therefore, the first outer periphery length L1, specifically, the length of the broken line indicating the contour of the lead-out portion 77e in FIG. 4, is equal to the outer periphery length L. When some gas outside the sensor element 101 (element body 102) enters the inside of the element body 102 through the gap between the outer periphery of the lead-out portion 77e of the inner lead portion 77 and the element body 102, it moves along the gap between the outer periphery of the inner lead portion 77 and the element body 102 (the gap between the inner lead portion 77 and the adhesive layer 7 or the gap between the inner lead portion 77 and the lead insulating layer 79) to the measurement electrode 44 side and may reach the measurement electrode 44. Examples of some gas outside the sensor element 101 include volatile organic gases generated from the rubber stopper 157 when the sensor element 101 is exposed to a high-temperature environment. When such gas reaches the measurement electrode 44, the oxygen concentration around the measurement electrode 44 decreases, the voltage V2 detected by the oxygen partial pressure detection sensor cell 82 for measurement pump control increases, and the amount of oxygen pumped out from the third internal cavity 61 by the measurement pump control process decreases, and the pump current Ip2 may decrease. The decrease in the pump current Ip2 causes a decrease in the detection accuracy of the concentration of a specific gas (NOx). Based on these considerations, in the present embodiment, the outer periphery length L is configured to be less than 1.30 mm. As a result, since the outer periphery length L (= first outer periphery length L1) of the lead-out portion 77e is short, the gap through which gas can enter between the outer periphery of the lead-out portion 77e and the element body 102 can be reduced. Therefore, it is possible to suppress the entry of any gas outside the element body 102 into the element body 102 and suppress the arrival of such gas at the measurement electrode 44. As a result, it is possible to suppress the decrease in the pump current Ip2 and suppress the decrease in the detection accuracy of the concentration of a specific gas (NOx). The inventors confirmed these things through experiments, analysis, etc.Moreover, by suppressing the arrival of such gas at the measurement electrode 44, deterioration of the measurement electrode 44 can be suppressed. The outer peripheral length L is preferably 1.15 mm or less.

[0077] The area S of the portion of the lead-out portion 77e covered by the side surface lead portion 78 is preferably 0.0011 mm 2 or more. In the present embodiment, as described above, the entire left surface of the lead-out portion 77e is covered by the side surface lead portion 78. Therefore, the area of the entire left surface of the lead-out portion 77e, that is, the area of the portion surrounded by the broken line frame showing the lead-out portion 77e in FIG. 4 is equal to the area S. By this area S being 0.0011 mm 2 or more, it is possible to suppress the current density of the current flowing through the side surface lead portion 78 and the lead-out portion 77e from becoming too high. Thereby, heat generation of the lead-out portion 77e and / or the side surface lead portion 78 due to high current density can be suppressed, and peeling of the side surface lead portion 78 from the third surface 102c of the element body 102 or the lead-out portion 77e due to thermal expansion caused by heat generation can be suppressed. The inventors confirmed this through experiments, analysis, etc. The area S is more preferably 0.0012 mm 2 or more. The area S may be 0.00175 mm 2 or more. The area S may be 0.0018 mm 2 or more. The area S may be 0.0020 mm 2 or more. The area S may be 0.0024 mm 2 or more.

[0078] The lead-out portion 77e may have a width in the front-rear direction of 0.25 mm or more. The lead-out portion 77e may have a width in the front-rear direction of 0.64 mm or less. The lead-out portion 77e may have a thickness of 0.004 mm or more. The lead-out portion 77e may have a thickness of 0.015 mm or less.

[0079] Note that each porosity such as the porosity Rp of the side lead portion 78 is a value derived as follows using an image (SEM image) obtained by observing with a scanning electron microscope (SEM). First, the measurement target is cut so that the cross-section of the measurement target (when the side lead portion 78 is the measurement target, the cross-section along the thickness direction of the side lead portion 78) is the observation surface, and the cut surface is resin-embedded and polished to obtain an observation sample. Subsequently, an SEM photograph (secondary electron image, acceleration voltage 15 kV, magnification 1000 times, but if 1000 times magnification is inappropriate, the magnification is greater than 1000 times and 5000 times or less) is used to photograph the observation surface of the observation sample, thereby obtaining an SEM image of the measurement target. Next, the obtained image is subjected to image analysis, and a threshold value is determined by the discriminant analysis method (Otsu's binarization) from the luminance distribution of the luminance data of the pixels in the image. Thereafter, each pixel in the image is binarized into an object portion and a pore portion based on the determined threshold value, and the area of the object portion and the area of the pore portion are calculated. Then, the ratio of the area of the pore portion to the total area (the total area of the object portion and the pore portion) is derived as the porosity (unit: %).

[0080] Next, an example of a method for manufacturing the sensor element 101 of such a gas sensor 100 will be described below. First, six unfired ceramic green sheets containing an oxygen ion conductive solid electrolyte such as zirconia as a ceramic component are prepared. A plurality of sheet holes and necessary through-holes for positioning during printing or lamination are formed in advance in this green sheet. Further, in the green sheet that will become the spacer layer 5, a space that will become the measured gas flow portion is provided in advance by punching or the like. Similarly, a space that will become the reference gas introduction space 43 is also provided in the green sheet that will become the first solid electrolyte layer 4. Then, for each of the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6, a pattern printing process and a drying process for forming various patterns on each ceramic green sheet are performed. Specifically, the patterns to be formed are, for example, each electrode such as the measurement electrode 44 described above, inner lead portions such as the inner lead portion 77 connected to each electrode, lead insulating layers such as the lead insulating layer 79, connector electrodes 75, reference gas introduction layers 48, patterns such as the heater portion 70. Pattern printing is performed by applying a pattern forming paste prepared according to the characteristics required for each formation target to the green sheet using a known screen printing technique. The drying process is also performed using known drying means. After the pattern printing process and the drying process are completed, a printing process and a drying process of an adhesive paste that will become an adhesive layer (including the adhesive layer 7 described above) for laminating and adhering the green sheets corresponding to each layer are performed. Then, the green sheets on which the adhesive paste is formed are laminated in a predetermined order while being positioned by the sheet holes, and a crimping process is performed by applying predetermined temperature and pressure conditions to form a single laminate. The laminate thus obtained includes a plurality of sensor elements 101. The laminate is cut into the size of the sensor element 101. Then, a pattern that will become the side lead portion 78 is formed by screen printing on the portion that will become the third surface 102c of the element body 102 of the sensor element 101, which is the cut surface of the laminate, and the drying process of this pattern is performed. Then, the laminate is fired at a predetermined firing temperature to obtain the sensor element 101.

[0081] When forming the patterns for the inner lead portion 77 and the lead insulating layer 79 on the green sheet that becomes the first solid electrolyte layer 4, for example, the following method may be used. First, form a pattern on the green sheet that covers the lower side of the inner lead portion 77 in the lead insulating layer 79. Subsequently, form the pattern for the inner lead portion 77. Then, form the portions that cover the sides and the upper side of the inner lead portion 77 in the lead insulating layer 79.

[0082] For the paste for forming the pattern of the inner lead portion 77, a paste containing a noble metal such as platinum is used. It is preferable to use a paste containing a noble metal and zirconia for the paste for forming the pattern of the inner lead portion 77. The adjustment of the porosity of the inner lead portion 77 can be performed, for example, by adjusting the particle size of the particles contained in the paste for forming the pattern of the inner lead portion 77, or by adjusting the firing temperature and firing time when firing the laminate. The adjustment of the outer peripheral length L and the area S of the lead-out portion 77e in the inner lead portion 77 can be performed, for example, by adjusting the width in the front-rear direction of the pattern of the portion that becomes the lead-out portion 77e in the inner lead portion 77, or by adjusting the thickness of the lead-out portion 77e. The thickness of the lead-out portion 77e can be adjusted, for example, by adjusting the viscosity of the paste for forming the pattern of the inner lead portion 77, or by changing the number of printing times during pattern formation.

[0083] Also, for the paste for forming the pattern of the side lead portion 78, a paste containing a noble metal such as platinum is used. It is preferable to use a paste containing a noble metal and alumina for the paste for forming the pattern of the side lead portion 78. The adjustment of the porosity Rp of the side lead portion 78 can be performed, for example, by adjusting the particle size of the particles contained in the paste for forming the pattern of the side lead portion 78, or by adjusting the particle size and content ratio of the pore-forming material, or by adjusting the firing temperature and firing time when firing the laminate. The adjustment of the thickness Dc of the side lead portion 78 can be performed, for example, by adjusting the viscosity of the paste for forming the pattern of the side lead portion 78, or by changing the number of printing times during pattern formation.

[0084] Thereafter, a gas sensor 100 incorporating the sensor element 101 is manufactured. For example, an element sealing body 141 is attached to and sealed and fixed to the sensor element 101, and a protective cover 130 is attached to the tip side of the element main body 102 of the sensor element 101 in the element sealing body 141. Further, a connector 150 and a lead wire 155 are attached to the rear end side of the element main body 102 of the sensor element 101 so as to be electrically connected to the connector electrode 75. Furthermore, an outer cylinder 148 is attached to the rear end side of the element main body 102 in the element sealing body 141, the lead wire 155 is drawn out from the outer cylinder 148 to the outside, and the outer cylinder 148 is welded and fixed to the main fitting 142. Subsequently, the rubber plug 57 is inserted into the outer cylinder 148 through the through hole of the rubber plug 157 with the lead wire 155 passed therethrough, the outer cylinder 148 is reduced in diameter by caulking to form caulked portions 148a and 148b, and the rubber plug 57 and the outer cylinder 148 are fixed. Then, the control device 95 and the sensor element 101 are connected via the lead wire 155. Thereby, the gas sensor 100 is obtained.

[0085] Next, an example of using the gas sensor 100 will be described. First, the CPU 97 of the control unit 96 controls the heater power supply 72 to supply power to the heater 71a so that the temperature of the heater 71a becomes a target temperature (for example, 800°C). The CPU 97 acquires, for example, a value convertible to the temperature of the heater 71a (for example, the resistance value or current value of the heater 71a), and controls the heater power supply 72 based on this value to feedback-control the temperature of the heater 71a. When the temperature of the heater 71a reaches the target temperature (or near the target temperature), the CPU 97 starts controlling each of the above-described pump cells 21, 41, 50 (adjustment pump control process and measurement pump control process) and acquiring each of the voltages V0, V1, V2, Vref from each of the above-described sensor cells 80 to 83. In this state, when the gas to be measured is introduced from the gas inlet 10, the gas to be measured passes through the first diffusion rate-limiting section 11, the buffer space 12, and the second diffusion rate-limiting section 13 and reaches the first internal cavity 20. Next, the oxygen concentration of the gas to be measured is adjusted by the main pump cell 21 and the auxiliary pump cell 50 in the first internal cavity 20 and the second internal cavity 40, and the adjusted gas to be measured reaches the third internal cavity 61. Then, the CPU 97 detects the concentration of NOx in the gas to be measured based on the acquired pump current Ip2 and the correspondence relationship stored in the storage unit 98.

[0086] Here, the correspondence between the components of the present embodiment and the components of the present invention will be clarified. Each of the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6 of the present embodiment corresponds to the solid electrolyte layer of the present invention, the element body 102 corresponds to the element body, the first surface to the fourth surface 102a to 102d correspond to the side surfaces, the measurement electrode 44 corresponds to the inner electrode, the conduction portion 74 corresponds to the conduction portion, the inner lead portion 77 corresponds to the inner conduction portion, the connector electrode 75a and the side surface lead portion 78 correspond to the outer conduction portion, the lead-out portion 77e corresponds to the lead-out portion, and the side surface lead portion 78 corresponds to the connection portion. Further, the protective cover 130 and the sensor assembly 140 correspond to the case, and the rubber stopper 157 corresponds to the sealing member.

[0087] In the sensor element 101 included in the gas sensor 100 of the present embodiment described in detail above, regarding the outer periphery of the lead-out portion 77e of the inner lead portion 77, the first outer periphery length L1 of the portion covered by the connection portion (here, the side lead portion 78) having gas permeability and connected to the lead-out portion 77e and the second outer periphery length L2 of the portion exposed to the outside of the sensor element 101, the outer periphery length L, which is the sum of these, is less than 1.30 mm. Thereby, it is possible to suppress any gas outside the sensor element 101 (element main body 102) from entering the inside of the element main body 102 through the gap between the outer periphery of the lead-out portion 77e of the inner lead portion 77 and the element main body 102, and it is possible to suppress such gas from reaching the measurement electrode 44. As a result, it is possible to suppress a decrease in the pump current Ip2 and suppress a decrease in the detection accuracy of the concentration of a specific gas (NOx).

[0088] Further, in the sensor element 101, the outer periphery length L of the lead-out portion 77e is 1.15 mm or less. Thereby, it is possible to further suppress any gas outside the element main body 102 from entering the inside of the element main body 102 through the gap between the outer periphery of the lead-out portion 77e and the element main body 102.

[0089] Furthermore, in the sensor element 101, the area S of the portion of the lead-out portion 77e of the inner lead portion 77 covered by the side lead portion 78 is 0.0011 mm 2 or more. Thereby, it is possible to suppress the current density of the current flowing through the side lead portion 78 and the lead-out portion 77e from becoming too high. Therefore, it is possible to suppress heat generation of the lead-out portion 77e and / or the side lead portion 78 due to a high current density, and suppress peeling of the side lead portion 78 due to thermal expansion caused by heat generation.

[0090] In addition, in the sensor element 101, the area S of the lead-out portion 77e is 0.0012 mm 2 or more. Thereby, it is possible to further suppress peeling of the side lead portion 78 due to thermal expansion caused by heat generation.

[0091] Note that the present invention is not limited to the above-described embodiment at all, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

[0092] For example, in the above-described embodiment, the lead-out portion 77e was entirely covered by the side lead portion 78 and was not exposed outside the sensor element 101, but the present invention is not limited to this. It is sufficient that the side lead portion 78 has gas permeability and / or at least a part of the lead-out portion 77e of the inner lead portion 77 is exposed outside the sensor element 101. For example, as shown in the sensor element 201 of the modification example in FIG. 6, the inner lead portion 77 may be replaced with the inner lead portion 277 and the side lead portion 78 may be replaced with the side lead portion 278. The lead-out portion 277e, which is the left end portion of the fourth portion 277d of the inner lead portion 277, has a portion covered by the side lead portion 278 and a portion protruding forward from the side lead portion 278 and exposed outside the sensor element 101.

[0093] In the sensor element 201 of FIG. 6, when the connection portion (here, the side lead portion 278) has gas permeability in the same manner as the side lead portion 78, the length of the portion indicated by the broken line in FIG. 6 of the outer periphery of the lead-out portion 277e of the inner lead portion 277 is the first outer peripheral length L1 of the portion covered by the side lead portion 278. Also, the length of the portion indicated by the solid line in FIG. 6 of the outer periphery of the lead-out portion 277e is the second outer peripheral length L2 of the portion exposed outside the sensor element 101. And the sum of these first outer peripheral length L1 and second outer peripheral length L2 is the outer peripheral length L. The outer peripheral length L in this case is equal to the outer peripheral length of the lead-out portion 277e. Regarding this outer peripheral length L, it may be configured in the same manner as the sensor element 101, for example, so as to be less than 1.30 mm.

[0094] In the sensor element 201 of FIG. 6, when the connection portion (here, the side lead portion 278) does not have gas permeability, since there is no portion "covered by the connection portion having gas permeability" in the outer periphery of the lead-out portion 277e, the first outer peripheral length L1 is 0 mm. Therefore, the second outer peripheral length L2 of the portion exposed outside the sensor element 101 described above in the outer periphery of the lead-out portion 277e is equal to the outer peripheral length L. Also in this case, regarding this outer peripheral length L (= second outer peripheral length L2), it may be configured in the same manner as the sensor element 101, for example, so as to be less than 1.30 mm.

[0095] Note that the above-mentioned area S is the area of the portion of the lead-out portion (e.g., lead-out portion 77e and lead-out portion 277e) covered by the connection portion regardless of whether the connection portion (e.g., side surface lead portion 78 and side surface lead portion 278) has gas permeability. Therefore, in the sensor element 201 of FIG. 6, regardless of whether the side surface lead portion 278 has gas permeability, the area of the portion of the lead-out portion 277e covered by the side surface lead portion 278 is equal to the area S. Regarding this area S, for example, 0.0011 mm 2 It may be configured in the same manner as the sensor element 101, such as being configured so as to be the above.

[0096] In the above-described embodiment, the connector electrode 75a is connected to the measurement electrode 44 via the inner lead portion 77 and the side lead portion 78, but it is not limited thereto. For example, as shown in the sensor element 401 of the modification of FIG. 7, the element body 102 may be replaced with the element body 402, the inner lead portion 77 and the side lead portion 78 may be replaced with the inner lead portion 477 and the through-hole conductor 478, and the connector electrode 75a may be replaced with the connector electrode 475a. The element body 402 of the sensor element 401 has a through-hole 402h. The through-hole 402h includes an opening that opens on the first surface 102a of the element body 402 and penetrates the spacer layer 5 and the second solid electrolyte layer 6 in the stacking direction (vertical direction). The inner lead portion 477 is disposed inside the element body 402, specifically, between the first solid electrolyte layer 4 and the spacer layer 5, similar to the inner lead portion 77 of the sensor element 101. Note that at least a part of the inner lead portion 477 is surrounded by a lead insulating layer (not shown) on its outer periphery, similar to the inner lead portion 77. The through-hole conductor 478 is disposed in the through-hole 402h via an insulating layer 479, and the lower end is connected to the inner lead portion 477. The lead-out portion 478e, which is the upper end of the through-hole conductor 478, is the exit portion to the opening of the through-hole 402h on the first surface 102a. The lead-out portion 478e is covered with the connector electrode 475a and connected thereto so that the whole thereof is not exposed to the outside of the sensor element 401. The shape of the lead-out portion 478e is, for example, circular in a top view. The connector electrode 475a has gas permeability. In this case, the inner lead portion 477 and the through-hole conductor 478 correspond to the inner conduction portion of the present invention, the lead-out portion 478e corresponds to the lead-out portion of the present invention, and the connector electrode 75a corresponds to the outer conduction portion and the connection portion of the present invention. In this sensor element 401, the connector electrode 475a has gas permeability, and the outer periphery of the lead-out portion 478e has no portion exposed to the outside of the sensor element 401. Therefore, the outer peripheral length of the entire outer periphery of the lead-out portion 478e covered with the connector electrode 475a, for example, if the lead-out portion 478e is circular in a top view, the outer peripheral length of the circle is the outer peripheral length L (= the first outer peripheral length L1). Therefore, with respect to this outer peripheral length L, for example, it may be configured to be less than 1.30 mm, similar to the sensor element 101.Also, the area of the entire lead-out portion 478e covered by the connector electrode 475a is the area S. Therefore, for this area S, for example, it is 0.0011 mm². 2 It may be configured in the same manner as the sensor element 101, such as being configured so as to be as described above.

[0097] In the sensor element 401, although the lead-out portion 478e, which is the upper end of the through-hole conductor 478, is assumed to be entirely covered by the connector electrode 75, it is not limited to this. For example, as shown in the sensor element 501 of the modification in FIG. 8, the connector electrode 75a may be replaced with the connector electrode 575a, and the through-hole conductor 478 may be replaced with the through-hole conductor 578. Similar to the through-hole conductor 478, the through-hole conductor 578 is disposed in the through-hole 402h via the insulating layer 579, and the lower end is connected to the inner lead portion 477. The lead-out portion 578e, which is the upper end of the through-hole conductor 478, is the exit portion to the opening of the through-hole 402h on the first surface 102a. The shape of the lead-out portion 578e is, for example, circular in a top view. The connector electrode 575a has a circular hole 575h, and the outer peripheral portion of the hole 575h on the lower end surface of the connector electrode 575a is connected to the outer peripheral portion of the lead-out portion 578e of the through-hole conductor 578. Therefore, the portion of the lead-out portion 578e of the through-hole conductor 578 excluding the outer peripheral portion is exposed to the outside of the sensor element 501. The connector electrode 575a has gas permeability. In this case, the inner lead portion 477 and the through-hole conductor 578 correspond to the inner conduction portion of the present invention, the lead-out portion 578e corresponds to the lead-out portion of the present invention, and the connector electrode 575a corresponds to the outer conduction portion and the connection portion of the present invention. Similar to the sensor element 401, this sensor element 501 also has the connector electrode 575a having gas permeability, and the outer periphery of the lead-out portion 578e does not have a portion exposed to the outside of the sensor element 501. Therefore, the outer peripheral length of the entire outer periphery of the lead-out portion 578e covered by the connector electrode 575a, for example, if the lead-out portion 578e is circular in a top view, the outer peripheral length of the circle becomes the outer peripheral length L (= the first outer peripheral length L1). Therefore, for this outer peripheral length L, it may be configured in the same manner as the sensor element 101, for example, so as to be less than 1.30 mm. Also, the area of the portion of the lead-out portion 478e covered by the connector electrode 575a, that is, the area of the upper surface of the lead-out portion 478e excluding the portion exposed to the hole 575h, becomes the area S. Therefore, for this area S, it may be configured in the same manner as the sensor element 101, for example, so as to be 0.0011 mm 2 It may be configured in the same manner as the sensor element 101, for example, so as to be as described above.

[0098] In the above-described embodiment, the conduction part 74 corresponding to the measurement electrode 44 has been described. However, the conduction part 74 corresponding to any of the inner pump electrode 22, the auxiliary pump electrode 51, and the reference electrode 42 may be configured in the same manner. For example, just as the conduction part 74 corresponding to the measurement electrode 44 includes the connector electrode 75a and the lead part 76 having the inner lead part 77 and the side lead part 78, when the conduction part 74 corresponding to the inner pump electrode 22 includes the connector electrode 75h and the lead part having the inner lead part and the side lead part, the leading-out part and the side lead part of this inner lead part may be configured in the same manner as the leading-out part 77e and the side lead part 78 of the sensor element 101, for example, such that the outer peripheral length L is less than 1.30 mm.

[0099] In the above-described embodiment, the oxygen concentration adjustment chamber had the first internal cavity 20 and the second internal cavity 40, but it is not limited thereto. For example, the oxygen concentration adjustment chamber may further include another internal cavity, or one of the first internal cavity 20 and the second internal cavity 40 may be omitted. Similarly, in the above-described embodiment, the adjustment pump cell had the main pump cell 21 and the auxiliary pump cell 50, but it is not limited thereto. For example, the adjustment pump cell may further include another pump cell, or one of the main pump cell 21 and the auxiliary pump cell 50 may be omitted. For example, when the oxygen concentration of the gas to be measured can be sufficiently lowered by the main pump cell 21 alone, the auxiliary pump cell 50 may be omitted. When the auxiliary pump cell 50 is omitted, the control unit 96 may perform only the main pump control process as the adjustment pump control process. Also, in the main pump control process, the setting of the target value V0* based on the pump current Ip1 described above may be omitted. Specifically, a predetermined target value V0* may be stored in the storage unit 98 in advance, and the control unit 96 may control the main pump cell 21 by feedback-controlling the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value V0*.

[0100] In the above-described embodiments, the sensor element 101 of the gas sensor 100 is provided with the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61, but it is not limited thereto. For example, as shown in the sensor element 601 of the modification of FIG. 10, it may not be provided with the third internal cavity 61. In the sensor element 601 of the modification of FIG. 10, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, there are a gas inlet 10, a first diffusion rate-limiting portion 11, a buffer space 12, a second diffusion rate-limiting portion 13, a first internal cavity 20, a third diffusion rate-limiting portion 30, and a second internal cavity 40, which are adjacent and communicated in this order. Further, the measurement electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 within the second internal cavity 40. The measurement electrode 44 is covered by a fourth diffusion rate-limiting portion 45. The fourth diffusion rate-limiting portion 45 is a film formed of a ceramic porous body such as alumina (Al 2 O 3 ). The fourth diffusion rate-limiting portion 45, similar to the fourth diffusion rate-limiting portion 60 of the above-described embodiments, plays a role of limiting the amount of NOx flowing into the measurement electrode 44. Further, the fourth diffusion rate-limiting portion 45 also functions as a protective film for the measurement electrode 44. The ceiling electrode portion 51a of the auxiliary pump electrode 51 is formed up to directly above the measurement electrode 44. Even with the sensor element 601 having such a configuration, similar to the above-described embodiments, the NOx concentration can be detected by the measurement pump cell 41. In the sensor element 601 of FIG. 10, the periphery of the measurement electrode 44 functions as a measurement chamber. That is, the periphery of the measurement electrode 44 plays the same role as the third internal cavity 61.

[0101] In the above-described embodiments, the outer pump electrode 23 serves as an electrode paired with the inner pump electrode 22 in the main pump cell 21 (also referred to as an outer main pump electrode), an electrode paired with the auxiliary pump electrode 51 of the auxiliary pump cell 50 (also referred to as an outer auxiliary pump electrode), and an electrode paired with the measurement electrode 44 of the measurement pump cell 41 (also referred to as an outer measurement electrode), but it is not limited thereto. Any one or more of the outer main pump electrode, the outer auxiliary pump electrode, and the outer measurement electrode may be provided outside the element body 102 in contact with the gas to be measured separately from the outer pump electrode 23.

[0102] In the above-described embodiment, the sensor element 101 is configured to detect the NOx concentration in the gas to be measured. However, the present invention is not limited thereto as long as it can detect the concentration of a specific gas in the gas to be measured. For example, the concentration of an oxide other than NOx may be used as the specific gas concentration. When the specific gas is an oxide, oxygen is generated when the specific gas itself is reduced in the third internal cavity 61 as in the above-described embodiment. Therefore, the measurement pump cell 41 can detect the specific gas concentration by obtaining a detection value (for example, pump current Ip2) corresponding to this oxygen. Further, the specific gas may be a non-oxide such as ammonia. When the specific gas is a non-oxide, oxygen is generated when the gas after conversion is reduced in the third internal cavity 61 by converting the specific gas into an oxide (for example, converting ammonia into NO). Therefore, the measurement pump cell 41 can detect the specific gas concentration by obtaining a detection value (for example, pump current Ip2) corresponding to this oxygen. For example, the inner pump electrode 22 in the first internal cavity 20 can function as a catalyst to convert ammonia into NO in the first internal cavity 20.

[0103] In the above-described embodiment, the element body 102 of the sensor element 101 is a laminate having a plurality of solid electrolyte layers (layers 1 to 6). However, the present invention is not limited thereto. The element body 102 only needs to include at least one oxygen ion-conductive solid electrolyte layer. For example, in FIG. 2, layers 1 to 5 other than the second solid electrolyte layer 6 may be layers made of a material other than the solid electrolyte layer (for example, a layer made of alumina). In this case, each electrode included in the sensor element 101 may be disposed on the second solid electrolyte layer 6. For example, the measurement electrode 44 in FIG. 2 may be disposed on the lower surface of the second solid electrolyte layer 6. Further, instead of providing the reference gas introduction space 43 in the first solid electrolyte layer 4, it may be provided in the spacer layer 5, and instead of providing the reference gas introduction layer 48 between the first solid electrolyte layer 4 and the third substrate layer 3, it may be provided between the second solid electrolyte layer 6 and the spacer layer 5. The reference electrode 42 may be provided behind the third internal cavity 61 and on the lower surface of the second solid electrolyte layer 6.

[0104] In the above-described embodiment, the control unit 96 sets the target value V0* of the voltage V0 based on the pump current Ip1 (feedback control) so that the pump current Ip1 becomes the target value Ip1*, and feedback-controls the pump voltage Vp0 so that the voltage V0 becomes the target value V0*. However, other control may be performed. For example, the control unit 96 may feedback-control the pump voltage Vp0 based on the pump current Ip1 so that the pump current Ip1 becomes the target value Ip1*. That is, the control unit 96 may omit the acquisition of the voltage V0 from the oxygen partial pressure detection sensor cell 80 for main pump control and the setting of the target value V0*, and directly control the pump voltage Vp0 (and thus control the pump current Ip0) based on the pump current Ip1.

[0105] In the above-described embodiment, the form of the gas sensor 100 including the sensor elements 101, 201, etc. has been described. However, it goes without saying that the form of the sensor elements 101, 201, etc. used in the gas sensor 100 may also be such.

Example

[0106] Hereinafter, an example in which the sensor element is specifically manufactured will be described as an example. Note that the present invention is not limited to the following examples.

[0107] [Examples 1 to 6 and Comparative Examples 1 and 2] By the above-described manufacturing method, the sensor element 101 shown in FIG. 2 or the gas sensor 100 shown in FIG. 1 was fabricated, and Examples 1 to 6 and Comparative Examples 1 and 2 were obtained. In fabricating the sensor element 101, the ceramic green sheet was formed by tape casting after mixing zirconia particles added with 4 mol% of yttria as a stabilizer, an organic binder, and an organic solvent. For the paste for forming the pattern of the side lead portion 78, a paste containing a noble metal and alumina was used. For the paste for forming the pattern of the inner lead portion 77, a paste containing a noble metal and zirconia was used. In Examples 1 to 6 and Comparative Examples 1 and 2, the outer peripheral length L (= first outer peripheral length L1) and the area S of the lead-out portion 77e were variously changed as shown in Table 1. The change in the outer peripheral length L and the area S was performed by adjusting the width in the front-rear direction of the pattern of the portion that becomes the lead-out portion 77e in the inner lead portion 77 or by adjusting the thickness of the lead-out portion 77e as described above. Further, the gas sensor 100 shown in FIG. 1 was fabricated by the above-described manufacturing method using a rubber stopper 157 that was processed so that no volatile organic gas was generated in Evaluation Test 1 described later, and used as a reference gas sensor. Note that the sensor element 101 of the reference gas sensor was the same as the sensor element of Example 1.

[0108]

Table 1

[0109] [Evaluation Test 1] For each of the reference gas sensor and the gas sensors 100 of Examples 1 to 6 and Comparative Examples 1 and 2, an evaluation test of the detection accuracy of the pump current Ip2 was conducted. First, each of the reference gas sensor and the gas sensors 100 of Examples 1 to 6 and Comparative Examples 1 and 2 was attached to a pipe such that the tip-side portion of the element body 102 of the sensor element 101 protruded into the pipe, and a temperature sensor was attached to the rubber stopper 157. Subsequently, the heater control process was started to raise the heater 71a to 800°C. Then, a gas obtained by burning a mixture of liquefied petroleum gas (LPG) and air with a burner was flowed through the pipe as the gas to be measured. At this time, the flow rates of LPG and air were adjusted such that the air-fuel ratio λ = 1.05 and the temperature of the gas to be measured was 740°C. The inventor had previously confirmed by another experiment and analysis that the NOx concentration of the gas to be measured was approximately 100 ppm in this case. While flowing the gas to be measured through the pipe in this way, the adjustment pump control process and the measurement pump control process were executed, and the pump current Ip2 was detected over 2 hours. The value obtained by converting the pump current Ip2 of the reference gas sensor into NOx concentration [ppm] was used as the reference value, and the values obtained by converting the pump currents Ip2 of the gas sensors 100 of Examples 1 to 6 and Comparative Examples 1 and 2 into NOx concentration [ppm] were used as the evaluation target values. For each of the gas sensors 100 of Examples 1 to 6 and Comparative Examples 1 and 2, the concentration deviation obtained by subtracting the evaluation target value from the reference value at each time was calculated. When the maximum value of the concentration deviation was 7 ppm or less, it was evaluated as very good (A). When the maximum value of the difference exceeded 7 ppm and was less than 15 ppm, it was evaluated as good (B). When the maximum value of the difference was 15 ppm or more, it was evaluated as poor (F).

[0110] [Evaluation Test 2] For each of the gas sensors 100 of Examples 1 to 6 and Comparative Example 1, a durability test was conducted at a high current density to evaluate the peel resistance of the side lead portion 78 from the third surface 102c of the element body 102. First, the durability test was conducted as follows. Each of the reference gas sensor, the gas sensors 100 of Examples 1 to 6, and Comparative Examples 1 and 2 was attached to a pipe such that the tip side portion of the element body 102 of the sensor element 101 protruded into the pipe. A model gas with a base gas of nitrogen, an oxygen concentration of 0%, a NOx concentration of 3000 ppm, and a pressure of 1 atm was prepared and flowed through the pipe as the gas to be measured. In parallel with this, heater control processing was started. When the heater 71a reached 800 °C, adjustment pump control processing and measurement pump control processing were started, and the pump current Ip2 was detected over 150 seconds. In this durability test, since the NOx concentration of the model gas is as high as 3000 ppm, the pump current Ip2 becomes a relatively large value, so a state is maintained in which the current density of the current flowing through the side lead portion 78 and the lead-out portion 77e of the inner lead portion 77 tends to be high. Then, by examining the presence or absence of an abnormality in the detected value of the pump current Ip2 during the durability test (for example, the value becoming 0 μA), the presence or absence of an electrical conduction abnormality between the side lead portion 78 and the lead-out portion 77e was examined. For the gas sensor 100 in which no conduction abnormality occurred during the durability test, the presence or absence of peeling between the side lead portion 78 and the third surface 102c of the element body 102 was examined. FIGS. 10 and 11 are explanatory diagrams for explaining the method of investigating the presence or absence of peeling between the side lead portion 78 and the third surface 102c of the element body 102. First, the sensor element 101 was cut along the thick broken line in FIG. 10. The thick broken line in FIG. 10 passes through the central portion in the front-rear direction of the side lead portion 78 and is a line for dividing the sensor element 101 into a front end side and a rear end side. FIG. 11 corresponds to the cut surface on the rear end side of the sensor element 101. Subsequently, the sensor element 101 was observed at a magnification of 500 times using SEM at the five thick solid line frames in FIG. 11 and observed at a magnification of 3000 times using SEM at the five thick broken line frames in FIG. 11. The five thick solid line frames and the five thick broken line frames were defined to include the boundary between the side lead portion 78 and the third surface 102c of the element body 102.When a portion where the distance between the side lead portion 78 and the third surface 102c of the element body 102 is 0.020 mm or more is recognized at at least one of the 10 locations, it is regarded as having peeling, and when no portion where this distance is 0.020 mm or more is recognized, it is regarded as having no peeling. For each of the gas sensors 100 of Examples 1 to 6 and Comparative Example 1, when there was an abnormality in conduction during the durability test, it was evaluated as unacceptable (F), and when there was no abnormality in conduction but there was peeling between the side lead portion 78 and the third surface 102c of the element body 102, it was evaluated as good (B), and when there was no peeling between the side lead portion 78 and the third surface 102c of the element body 102, it was evaluated as very good (A).

[0111] As can be seen from Table 1, as a result of Evaluation Test 1, among Examples 1 to 6 and Comparative Examples 1 and 2, Comparative Example 2 in which the outer peripheral length L of the lead-out portion 77e was 1.30 mm or more was evaluated as unacceptable (F), while Examples 1 to 6 and Comparative Example 1 in which the outer peripheral length L was less than 1.30 mm were all evaluated as very good (A) or good (B). Therefore, when the outer peripheral length L is less than 1.30 mm, it is possible to suppress a decrease in the pump current Ip2 due to the volatile organic gas generated from the rubber stopper 157 and suppress a decrease in the detection accuracy of the concentration of the specific gas (NOx). And among Examples 1 to 6 and Comparative Example 1, Example 6 in which the outer peripheral length L of the lead-out portion 77e exceeded 1.15 mm was evaluated as good (B), while Examples 1 to 5 and Comparative Example 1 in which the outer peripheral length L was 1.15 mm or less were evaluated as very good (A). Therefore, when the outer peripheral length L is 1.15 mm or less, it is possible to further suppress a decrease in the detection accuracy of the concentration of the specific gas (NOx).

[0112] As a result of Evaluation Test 2, among Examples 1 to 6 and Comparative Example 1, Comparative Example 1 in which the area S of the lead-out portion 77e was less than 0.0011 mm 2 was evaluated as unacceptable (F), while Examples 1 to 6 in which the area S was 0.0011 mm 2 or more were all evaluated as very good (A) or good (B). Therefore, when the area S is 0.0011 mm 2By being as described above, it is possible to suppress the heat generation of the lead-out portion 77e and / or the side lead portion 78 due to the current flowing through the side lead portion 78 and the lead-out portion 77e, and suppress the degree of peeling of the side lead portion 78 due to thermal expansion. Among Examples 1 to 6, Example 1 in which the area S is less than 0.0012 mm 2 was evaluated as good (B), while Examples 2 to 6 in which the area S is 0.0012 mm 2 or more were evaluated as very good (A). Therefore, by the area S being 0.0012 mm 2 or more, it is possible to further suppress the degree of peeling of the side lead portion 78 due to thermal expansion. Note that since Comparative Example 2 was evaluated as unacceptable (F) in Evaluation Test 1, Evaluation Test 2 was omitted.

Industrial Applicability

[0113] The present invention can be used for a sensor element for detecting the concentration of a specific gas such as NOx in a gas to be measured such as the exhaust gas of an internal combustion engine, and a gas sensor including the same.

Explanation of Signs

[0114] 1 First substrate layer, 2 Second substrate layer, 3 Third substrate layer, 4 First solid electrolyte layer, 5 Spacer layer, 6 Second solid electrolyte layer, 7 Adhesive layer, 10 Gas inlet, 11 First diffusion rate-limiting part, 12 Buffer space, 13 Second diffusion rate-limiting part, 20 First internal cavity, 21 Main pump cell, 22 Inner pump electrode, 22a, 51a Ceiling electrode part, 22b, 51b Bottom electrode part, 23 Outer pump electrode, 24 Variable power source, 30 Third diffusion rate-limiting part, 40 Second internal cavity, 41 Measurement pump cell, 42 Reference electrode, 43 Reference gas introduction space, 44 Measurement electrode, 45 Fourth diffusion rate-limiting part, 46 Variable power source, 48 Reference gas introduction layer, 49 Reference gas introduction part, 49a Inlet part, 50 Auxiliary pump cell, 51 Auxiliary pump electrode, 52 Variable power source, 60 Fourth diffusion rate-limiting part, 61 Third internal cavity, 70 Heater part, 71a Heater, 71b Heater insulation layer, 71c Pressure dissipation hole, 72 Heater power source, 74 Conductive part, 75, 75a~75h, 475a, 575a Connector electrode, 76 Lead part, 77, 277, 477 Inner lead part, 77a~77d First to fourth parts, 77e, 277e, 478e, 578e Lead-out part, 78, 278 Side lead part, 79 Lead insulation layer, 80 Oxygen partial pressure detection sensor cell for main pump control, 81 Oxygen partial pressure detection sensor cell for auxiliary pump control, 82 Oxygen partial pressure detection sensor cell for measurement pump control, 83 Sensor cell, 95 Control device, 96 Control part, 97 CPU, 98 Memory part, 100 Gas sensor, 101, 201, 401, 501, 601 Sensor element, 102, 402 Element body, 102a First surface, 102b Second surface, 102c Third surface, 102d Fourth surface, 102e Fifth surface, 102f Sixth surface, 130 Protection cover, 131 Inner protection cover, 132 Outer protection cover, 133 Sensor element chamber, 140 Sensor assembly, 141 Element sealing body, 142 Main body fitting, 143 Inner cylinder, 143a, 143b Reduced diameter part, 144a~144c Ceramic supporter, 145a, 145b Compressed powder body, 146 Metal ring, 147 Bolt, 148 Outer cylinder, 149 Space, 150 Connector, 155 Lead wire, 157 Rubber stopper, 190 Pipe, 191 Fixing member, 402h Through hole, 478, 578 Through hole conductor, 479 Insulation layer, 575h Hole.

Claims

1. A sensor element for detecting the concentration of a specific gas in a gas to be measured, comprising: a columnar element body having an oxygen ion conductive solid electrolyte layer and extending along a longitudinal direction, the element body having a front end and a rear end which are both ends along the longitudinal direction and a side surface which is a surface along the longitudinal direction, and the front end side being exposed to the gas to be measured; an inner electrode disposed inside the element body; a conduction part having an inner conduction part disposed inside the element body and conducting with the inner electrode, an outer conduction part having a connector electrode disposed on the side surface and on the rear end side of the side surface and conducting with the inner conduction part; wherein: the inner conduction part has a lead-out part which is an outlet part from the inside of the element body to the side surface; the outer conduction part has a connection part connected to the lead-out part of the inner conduction part; the connection part of the outer conduction part has gas permeability, and / or at least a part of the lead-out part of the inner conduction part is exposed to the outside of the sensor element; for the outer periphery of the lead-out part of the inner conduction part, the outer periphery length which is the sum of the first outer periphery length of the part covered by the connection part having gas permeability and the second outer periphery length of the part exposed to the outside of the sensor element is less than 1.30 mm; a sensor element.

2. The sensor element according to Claim 1, wherein: the outer periphery length is 1.15 mm or less. a sensor element.

3. The sensor element according to Claim 1 or 2, Among the lead-out portions of the inner conduction portion, the area of the portion covered by the connection portion of the outer conduction portion is 0.0011 mm 2 or more. a sensor element.

4. The sensor element according to Claim 3, The area is 0.0012 mm 2 or more a sensor element.

5. The sensor element according to Claim 1 or 2, wherein: the inner electrode is a measurement electrode used for detecting the concentration of the specific gas. a sensor element.

6. The sensor element according to Claim 1 or 2, wherein: the element body is a laminate in which a plurality of layers including the solid electrolyte layer are laminated in a lamination direction orthogonal to the longitudinal direction; the laminate has, as the side surface, a first surface and a second surface which are both end surfaces in the lamination direction, and a third surface and a fourth surface which are both end surfaces in a direction orthogonal to the longitudinal direction and the lamination direction; the inner conduction part has an inner lead part having the lead-out part which is an outlet part to the third surface or the fourth surface; the connection part is a side lead part disposed on the third surface or the fourth surface and connected to the lead-out part. a sensor element.

7. The sensor element according to Claim 1 or 2, wherein: The element body is a laminate in which a plurality of layers including the solid electrolyte layer are laminated in a stacking direction orthogonal to the longitudinal direction. The laminate has, as the side surfaces, a first surface and a second surface which are both end surfaces in the stacking direction. The element body includes an opening that opens on the first surface or the second surface on the rear end side of the side surface, and has a through hole that penetrates one or more of the plurality of layers in the stacking direction. The inner conduction part has a through hole conductor disposed in the through hole and having a lead-out part that serves as an outlet part to the opening. The connection part is the connector electrode and is connected to the lead-out part of the through hole conductor. Sensor element.

8. The sensor element according to claim 1 or 2, The sensor element, A case that is cylindrical and extends along the longitudinal direction of the sensor element, has a second front end and a second rear end that are both ends along the longitudinal direction, and in which the sensor element is disposed inside, A sealing member that seals the second rear end side of the case, Used for a gas sensor comprising, Sensor element.

9. The sensor element according to claim 1 or 2, A case that is cylindrical and extends along the longitudinal direction of the sensor element, has a second front end and a second rear end that are both ends along the longitudinal direction, and in which the sensor element is disposed inside, A sealing member that seals the second rear end side of the case, A gas sensor comprising.

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