Sensor element and gas sensor

Abstract

To prevent the influence of the dynamic pressure of gas to be measured on a pump cell.SOLUTION: A sensor element is to detect the concentration of specific gas in gas to be measured, and the sensor element comprises: an element body provided therein with a gas-to-be-measured circulation part that introduces the gas to be measured from a gas introduction port and circulates the gas in a fore-and-aft direction; and a diffusion rate determination unit 11a that is provided in the gas-to-be-measured circulation part and applies diffusion resistance to the gas to be measured introduced from the gas introduction port. The diffusion rate determination unit 11a has, in at least part of the fore-and-aft direction, a first porous body 87a that is provided to occupy part of a cross section orthogonal to the fore-and-aft direction and allows the gas to be measured to pass through, and a first space part 85a that includes a portion of the cross section not occupied by the first porous body 87a and allows the gas to be measured to pass through.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Conventionally, gas sensors for detecting the concentration of a specific gas, such as NOx, in a measurement gas, such as exhaust gas from an internal combustion engine, have been known. For example, Patent Document 1 (Patent Document 1) describes a gas sensor including a sensor element having an element body, a main pump cell, an auxiliary pump cell, and a measurement pump cell. The element body has a measurement gas flow section therein, which includes an oxygen-ion-conductive solid electrolyte layer and through which the measurement gas is introduced and circulated. The main pump cell has an inner main pump electrode disposed in a first internal space of the measurement gas flow section and an outer main pump electrode disposed in a portion of the element body exposed to the measurement gas outside. The auxiliary pump cell has an inner auxiliary pump electrode disposed in a second internal space of the measurement gas flow section downstream of the first internal space and an outer auxiliary pump electrode disposed in a portion of the element body exposed to the measurement gas outside. The measurement pump cell has an inner measurement electrode disposed in a measurement chamber downstream of the second internal space in the measurement gas flow section, and an outer measurement electrode disposed in a portion of the element body exposed to the measurement gas on the outside. When using this sensor element to detect the NOx concentration, the oxygen concentration of the measurement gas is first adjusted in the first and second internal spaces by the main pump cell and auxiliary pump cell. Then, the NOx in the measurement gas after the oxygen concentration adjustment is reduced in the measurement chamber. The NOx concentration in the measurement gas is detected based on the pump current that flows when the measurement pump cell pumps out the oxygen generated by the reduction of NOx. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-181499 Summary of the Invention [Problem to be solved by the invention]

[0004] In such gas sensors, even if the composition of the measured gas is the same, different values ​​of the dynamic pressure of the measured gas may cause the operation of the pump cell of the gas sensor (for example, the value of the pump current flowing through the pump cell of the sensor element) to differ. As a result, the dynamic pressure of the measured gas may affect the detection accuracy of the concentration of a specific gas. Therefore, it is desirable to suppress the effect of the dynamic pressure of the measured gas on the pump cell.

[0005] The present invention has been made to solve the above problems, and its main object is to suppress the influence of the dynamic pressure of the gas to be measured on the pump cell. [Means for solving the problem]

[0006] In order to achieve the above-mentioned main object, the present invention employs the following means.

[0007] [1] The sensor element of the present invention is A sensor element for detecting the concentration of a specific gas in a measurement gas, an element body having an oxygen ion conductive solid electrolyte layer and a measurement gas flow section provided therein for introducing the measurement gas from a gas inlet and flowing the measurement gas in a first direction; a pump cell having an inner electrode provided in an internal space of the measurement gas flow portion and an outer electrode provided on an outer surface of the element body; a diffusion rate-controlling section provided in the measurement gas flow section upstream of the internal space and configured to provide a diffusion resistance to the measurement gas introduced through the gas inlet; Equipped with the diffusion-controlling portion includes a porous body that is provided in at least a part of the first direction so as to occupy a part of a cross section perpendicular to the first direction and through which the measurement gas can pass; and a space portion that includes a part of the cross section that is not occupied by the porous body and through which the measurement gas can pass. It is something.

[0008] This sensor element has a diffusion-controlling section, which is a part of a measurement gas flow section that allows the measurement gas to flow in a first direction, and the diffusion-controlling section has a porous body that occupies a part of a cross section perpendicular to the first direction in at least a part of the first direction, and a space section that includes a part of the cross section that is not occupied by the porous body. This makes it possible to make the flow rates of the measurement gas passing through the porous body and the measurement gas passing through the space section different in the cross section perpendicular to the first direction of the diffusion-controlling section, thereby generating turbulence in the measurement gas after passing through and increasing the pressure loss of the measurement gas. This therefore makes it possible to suppress the effect of the dynamic pressure of the measurement gas on a pump cell having an inner electrode provided downstream of the diffusion-controlling section.

[0009] [2] In the sensor element described above (the sensor element described in [1] above), the porous body may be disposed in the diffusion-controlling portion so as to occupy 30% to 70% of the cross section.

[0010] [3] In the sensor element described in [1] or [2] above, the porosity of the porous body may be 15% or less. This allows the difference in flow rate between the measurement gas passing through the porous body and the measurement gas passing through the space to be greater, thereby increasing the pressure loss of the measurement gas after passing through.

[0011] [4] In the sensor element described above (the sensor element according to any one of [1] to [3] above), the porous body may be provided in plurality so as to form parallel flow paths in the cross section.

[0012] [5] In the sensor element described in any one of [1] to [4] above, the element body has a longitudinal direction and is a laminate formed by stacking multiple layers, including the solid electrolyte layer, in a stacking direction perpendicular to the longitudinal direction. The cross-sectional shape of the space portion is a predetermined shape having a longer periphery than a reference rectangle. The reference rectangle has the same area as the cross-section of the space portion and may be a circumscribed rectangle of the cross-section, which is formed by two sides parallel to the stacking direction and two sides parallel to a second direction perpendicular to the stacking direction, and may be a rectangle obtained by shortening the short sides while maintaining the long side lengths, a rectangle obtained by deforming the reference rectangle while maintaining the ratio of the sides, or a rectangle obtained by changing the lengths of the sides to maximize the overlapping area with the cross-section. In this way, the hydraulic diameter of the space portion of the diffusion-controlling section, which has a cross-sectional shape perpendicular to the first direction, becomes smaller than the reference rectangle, thereby increasing the pressure loss of the measurement gas passing through the space portion. Therefore, the pump cell having the inner electrode provided downstream of the diffusion-controlling section can be prevented from being affected by the dynamic pressure of the measured gas. Therefore, this shape also makes it possible to prevent the pump cell having the inner electrode provided downstream of the diffusion-controlling section from being affected by the dynamic pressure of the measured gas.

[0013] [6] In the above-mentioned sensor element (the sensor element described in [5]), the outer periphery of the predetermined shape has a first part and a second part that face each other in the stacking direction and extend along the second direction, and at least a part of the first part and / or at least a part of the second part may be curved.

[0014] [7] In the above-mentioned sensor element (the sensor element described in [5] or [6]), the outer periphery of the predetermined shape has a first part and a second part that face each other in the stacking direction and extend along the second direction, and at least a part of the first part and / or at least a part of the second part may be in the shape of a broken line.

[0015] [8] In the sensor element described above (the sensor element described in [6] or [7] above), the first portion and the second portion may have a convex shape on the same side in the stacking direction.

[0016] [9] In the sensor element described above (the sensor element described in [6] or [7]), the first portion and the second portion may have a convex shape on the side approaching each other or on the side moving away from each other in the stacking direction.

[0017]

[10] In the sensor element described above (the sensor element described in any one of [5] to [9]), the diffusion-controlling portion may have a plurality of the space portions, and each of the plurality of space portions may have the cross-sectional shape of the predetermined shape.

[0018]

[11] In the sensor element described above (the sensor element described in any one of [1] to

[10] above), the diffusion-controlling portion may be formed so that at least a part of the diffusion-controlling portion downstream of the upstream end has a smaller cross-sectional area perpendicular to the first direction than the upstream end. This increases the pressure loss of the measurement gas passing through the portion of the space having a smaller cross-sectional area than the upstream end. Therefore, this shape also makes it possible to suppress the influence of the dynamic pressure of the measurement gas on the pump cell having the inner electrode provided downstream of the diffusion-controlling portion.

[0019]

[12] In the sensor element described above (the sensor element described in

[11] above), the diffusion-controlling portion may extend such that a cross-sectional contour parallel to the first direction is curved with respect to the first direction.

[0020]

[13] A gas sensor according to the present invention includes the sensor element according to any one of the above items [1] to

[12] . Therefore, this gas sensor can achieve the same effects as the above-described sensor element, such as suppressing the influence of the dynamic pressure of the gas to be measured on the pump cell. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of the configuration of a gas sensor 100. FIG. [Figure 2] View A of Figure 1. [Figure 3] Cross section B-B of Figure 1. [Figure 4] FIG. 3 is a block diagram showing the electrical connection relationship between the control device 95 and each cell, etc. [Figure 5] Cross section CC of Figure 3. [Figure 6] 4A to 4C are partial cross-sectional views showing the steps of manufacturing the diffusion rate-controlling portion 11a. [Figure 7] FIG. 10 is an explanatory diagram of a first diffusion rate-controlling part 11 of a modified example. [Figure 8] FIG. 10 is an explanatory diagram of a first diffusion rate-controlling part 11a of a modified example. [Figure 9] FIG. 10 is an explanatory diagram of a reference rectangle S1. [Figure 10] FIG. 10 is an explanatory diagram of a reference rectangle S2. [Figure 11] 9 is a partial cross-sectional view showing a manufacturing process of the diffusion rate-controlling portion 11a of FIG. 8. [Figure 12] FIG. 11 is an explanatory diagram of a diffusion rate-controlling part 11a of a modified example. [Figure 13] FIG. 11 is an explanatory diagram of a diffusion rate-controlling part 11a of a modified example. [Figure 14] FIG. 11 is an explanatory diagram of a diffusion rate-controlling part 11a of a modified example. [Figure 15] FIG. 11 is an explanatory diagram of a diffusion rate-controlling part 11a of a modified example. [Figure 16] FIG. 11 is an explanatory diagram of a diffusion rate-controlling part 11a of a modified example. [Figure 17] FIG. 11 is an explanatory diagram of a diffusion rate-controlling part 11a of a modified example. [Figure 18] FIG. 11 is an explanatory diagram of a diffusion rate-controlling part 11a of a modified example. [Figure 19] FIG. 11 is an explanatory diagram of a diffusion rate-controlling part 11a of a modified example. [Figure 20] FIG. 11 is an explanatory diagram of a diffusion rate-controlling part 11a of a modified example. [Figure 21] FIG. 11 is an explanatory diagram of a diffusion rate-controlling part 11a of a modified example. [Figure 22] FIG. 11 is an explanatory diagram of a diffusion rate-controlling part 11a of a modified example. [Figure 23] FIG. 10 is a cross-sectional schematic view showing a first diffusion rate-controlling part 211 of a modified example. [Figure 24] DD cross section of Figure 23. [Figure 25] EE cross section of Figure 24. DETAILED DESCRIPTION OF THE INVENTION

[0022] Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically illustrating an example of the configuration of a gas sensor 100 according to an embodiment of the present invention. FIG. 2 is a view taken along line A in FIG. 1. FIG. 3 is a cross-sectional view taken along line B-B in FIG. 1. FIG. 4 is a block diagram showing the electrical connection between the control device 95 and each cell and the heater 72. FIG. 5 is a cross-sectional view taken along line C-C in FIG. 3, showing the periphery of the first spatial portion 85a of the first diffusion-controlling portion 11. The gas sensor 100 is attached to a pipe such as an exhaust gas pipe of an internal combustion engine. The gas sensor 100 detects the concentration of a specific gas, such as NOx or ammonia, in the measured gas, which is exhaust gas from the internal combustion engine. In this embodiment, the gas sensor 100 measures the NOx concentration as the specific gas concentration. The gas sensor 100 includes a sensor element 101 having an element body 102 in the shape of a long rectangular parallelepiped, cells 21, 41, 50, 80-83 included in the sensor element 101, a heater section 70 provided inside the sensor element 101, and a control device 95 having variable power supplies 24, 46, 52 and a heater power supply 76 and controlling the entire gas sensor 100. In this embodiment, as shown in FIGS. 1 to 3, the longitudinal direction of the element body 102 of the sensor element 101 is defined as the front-to-rear direction (length direction), the stacking direction (thickness direction) of the layers 1 to 6 of the element body 102 is defined as the up-to-down direction, and the direction perpendicular to the front-to-rear direction and the up-to-down direction is defined as the left-to-right direction (width direction). For convenience of illustration, FIG. 5 is shown with the vertical length extended compared to FIG. 2.

[0023] The element body 102 is a laminate formed by stacking six layers, in this order from bottom to top, from the drawing: 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 of which is made of an oxygen-ion conductive solid electrolyte layer such as zirconia (ZrO). The solid electrolyte forming these six layers is dense and airtight. The element body 102 is manufactured, for example, by laminating ceramic green sheets corresponding to each layer after performing predetermined processing and printing a circuit pattern on them, and then firing them to integrate them.

[0024] On the tip end side (left end side in FIG. 1 ) of the sensor element 101 (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, a gas inlet 10, a first diffusion rate-controlling section 11, a buffer space 12, a second diffusion rate-controlling section 13, a first internal space (oxygen concentration adjusting chamber) 20, a third diffusion rate-controlling section 30, a second internal space (oxygen concentration adjusting chamber) 40, a fourth diffusion rate-controlling section 60, and a third internal space (measurement chamber) 61 are formed adjacent to each other and communicate with each other in this order.

[0025] The gas inlet 10, buffer space 12, first internal space 20, second internal space 40, and third internal space 61 are spaces inside the sensor element 101, which are defined by hollowing out the spacer layer 5, with an upper portion defined by the underside of the second solid electrolyte layer 6, a lower portion defined by the upper surface of the first solid electrolyte layer 4, and sides defined by the side surfaces of the spacer layer 5.

[0026] The first diffusion-controlling section 11, the second diffusion-controlling section 13, and the third diffusion-controlling section 30 are each provided as two horizontally elongated slits (with the opening extending in the direction perpendicular to the drawing). FIGS. 2 and 5 show the diffusion-controlling section 11a and the diffusion-controlling section 11b constituting the two slits of the first diffusion-controlling section 11. The fourth diffusion-controlling section 60 is provided as a horizontally elongated slit (with the opening extending in the direction perpendicular to the drawing) formed as a gap with the underside of the second solid electrolyte layer 6. The region from the gas inlet 10 to the third internal space 61 is also referred to as the measurement gas flow section.

[0027] The sensor element 101 (element body 102) includes a reference gas inlet 49 that passes a reference gas from the outside of the sensor element 101 to the reference electrode 42 when measuring the NOx concentration. The reference gas inlet 49 includes a reference gas inlet space 43 and a reference gas inlet layer 48. The reference gas inlet space 43 is a space extending inward from the rear end surface of the sensor element 101. The reference gas inlet space 43 is located between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5, and is defined laterally by the side surface of the first solid electrolyte layer 4. The reference gas inlet space 43 opens at the rear end surface of the sensor element 101, and this opening functions as an inlet 49a of the reference gas inlet 49. The reference gas is introduced into the reference gas inlet space 43 from the inlet 49a. The reference gas inlet 49 applies a predetermined diffusion resistance to the reference gas introduced from the inlet 49a and introduces the reference gas into the reference electrode 42. In this embodiment, the reference gas is air.

[0028] 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. A portion of the upper surface of the reference gas introduction layer 48 is exposed within the reference gas introduction space 43. The reference gas introduction layer 48 is formed 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.

[0029] Reference electrode 42 is an electrode formed in a manner sandwiched between the upper surface of third substrate layer 3 and first solid electrolyte layer 4, and as described above, is surrounded by reference gas introduction layer 48 connected to reference gas introduction space 43. As will be described later, reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) in first internal space 20, second internal space 40, and third internal space 61. Reference electrode 42 is formed as a porous cermet electrode (for example, a cermet electrode of Pt and ZrO2).

[0030] In the measurement gas flow section, the gas inlet 10 is a portion that opens to the external space, and the measurement gas is introduced into the sensor element 101 from the external space through the gas inlet 10. The first diffusion-controlling portion 11 is a portion that imparts a predetermined diffusion resistance to the measurement gas introduced through the gas inlet 10. In this embodiment, the front end of the first diffusion-controlling portion 11 serves as the gas inlet 10. As shown in FIGS. 1 and 2 , the diffusion-controlling portion 11a of the first diffusion-controlling portion 11 is provided between the upper surface of the first bridging portion 5a of the spacer layer 5 and the lower surface of the second solid electrolyte layer 6. The diffusion-controlling portion 11b is provided between the lower surface of the first bridging portion 5a and the upper surface of the first solid electrolyte layer 4. As shown in FIG. 3 , the first bridging portion 5a bridges the front side of the buffer space 12, which is the punched portion of the spacer layer 5, from side to side. The buffer space 12 is a space provided to guide the measurement gas introduced from the first diffusion-controlling section 11 to the second diffusion-controlling section 13. The second diffusion-controlling section 13 is a section that imparts a predetermined diffusion resistance to the measurement gas introduced from the buffer space 12 to the first internal space 20. As shown in FIGS. 1 and 2 , the second diffusion-controlling section 13 is provided between the upper surface of the second bridging section 5b of the spacer layer 5 and the lower surface of the second solid electrolyte layer 6, and between the lower surface of the second bridging section 5b and the upper surface of the first solid electrolyte layer 4. As shown in FIG. 3 , the second bridging section 5b is a section that bridges the buffer space 12, which is a punched portion of the spacer layer 5, and the first internal space 20 from side to side. When the measurement gas is introduced from the outside of the sensor element 101 into the first internal space 20, the measurement gas is suddenly taken into the sensor element 101 through the gas inlet 10 due to pressure fluctuations of the measurement gas in the external space (exhaust pressure pulsations if the measurement gas is automobile exhaust gas). The measurement gas is not introduced directly into the first internal space 20, but is introduced into the first internal space 20 after the pressure fluctuations of the measurement gas are canceled out through the first diffusion-controlling section 11, buffer space 12, and second diffusion-controlling section 13. This makes the pressure fluctuations of the measurement gas introduced into the first internal space 20 almost negligible. The first internal space 20 is provided as a space for adjusting the oxygen partial pressure in the measurement gas introduced through the second diffusion-controlling section 13.The oxygen partial pressure is adjusted by operating the main pump cell 21 .

[0031] The main pump cell 21 is an electrochemical pump cell including an inner pump electrode 22 having a ceiling electrode portion 22a provided on almost the entire lower surface of the second solid electrolyte layer 6 facing the first internal space 20, an outer pump electrode 23 provided on the upper surface of the second solid electrolyte layer 6 in a region corresponding to the ceiling electrode portion 22a so as to be exposed to the outside of the sensor element 101, and the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4 which form a current path between these electrodes.

[0032] 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 define the first internal space 20 and the spacer layer 5 that provides the 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 space 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. Side electrode portions (not shown) are formed on the side wall surfaces (inner surfaces) of the spacer layer 5 that configure both side wall portions of the first internal space 20 so as to connect the ceiling electrode portion 22a and the bottom electrode portion 22b, and are arranged in a tunnel-like structure at the locations where the side electrode portions are provided.

[0033] The inner pump electrode 22 and the outer pump electrode 23 are formed as porous cermet electrodes (for example, a cermet electrode of Pt and ZrO containing 1% Au). The inner pump electrode 22, which comes into contact with the measurement gas, is formed using a material with a weakened ability to reduce the NOx component in the measurement gas.

[0034] In the main pump cell 21, by applying a desired voltage Vp0 between the inner pump electrode 22 and the outer pump electrode 23 and flowing a pump current Ip0 in a positive or negative direction between the inner pump electrode 22 and the outer pump electrode 23, it is possible to pump oxygen from the first internal space 20 out to the external space, or to pump oxygen from the external space into the first internal space 20.

[0035] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere in the first internal space 20, an electrochemical sensor cell, i.e., an oxygen partial pressure detection sensor cell 80 for controlling the main pump, is configured 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.

[0036] The oxygen concentration (oxygen partial pressure) in the first internal space 20 can be determined by measuring the electromotive force (voltage V0) in the main pump control oxygen partial pressure detection sensor cell 80. Furthermore, the pump current Ip0 is controlled by feedback controlling the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes a target value. This allows the oxygen concentration in the first internal space 20 to be maintained at a predetermined constant value.

[0037] The third diffusion-controlling portion 30 is a portion that applies a predetermined diffusion resistance to the measurement gas, the oxygen concentration (oxygen partial pressure) of which has been controlled by the operation of the main pump cell 21 in the first internal space 20, and guides the measurement gas to the second internal space 40. As shown in FIGS. 1 and 2, the third diffusion-controlling portion 30 is provided between the upper surface of the third bridging portion 5c of the spacer layer 5 and the lower surface of the second solid electrolyte layer 6, and between the lower surface of the third bridging portion 5c and the upper surface of the first solid electrolyte layer 4. As shown in FIG. 3, the third bridging portion 5c is a portion that bridges the first internal space 20 and the second internal space 40, which are punched-out portions of the spacer layer 5, from side to side.

[0038] The second internal space 40 is provided as a space for further adjusting the oxygen partial pressure by the auxiliary pump cell 50 for the measurement gas introduced through the third diffusion-controlling section 30 after the oxygen concentration (oxygen partial pressure) has been adjusted in advance in the first internal space 20. This makes it possible to keep the oxygen concentration in the second internal space 40 constant with high precision, thereby enabling the gas sensor 100 to measure the NOx concentration with high precision.

[0039] The auxiliary pump cell 50 is an auxiliary electrochemical pump cell that is configured by an auxiliary pump electrode 51 having a ceiling electrode portion 51a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the second internal space 40, an outer pump electrode 23 (not limited to the outer pump electrode 23, but any appropriate electrode on the outside of the sensor element 101 will suffice), the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4.

[0040] The auxiliary pump electrode 51 is disposed in the second internal space 40 in a tunnel-shaped structure similar to the inner pump electrode 22 disposed in the first internal space 20. That is, a ceiling electrode portion 51a is formed on the lower surface of the second solid electrolyte layer 6, which provides the ceiling surface of the second internal space 40, and a bottom electrode portion 51b is formed on the upper surface of the first solid electrolyte layer 4, which provides the bottom surface of the second internal space 40. Side electrodes (not shown) connecting the ceiling electrode portion 51a and the bottom electrode portion 51b are formed on both wall surfaces of the spacer layer 5, which provide the side walls of the second internal space 40. Like the inner pump electrode 22, the auxiliary pump electrode 51 is also formed using a material with a weakened ability to reduce NOx components in the measurement gas.

[0041] In the auxiliary pump cell 50, by applying a desired voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23, it is possible to pump oxygen in the atmosphere within the second internal space 40 out to the external space or pump oxygen from the external space into the second internal space 40.

[0042] In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal space 40, an electrochemical sensor cell, i.e., an oxygen partial pressure detection sensor cell 81 for controlling the auxiliary pump, is configured 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.

[0043] The auxiliary pump cell 50 performs pumping using a variable power supply 52 whose voltage is controlled based on the electromotive force (voltage V1) detected by the auxiliary pump control oxygen partial pressure detection sensor cell 81. This allows the oxygen partial pressure in the atmosphere within the second internal space 40 to be controlled to a low level that does not substantially affect the measurement of NOx.

[0044] In addition, the pump current Ip1 is used to control the electromotive force of the main pump control oxygen partial pressure detection sensor cell 80. Specifically, the pump current Ip1 is input as a control signal to the main pump control oxygen partial pressure detection sensor cell 80, and the target value of the voltage V0 is controlled to always maintain a constant gradient of the oxygen partial pressure in the measurement gas introduced from the third diffusion-controlling part 30 into the second internal space 40. When used as a NOx sensor, the oxygen concentration in the second internal space 40 is maintained at a constant value of approximately 0.001 ppm by the action of the main pump cell 21 and the auxiliary pump cell 50.

[0045] The fourth diffusion-controlling portion 60 is a portion that applies a predetermined diffusion resistance to the measurement gas, the oxygen concentration (oxygen partial pressure) of which has been controlled by the operation of the auxiliary pump cell 50 in the second internal space 40, and guides the measurement gas to the third internal space 61. The fourth diffusion-controlling portion 60 serves to limit the amount of NOx that flows into the third internal space 61. As shown in FIGS. 1 and 2, the fourth diffusion-controlling portion 60 is provided between the upper surface of the fourth bridging portion 5d of the spacer layer 5 and the lower surface of the second solid electrolyte layer 6, and between the lower surface of the fourth bridging portion 5d and the upper surface of the first solid electrolyte layer 4. As shown in FIG. 3, the fourth bridging portion 5d is a portion that bridges the second internal space 40, which is a punched portion of the spacer layer 5, and the third internal space 61 from side to side.

[0046] The third internal space 61 is provided as a space for performing processing related to measurement of the nitrogen oxide (NOx) concentration in the measurement gas, which is introduced through the fourth diffusion-controlling part 60 after the oxygen concentration (oxygen partial pressure) has been adjusted in advance in the second internal space 40. The NOx concentration is measured mainly in the third internal space 61 by the operation of the measurement pump cell 41.

[0047] The measurement pump cell 41 measures the NOx concentration in the measurement gas in the third internal space 61. The measurement pump cell 41 is an electrochemical pump cell including a measurement electrode 44 provided on the upper surface of the first solid electrolyte layer 4 facing the third internal space 61, the outer pump electrode 23, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4. The measurement electrode 44 is a porous cermet electrode made of a material that has a higher reduction ability for the NOx component in the measurement gas than the inner pump electrode 22. The measurement electrode 44 also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere in the third internal space 61.

[0048] In the measuring pump cell 41, oxygen produced by decomposition of nitrogen oxides in the atmosphere surrounding the measuring electrode 44 is pumped out, and the amount of oxygen produced can be detected as a pump current Ip2.

[0049] Furthermore, in order to detect the oxygen partial pressure around the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, the measurement electrode 44, and the reference electrode 42 constitute an electrochemical sensor cell, i.e., an oxygen partial pressure detection sensor cell 82 for controlling the measurement pump. 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.

[0050] The measurement gas introduced into the second internal space 40 reaches the measurement electrode 44 in the third internal space 61 through the fourth diffusion-controlling part 60 under conditions where the oxygen partial pressure is controlled. Nitrogen oxides in the measurement gas around the measurement electrode 44 are reduced (2NO → N2 + O2) to generate oxygen. This generated oxygen is then pumped by the measurement pump cell 41, and the voltage Vp2 of the variable power supply 46 is controlled so that the voltage V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82 remains constant (target value). Because the amount of oxygen generated around the measurement electrode 44 is proportional to the nitrogen oxide concentration in the measurement gas, the pump current Ip2 in the measurement pump cell 41 is used to calculate the nitrogen oxide concentration in the measurement gas.

[0051] Furthermore, by combining the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 to form an oxygen partial pressure detection means as an electrochemical sensor cell, it is possible to detect an electromotive force corresponding to the difference between the amount of oxygen generated by reduction of the NOx components in the atmosphere around the measurement electrode 44 and the amount of oxygen contained in the reference gas, thereby making it possible to determine the concentration of the NOx components in the measured gas.

[0052] Furthermore, 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 constitute an electrochemical sensor cell 83, and the electromotive force (voltage Vref) obtained by this sensor cell 83 makes it possible to detect the oxygen partial pressure in the measurement gas outside the sensor.

[0053] In the gas sensor 100 having such a configuration, the measurement gas, in which the oxygen partial pressure is always kept at a constant low value (a value that does not substantially affect the measurement of NOx) by operating the main pump cell 21 and the auxiliary pump cell 50, is supplied to the measurement pump cell 41. Therefore, the NOx concentration in the measurement gas can be determined based on the pump current Ip2 that flows when oxygen generated by the reduction of NOx is pumped out of the measurement pump cell 41, which is approximately proportional to the NOx concentration in the measurement gas.

[0054] In order to enhance the oxygen ion conductivity of the solid electrolyte, the sensor element 101 includes a heater unit 70 that adjusts the temperature by heating and maintaining the temperature of the sensor element 101. The heater unit 70 includes a heater connector electrode 71, a heater 72, a through-hole 73, a heater insulating layer 74, and a pressure release hole 75.

[0055] The heater connector electrode 71 is an electrode formed in a manner to contact the lower surface of the first substrate layer 1. By connecting the heater connector electrode 71 to a heater power supply 76 (see FIG. 2), it is possible to supply power from the heater power supply 76 to the heater section 70.

[0056] The heater 72 is an electrical resistor sandwiched between the second substrate layer 2 and the third substrate layer 3. The heater 72 is connected to a heater connector electrode 71 via a through hole 73, and generates heat when power is supplied from a heater power supply 76 through the heater connector electrode 71, thereby heating and keeping warm the solid electrolyte that forms the sensor element 101.

[0057] The heater 72 is embedded throughout the entire area from the first internal space 20 to the third internal space 61, and is capable of adjusting the temperature of the entire sensor element 101 to a temperature at which the solid electrolyte is activated.

[0058] The heater insulating layer 74 is an insulating layer made of an insulator such as alumina and formed on the upper and lower surfaces of the heater 72. The heater insulating layer 74 is formed for the purpose of obtaining electrical insulation between the second substrate layer 2 and the heater 72, and between the third substrate layer 3 and the heater 72.

[0059] The pressure release hole 75 is a portion that penetrates the third substrate layer 3 and the reference gas introduction layer 48 and is provided so as to communicate with the reference gas introduction space 43, and is formed for the purpose of alleviating the increase in internal pressure that accompanies a rise in temperature within the heater insulation layer 74.

[0060] 2, the control device 95 includes the variable power supplies 24, 46, and 52, the heater power supply 76, and a control unit 96. The control unit 96 is a microprocessor including a CPU 97 and a storage unit 98. The storage unit 98 is a rewritable nonvolatile memory capable of storing, for example, various programs and data. The control unit 96 receives the voltage V0 of the oxygen partial pressure detection sensor cell 80 for controlling the main pump, the voltage V1 of the oxygen partial pressure detection sensor cell 81 for controlling the auxiliary pump, the voltage V2 of the oxygen partial pressure detection sensor cell 82 for controlling the measurement pump, 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. The control unit 96 also outputs control signals to the variable power supplies 24, 46, 52 to control the voltages Vp0, Vp1, Vp2 output by 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 also outputs control signals to the heater power supply 76 to control the power supplied from the heater power supply 76 to the heater 72. The memory unit 98 also stores target values ​​V0*, V1*, V2*, etc., which will be described later. The CPU 97 of the control unit 96 controls each of the cells 21, 41, 50 by referring to these target values ​​V0*, V1*, V2*.

[0061] The control unit 96 performs an auxiliary pump control process to control the auxiliary pump cell 50 so that the oxygen concentration in the second internal space 40 becomes a 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 a target value V1*). The target value V1* is set as a value that makes the oxygen concentration in the second internal space 40 a predetermined low concentration that does not substantially affect the measurement of NOx.

[0062] The control unit 96 performs a main pump control process 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 space 40 by the auxiliary pump control process becomes a target current (referred to as a target value Ip1*). Specifically, the control unit 96 sets (feedback controls) a target value (referred to as a 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*. The control unit 96 then feedback controls the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value V0* (i.e., so that the oxygen concentration in the first internal space 20 becomes the target concentration). This main pump control process ensures that the gradient of the oxygen partial pressure in the measurement gas introduced from the third diffusion rate-controlling unit 30 into the second internal space 40 is always constant. The target value V0* is set to a value such that the oxygen concentration in the first internal space 20 is higher but lower than 0%. Furthermore, the pump current Ip0 flowing during this main pump control process varies depending on the oxygen concentration of the measurement gas (i.e., the measurement gas around the sensor element 101) flowing into the measurement gas flow section from the gas inlet 10. Therefore, the control section 96 can also detect the oxygen concentration in the measurement gas based on the pump current Ip0.

[0063] The above-described main pump control process and auxiliary pump control process are also collectively referred to as adjustment pump control process. The first internal space 20 and the second internal space 40 are also collectively referred to as the oxygen concentration adjustment chamber. The main pump cell 21 and the auxiliary pump cell 50 are also collectively referred to as the adjustment pump cell. The control unit 96 performs the adjustment pump control process, causing the adjustment pump cell to adjust the oxygen concentration in the oxygen concentration adjustment chamber.

[0064] Furthermore, the control unit 96 performs a measurement pump control process to control the measurement pump cell 41 so that the voltage V2 becomes a constant value (referred to as a target value V2*) (i.e., so that the oxygen concentration in the third internal space 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*. Oxygen is pumped out of the third internal space 61 by this measurement pump control process.

[0065] By performing the measurement pump control process, oxygen is pumped out of the third internal space 61 so that the amount of oxygen generated by the reduction of NOx in the measurement gas in the third internal space 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 space 61 due to the specific gas (here, NOx), and calculates the NOx concentration in the measurement gas based on this pump current Ip2.

[0066] The storage unit 98 stores a relational expression (for example, a linear or 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 experiment.

[0067] The control unit 96 performs heater control processing, which outputs a control signal to the heater power supply 76 to control the temperature of the heater 72 to a target temperature (e.g., 800°C). Here, the temperature of the heater 72 can be expressed as a linear function of the resistance of the heater 72. Therefore, in the heater control processing, the control unit 96 calculates the resistance of the heater 72 as a value that can be regarded as the temperature of the heater 72 (a value that can be converted to temperature), and feedback-controls the heater power supply 76 so that the calculated resistance becomes the target resistance (the resistance corresponding to the target temperature). The control unit 96 can, for example, acquire the voltage of the heater 72 and the current flowing through the heater 72 and calculate the resistance of the heater 72 based on the acquired voltage and current. The control unit 96 may calculate the resistance of the heater 72 using, for example, a three-terminal method or a four-terminal method. When energizing the heater 72, the heater power supply 76 adjusts the power supplied to the heater 72 by, for example, changing the value of the voltage applied to the heater 72 based on a control signal from the control unit 96.

[0068] The control device 95, including the variable power supplies 24, 46, 52 and heater power supply 76 shown in FIG. 2, is actually connected to each electrode inside the sensor element 101 via lead wires (not shown) formed within the sensor element 101 and connector electrodes (not shown) formed on the rear end side of the sensor element 101 (only the heater connector electrode 71 is shown in FIG. 1).

[0069] The first diffusion rate-controlling section 11 will now be described in detail. The first diffusion rate-controlling section 11 is located upstream of the first internal space 20, the second internal space 40, and the third internal space 61 in the measurement gas flow section. As described above, the first diffusion rate-controlling section 11 includes a diffusion rate-controlling section 11a and a diffusion rate-controlling section 11b. As shown in FIG. 2, the diffusion rate-controlling section 11a includes a first space 85a and a first porous body 87a, and the diffusion rate-controlling section 11b includes a second space 85b and a second porous body 87b. Note that the first porous body 87a and the second porous body 87b are not shown in FIG. 1. The first and second space sections 85a and 85b and the first and second porous bodies 87a and 87b allow the measurement gas to flow in the forward and backward directions (first directions). In this embodiment, the diffusion rate-controlling section 11b (second spatial section 85b and second porous body 87b) has the same configuration as the diffusion rate-controlling section 11a (first spatial section 85a and first porous body 87a), so detailed explanation of the diffusion rate-controlling section 11b will be omitted and only the diffusion rate-controlling section 11a will be explained.

[0070] The first porous body 87a is provided so as to occupy a portion of the cross section of the diffusion rate-controlling section 11a perpendicular to the front-rear direction. The first porous body 87a allows the measurement gas to pass through. The first space 85a is the portion of the cross section of the diffusion rate-controlling section 11a perpendicular to the front-rear direction that is not occupied by the first porous body 87a. The first porous body 87a is provided so as to occupy the lower half of the diffusion rate-controlling section 11a, and the first space 85a is the upper half of the diffusion rate-controlling section 11b. The cross sections perpendicular to the front-rear direction of the diffusion rate-controlling section 11a, the first space 85a, and the first porous body 87a are all substantially rectangular. Note that "rectangle" means a quadrangle with all four equal corners, including a square. However, in this embodiment, the cross sections perpendicular to the front-rear direction of the diffusion rate-controlling section 11a, the first space 85a, and the first porous body 87a are each longer in the left-right direction than in the up-down direction. The first porous body 87a may be disposed in the diffusion rate-controlling section 11a so as to occupy 30% to 70% of the cross section perpendicular to the front-rear direction of the diffusion rate-controlling section 11a. In this embodiment, as shown in Fig. 5, the first porous body 87a occupies 50% of the cross section of the diffusion rate-controlling section 11a. In this embodiment, the first porous body 87a is provided from the front end to the rear end of the diffusion rate-controlling section 11a. Furthermore, the first space section 85a and the first porous body 87a have the shape shown in Fig. 5 in the cross section perpendicular to the front-rear direction at any part of the diffusion rate-controlling section 11a in the front-rear direction.

[0071] The first porous body 87a is made of a ceramic porous body such as a porous alumina body, a porous zirconia body, a porous spinel body, a porous cordierite body, a porous titania body, a porous magnesia body, etc. In this embodiment, the first porous body 87a is made of a porous alumina body.

[0072] In this manner, the diffusion rate-controlling unit 11a has the first space 85a and the first porous body 87a, and therefore, in a cross section perpendicular to the front-rear direction of the diffusion rate-controlling unit 11a, the flow rate of the measurement gas passing through the first porous body 87a can be made different from that of the measurement gas passing through the first space 85a. Specifically, the flow rate of the measurement gas passing through the first porous body 87a is slower than that of the measurement gas passing through the first space 85a. This can cause turbulence in the measurement gas after passing through the first space 85a and the first porous body 87a. In this embodiment, the measurement gas passing through the first space 85a and the measurement gas passing through the first porous body 87a merge in the buffer space 12 downstream of the diffusion rate-controlling unit 11a, causing turbulence in the measurement gas in the buffer space 12. This turbulence in the measurement gas can increase the pressure loss of the measurement gas. Similarly, the diffusion-controlling section 11b having the second spatial section 85b and the second porous body 87b also increases the pressure loss of the measurement gas. This reduces the influence of the dynamic pressure of the measurement gas on the main pump cell 21, which has the inner pump electrode 22 located downstream of the first diffusion-controlling section 11. For example, even if the composition of the measurement gas is the same, different values ​​of the dynamic pressure of the measurement gas may cause the operation of the main pump cell 21 (e.g., the value of the pump current Ip0 flowing through the main pump cell 21) to differ. As a result, the dynamic pressure of the measurement gas may affect the detection accuracy of the specific gas concentration. In contrast, the first diffusion-controlling section 11 of this embodiment increases the pressure loss of the measurement gas by the first and second spatial sections 85a and 85b and the first and second porous bodies 87a and 87b, thereby reducing the influence of the dynamic pressure of the measurement gas on the main pump cell 21. In addition, not only the main pump cell 21 but also the auxiliary pump cell 50 and the measurement pump cell 41 have an auxiliary pump electrode 51 and a measurement electrode 44 provided downstream of the first diffusion-controlling section 11, so the influence of the dynamic pressure of the gas to be measured on the auxiliary pump cell 50 and the measurement pump cell 41 can also be suppressed.

[0073] The first porous body 87a may have any porosity as long as the measurement gas can pass through it, but may have a porosity of 10% or more, for example. The porosity of the first porous body 87a may be 15% or less. If the porosity of the first porous body 87a is 15% or less, the flow rate of the measurement gas passing through the first porous body 87a and the flow rate of the measurement gas passing through the first space portion 85a can be made to be more different, thereby increasing the pressure loss of the measurement gas after passing through. The same applies to the porosity of the second porous body 87b.

[0074] The first space 85a, the second space 85b, the first porous body 87a, and the second porous body 87b of the first diffusion rate-controlling section 11 are present in the same cross section perpendicular to the front-rear direction and form parallel flow paths. The measurement gas that has passed through the diffusion rate-controlling section 11a and the measurement gas that has passed through the diffusion rate-controlling section 11b join together in the buffer space 12 downstream of the first diffusion rate-controlling section 11.

[0075] Next, an example of a manufacturing method for the sensor element 101 of the gas sensor 100 is described below. First, six unsintered ceramic green sheets containing an oxygen-ion conductive solid electrolyte as a ceramic component are prepared. These green sheets are pre-formed with a plurality of sheet holes and necessary through-holes for positioning during printing and lamination. Furthermore, the green sheets that will become the spacer layer 5 are pre-formed with spaces to serve as the measurement gas flow sections by punching or other processes. More specifically, the green sheets that will become the spacer layer 5 are punched so as to leave the first to fourth bridge sections 5a to 5d, thereby providing spaces to serve as the buffer space 12, the first internal void 20, the second internal void 40, and the third internal void 61. Similarly, the green sheets that will become the first solid electrolyte layer 4 are pre-formed with spaces to serve as the reference gas introduction space 43. Then, pattern printing and drying processes are performed to form various patterns on each ceramic green sheet corresponding to 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. Specifically, the formed patterns include, for example, the patterns of each electrode, such as the measurement electrode 44, the lead wires connected to each electrode, connector electrodes, such as the heater connector electrode 71, the reference gas introduction layer 48, and the heater section 70. The pattern printing is performed by applying a pattern-forming paste, prepared according to the characteristics required for each formation target, to the green sheets using a known screen printing technique. The drying process is also performed using a known drying method. After the pattern printing and drying processes are completed, an adhesive paste is printed and dried to laminate and bond the green sheets corresponding to each layer. Next, a lamination process is performed in which the green sheets coated with the adhesive paste are stacked in a predetermined order while being positioned using the sheet holes. Next, a compression process is performed by applying predetermined temperature and pressure conditions to the stacked multiple green sheets to form a single laminate. The laminate obtained in this manner contains a plurality of sensor elements 101. The laminate is cut into pieces of the size of the sensor elements 101. Then, the laminate is subjected to a firing process in which it is fired at a predetermined firing temperature, thereby obtaining the sensor elements 101.

[0076] Here, a method for fabricating the first diffusion rate-controlling portion 11 of the sensor element 101 will be described. FIG. 6 is a partial cross-sectional view showing the fabrication process of the diffusion rate-controlling portion 11a. Since the diffusion rate-controlling portion 11b can be fabricated using the same fabrication method as the diffusion rate-controlling portion 11a, detailed description of the fabrication method for the diffusion rate-controlling portion 11b will be omitted, and only the fabrication method for the diffusion rate-controlling portion 11a will be described. First, as shown in FIG. 6A, in the pattern printing process described above, a porous material layer 187a that will become the first porous body 87a is printed and formed on the upper surface of the bridge portion 105a (the portion corresponding to the first bridge portion 5a) of the green sheet 105 that will become the spacer layer 5. The porous material layer 187a is formed using, for example, a paste containing the material of the first porous body 87a described above (alumina in this embodiment), a pore-forming material, a solvent, a binder, and the like. The porosity of the first porous body 87a can be adjusted by adjusting the content of the pore-forming material in the porous material layer 187a. Next, the vanishing material layer 185a is printed on the upper surface of the porous material layer 187a. The vanishing material layer 185a is a layer for forming the first space portion 85a, and is formed using a paste containing a material (e.g., theobromine) that is burned and eliminated in the firing process described above. After printing in this manner, the lamination process described above is performed, and the green sheet 106 that will become the second solid electrolyte layer 6 is laminated on the vanishing material layer 185a as shown in FIG. 6A.

[0077] By performing the above-described pressure bonding process from the state shown in FIG. 6A, a laminate is produced, resulting in the state shown in FIG. 6B. In the laminate, as shown in FIG. 6B, the upper surface of green sheet 105 and the lower surface of green sheet 106 are softer than porous material layer 187a and vanishing material layer 185a, and are therefore recessed, with green sheets 105 and 106 surrounding them from above, below, left, and right. The viscosity (hardness) of green sheets 105 and 106 can be adjusted, for example, by the type and content of the binder and plasticizer contained therein. The viscosity (hardness) of porous material layer 187a and vanishing material layer 185a can be adjusted, for example, by the solid content ratio and binder content of the paste used for printing them. Adjusting these viscosities (hardness) allows green sheets 105 and 106 to be recessed, as shown in FIG. 6B.

[0078] The laminate is then cut into pieces the size of sensor elements 101, and the cut laminates are subjected to the above-described firing process. As shown in FIG. 6C, the vanishing material layer 185a is burned and disappears, leaving first space portions 85a. The porous material layer 187a is fired to become first porous bodies 87a. The green sheets 105 and 106, which include the bridging portions 105a, are fired to become spacer layers 5 and second solid electrolyte layers 6, each including a first bridging portion 5a. This produces a diffusion-controlling portion 11a having first space portions 85a and first porous bodies 87a.

[0079] Here, the correspondence between the components of this embodiment and the components of the present invention will be clarified. Each of the layers 1 to 6 of this embodiment corresponds to a solid electrolyte layer of the present invention, the element body 102 corresponds to the element body, the first internal space 20, the second internal space 40, and the third internal space 61 correspond to internal spaces, the inner pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44 correspond to inner electrodes, the outer pump electrode 23 corresponds to an outer electrode, the main pump cell 21, the auxiliary pump cell 50, and the measurement pump cell 41 correspond to pump cells, the first diffusion-controlling section 11 (diffusion-controlling section 11a and diffusion-controlling section 11b) corresponds to a diffusion-controlling section, the first and second porous bodies 87a and 87b correspond to porous bodies, and the first and second space sections 85a and 85b correspond to space sections.

[0080] In the sensor element 101 included in the gas sensor 100 of this embodiment described above, the first diffusion-controlling portion 11 includes, at least in a portion in the front-rear direction (first direction), first and second porous bodies 87a, 87b that are provided so as to occupy a portion of a cross section perpendicular to the front-rear direction and through which the measurement gas can pass, and first and second spatial portions 85a, 85b that include portions of the cross section that are not occupied by the first and second porous bodies 87a, 87b and through which the measurement gas can pass. This makes it possible to make the flow rates of the measurement gas passing through the first and second porous bodies 87a, 87b and the first and second spatial portions 85a, 85b different in the cross section perpendicular to the front-rear direction of the first diffusion-controlling portion 11, thereby generating turbulence in the measurement gas after passing through and increasing the pressure loss of the measurement gas. Therefore, the influence of the dynamic pressure of the measurement gas on the main pump cell 21, the auxiliary pump cell 50, and the measurement pump cell 41 provided downstream of the first diffusion rate-controlling section 11 can be suppressed.

[0081] Furthermore, by setting the porosity of the first porous body 87a to 15% or less, the flow rate of the measurement gas passing through the first porous body 87a and the flow rate of the measurement gas passing through the first and second spaces 85a, 85b can be made to differ more, thereby further increasing the pressure loss of the measurement gas after passing through.The same effect can be obtained by setting the porosity of the second porous body 87b to 15% or less.

[0082] It goes without saying that the present invention is not limited to the above-described embodiment, and can be embodied in various forms as long as they fall within the technical scope of the present invention.

[0083] For example, in the above-described embodiment, the diffusion rate-controlling section 11a has one first space 85a and one first porous body 87a, but it may have a plurality of spaces and / or porous bodies. For example, as shown in FIG. 7, the diffusion rate-controlling section 11a may have spaces 85a1, 85a2 and porous bodies 87a1, 87a2 arranged alternately in the left-right direction. The plurality of spaces 85a1, 85a2 exist in the same cross section perpendicular to the front-rear direction and form parallel flow paths. The plurality of porous bodies 87a1, 87a2 exist in the same cross section perpendicular to the front-rear direction and form parallel flow paths.

[0084] In the above-described embodiment, the first space 85a and the first porous body 87a both have a rectangular cross section perpendicular to the front-rear direction, but this is not limited thereto. For example, the embodiment shown in FIG. 8 may be employed. In FIG. 8, the first space 85a and the first porous body 87a have a rectangular cross section perpendicular to the front-rear direction with the long sides curved. Specifically, in the cross section perpendicular to the front-rear direction, the first space 85a has first to fourth portions 86a to 86d as the outer periphery of the cross section. The first portion 86a, the second portion 86b, the third portion 86c, and the fourth portion 86d correspond to the upper, lower, left, and right sides of the outer periphery of the cross section of the first space 85a. The first portion 86a and the second portion 86b face each other in the vertical direction (stacking direction) and extend along the left-right direction (second direction), respectively. The third portion 86c and the fourth portion 86d face each other in the left-right direction and extend along the vertical direction, respectively. The first portion 86a and the second portion 86b are both curved. The first portion 86a and the second portion 86b are curved so as to form a convex shape on the same side in the vertical direction (here, the downward side). The third portion 86c and the fourth portion 86d are both linear shapes along the vertical direction. The cross section of the first space portion 85a is longer in the left-right direction than in the up-down direction. The first porous body 87a has a shape similar to that of the first space portion 85a. Furthermore, like the first space portion 85a and the first porous body 87a, the entire diffusion rate-controlling portion 11a has a cross section perpendicular to the front-to-rear direction that has a rectangular shape with the long sides curved.

[0085] In the embodiment of FIG. 8, the element body 102 has a structural portion 88 that constitutes at least a portion of the outer periphery of the diffusion rate-controlling portion 11a (the outer wall of the diffusion rate-controlling portion 11a). The structural portion 88 has a first structural portion 88a, a second structural portion 88b, and a third structural portion 88c. The first structural portion 88a is disposed on the lower surface of the second solid electrolyte layer 6. In a cross section perpendicular to the front-rear direction, the first structural portion 88a is thin at both left and right ends and becomes thicker toward the left-right center. As a result, the lower surface is curved to form a downwardly convex shape, constituting the upper edge of the diffusion rate-controlling portion 11a, i.e., the first portion 86a of the first space portion 85a. The second structural portion 88b and the third structural portion 88c are disposed on the upper surface of the spacer layer 5. In a cross section perpendicular to the front-rear direction, the second structural portion 88b is thick at the left end and becomes thinner toward the left-right center. In a cross section perpendicular to the front-rear direction, the third structural portion 88c is thicker at its right end and thinner toward the center. As a result, the second structural portion 88b and the third structural portion 88c are curved so that the upper surface is convex downward, forming the shape of the lower edge of the diffusion-controlling portion 11a, i.e., the lower edge of the first porous body 87a. The linear left and right edges of the diffusion-controlling portion 11a (including the third portion 86c and the fourth portion 86d of the first spatial portion 85a) are formed by the spacer layer 5 and the second solid electrolyte layer 6, rather than the structural portion 88. The structural portion 88 is made of a dense material that does not allow the measurement gas to flow through, and in this embodiment, is made of alumina ceramics. The first spatial portion 85a, the first porous body 87a, and the structural portion 88 all have the same cross-sectional shape perpendicular to the front-rear direction (the shape shown in FIG. 8 ).

[0086] The first space 85a in FIG. 8 has a cross section perpendicular to the front-rear direction, which has a predetermined shape with a longer periphery than the reference rectangle. The reference rectangle will be described with reference to FIG. 9. First, consider the circumscribing rectangle R of the cross section of the first space 85a, which is composed of two sides parallel to the vertical direction and two sides parallel to the horizontal direction (upper part of FIG. 9). Next, this circumscribing rectangle R is modified by shortening the short sides while maintaining the length of the long sides so that its area is the same as that of the cross section of the first space 85a, and this rectangle is defined as the reference rectangle S1 (lower part of FIG. 9). Note that if the circumscribing rectangle R is a square, it is sufficient to shorten either one of the two sides parallel to the vertical direction or the two sides parallel to the horizontal direction of the circumscribing rectangle R. The reference rectangle S1 has a shape equivalent to the conventional cross-sectional shape (rectangle) of the space of the diffusion rate-controlling section 11a, and is a rectangle whose area is the same as that of the cross section of the first space 85a so that it can be compared with the first space 85a. The cross section of the first space 85a has the same area as the reference rectangle S1, but because the first portion 86a and the second portion 86b are curved, unlike the reference rectangle S1, the perimeter of the first space 85a is longer than that of the reference rectangle S1. Note that the greater the degree of curvature of the first portion 86a and the second portion 86b, the longer the perimeter of the first space 85a can be. Since the cross section of the first space 85a has a predetermined shape with a perimeter longer than that of the reference rectangle S1, the hydraulic diameter of the first space 85a is smaller than that of the reference rectangle S1. Here, the hydraulic diameter is expressed as four times the value obtained by dividing the cross-sectional area by the wetted perimeter (i.e., the perimeter of the cross section) (hydraulic diameter = cross-sectional area / wetted perimeter × 4). Because the cross-sectional areas of the first space 85a and the reference rectangle S1 are equal, if the outer periphery of the first space 85a (the sum of the lengths of the first to fourth portions 86a to 86d) is longer than the outer periphery of the reference rectangle S1, the hydraulic diameter of the first space 85a will be smaller than that of the reference rectangle S1. The smaller hydraulic diameter increases the pressure loss of the measurement gas passing through the first space 85a.8, the diffusion rate-controlling section 11a not only has the first space 85a and the first porous body 87a, but also has a predetermined shape in cross section perpendicular to the front-rear direction of the first space 85a, which further reduces the influence of the dynamic pressure of the measurement gas on the main pump cell 21, the auxiliary pump cell 50, and the measurement pump cell 41, which are provided downstream of the diffusion rate-controlling section 11a. Note that in the embodiment of FIG. 8, the first porous body 87a and the entire diffusion rate-controlling section 11a also have a predetermined shape in cross section perpendicular to the front-rear direction, just like the first space 85a.

[0087] Note that the pressure loss can also be increased by reducing the cross-sectional area of ​​the first space 85a. For example, if the cross-sectional shape of the first space 85a is the same rectangle as the reference rectangle S1 but the cross-sectional area is reduced, the pressure loss will be higher than that of the reference rectangle S1. However, if the cross-sectional area is reduced, the flow rate of the measurement gas passing through the first space 85a will be reduced. For example, the pump currents Ip0, Ip1, and Ip2 flowing through the main pump cell 21, auxiliary pump cell 50, and measurement pump cell 41 downstream of the first diffusion-controlling section 11 will always be in a small range, which may reduce the detection accuracy of the specific gas concentration of the gas sensor 100. In contrast, in the diffusion-controlling section 11a shown in FIG. 8, the cross-section of the first space 85a has a predetermined shape, which allows the pressure loss to be increased without reducing the cross-sectional area of ​​the first space 85a compared to a conventional shape such as the reference rectangle S1. Therefore, the flow rate of the measurement gas passing through the diffusion rate-controlling portion 11a can be maintained, and the influence of the dynamic pressure of the measurement gas on the main pump cell 21 and the like can be suppressed.

[0088] Note that a definition of the reference rectangle may be different from the reference rectangle S1 shown in Fig. 9. For example, as shown in Fig. 10, a rectangle obtained by modifying the circumscribing rectangle R (upper part of Fig. 10) of the first space portion 85a while maintaining the ratio of each side so that the area is the same as the cross section of the first space portion 85a may be used as the reference rectangle S2 (lower part of Fig. 10). Alternatively, a rectangle obtained by modifying the length of each side of the circumscribing rectangle R so that the area is the same as the cross section of the first space portion 85a and the overlap area with the cross section of the first space portion 85a is maximized may be used as the reference rectangle S3 (not shown). Note that the reference rectangle S3 may end up having the same shape as the reference rectangle S1 or the reference rectangle S2. If the cross-sectional shape of the first space 85a perpendicular to the front-rear direction has a predetermined shape in which the perimeter is longer than at least one of the reference rectangles S1 to S3 defined in this way, the hydraulic diameter of the first space 85a will be smaller than that of the reference rectangle, and therefore the first space 85a can be said to have a shape in which the pressure loss of the measurement gas passing through it will be high. In the first space 85a shown in Fig. 8, the degree of curvature of the first portion 86a and the second portion 86b is determined so that the cross-sectional shape has a predetermined shape in which the perimeter is longer than any of the reference rectangles S1 to S3.

[0089] A method for fabricating the diffusion rate-controlling portion 11a in FIG. 8 will be described with reference to FIG. 11. First, as shown in FIG. 11A, in the pattern printing process described above, second structural material layers 188b and third structural material layers 188c, which will become second structural portions 88b and third structural portions 88c, are printed and formed on the upper surfaces of bridge portions 105a (portions corresponding to first bridge portions 5a) of green sheet 105, which will become spacer layer 5. Second structural material layer 188b and third structural material layer 188c are formed using a paste containing, for example, alumina as a ceramic component. Second structural material layer 188b and third structural material layer 188c may be made of a paste of the same material as porous material layer 187a, except that they do not contain a pore-forming material. The second structural material layer 188b and the third structural material layer 188c are formed so that their thicknesses tend to decrease toward the center on the left and right sides, so that their upper surfaces will have a shape corresponding to the curved shape of the lower edge of the first porous body 87a and the second portion 86b of the first space 85a after the pressure-bonding process. In FIG. 11A , the second structural material layer 188b and the third structural material layer 188c are formed on the upper surface of the first bridge portion 5a at positions corresponding to the left and right ends of the diffusion rate-controlling portion 11a, and no structural material layer is formed in the region near the center on the left and right sides of the diffusion rate-controlling portion 11a. Next, a porous material layer 187a is printed on the upper surface of the green sheet 105, covering the region from the left end of the second structural material layer 188b to the right end of the third structural material layer 188c, and a vanishing material layer 185a is formed on the upper surface of the porous material layer 187a. Then, a first structural material layer 188a, which will become the first structural portion 88a, is printed on the upper surface of the vanishing material layer 185a. Like the second and third structural material layers 188b and 188c, the first structural material layer 188a is formed using a paste containing, for example, alumina as a ceramic component. The first structural material layer 188a is formed so that its thickness increases toward the center so that its underside conforms to the curved shape of the first portion 86a of the first space 85a after the pressure-bonding process. In FIG. 11A, the width of the first structural material layer 188a is smaller than the width of the vanishing material layer 185a, so that the first structural material layer 188a is not formed in positions corresponding to the left and right ends of the first space 85a. After printing is performed in this manner, the lamination process described above is performed, and the green sheet 106 that will become the second solid electrolyte layer 6 is laminated on the first structural material layer 188a as shown in FIG. 11A.

[0090] 11A, the laminate is produced by the above-described pressure bonding process, resulting in the state shown in FIG. 11B. In the laminate, as shown in FIG. 11B, the upper surface of green sheet 105 and the lower surface of green sheet 106 are softer than vanishing material layer 185a, porous material layer 187a, and first to third structural material layers 188a to 188c, so they are recessed, and green sheets 105 and 106 surround them from above, below, left, and right. Furthermore, vanishing material layer 185a, porous material layer 187a, and first to third structural material layers 188a to 188c are deformed by being pressed from above and below by green sheets 105 and 106, so that vanishing material layer 185a takes the shape of first space portion 85a, porous material layer 187a takes the shape of first porous body 87a, and first to third structural material layers 188a to 188c take the shapes of first to third structural portions 88a to 88c. The viscosity of the first to third structural material layers 188a to 188c can be adjusted in the same manner as the viscosity of the porous material layer 187a and the vanishing material layer 185a.

[0091] The laminate is then cut into pieces the size of sensor elements 101, and the cut laminate is subjected to the firing process described above. As shown in FIG. 11C, the vanishing material layer 185a is burned and disappears, leaving the first space portion 85a. The green sheets 105 and 106, each including the bridging portion 105a, are fired to become the spacer layer 5 and the second solid electrolyte layer 6, each including the first bridging portion 5a. The porous material layer 187a is fired to become the first porous body 87a. The first to third structural material layers 188a to 188c are fired to become the first to third structural portions 88a to 88c. This produces a diffusion-controlling portion 11a having the first space portion 85a and the first porous body 87a, each having a predetermined shape in cross section perpendicular to the front-rear direction.

[0092] In Figure 8, the first portion 86a and the second portion 86b of the first space portion 85a are both curved, but when the cross-sectional shape of the first space portion 85a is made the above-mentioned specified shape (a shape whose outer periphery is longer than at least one of the reference rectangles S1 to S3), the cross-sectional shape of the first space portion 85a can be made in various forms.

[0093] For example, one of the first portion 86a and the second portion 86b may be curved and the other linear. In the modified diffusion rate-controlling portion 11a shown in FIG. 12, the first portion 86a is curved and the second portion 86b is linear. In FIG. 12, the upper side of the first porous body 87a is linear and the lower side is curved. The diffusion rate-controlling portion 11a in FIG. 12 can be produced, for example, by forming the vanishing material layer 185a in FIG. 11A so that its thickness tends to decrease toward the center, and by forming the porous material layer 187a so that its thickness tends to increase toward the center. For example, by forming the vanishing material layer 185a by multiple printing operations and forming the center portions of the vanishing material layer 185a by fewer printing operations than the other portions, the thickness of the vanishing material layer 185a can be made different in parts, making the center portions thinner.

[0094] In FIG. 8 , the first portion 86a of the first space 85a is entirely curved. However, at least a portion of the first portion 86a may be curved, such as by combining a straight line with a curved line. The same applies to the second portion 86b. In FIG. 8 , both the first portion 86a and the second portion 86b are curved so as to be convex downward. However, at least one of the first portion 86a and the second portion 86b may be curved so as to be convex upward. In FIG. 8 , the first portion 86a and the second portion 86b are curved so as to be convex on the same vertical direction. However, this is not limited to this. For example, as shown in FIG. 13 , the first portion 86a and the second portion 86b may be convex on the sides that approach each other in the vertical direction. Alternatively, as shown in FIG. 14 , the first portion 86a and the second portion 86b may be convex on the sides that move away from each other in the vertical direction. Furthermore, at least a portion of the first portion 86a and / or at least a portion of the second portion 86b may be polygonal rather than curved. For example, as shown in Fig. 15, the first portion 86a may be formed in a polygonal shape having two bent portions, and the second portion 86b may be formed in a linear shape. In these cases, too, the cross section of the first space 85a perpendicular to the front-rear direction has the above-mentioned predetermined shape (a shape with a longer periphery than at least one of the reference rectangles S1 to S3), thereby further suppressing the influence of the dynamic pressure of the measurement gas on the main pump cell 21 and the like provided downstream of the diffusion rate-controlling portion 11a. Note that the cross section of the first space 85a in Fig. 15 perpendicular to the front-rear direction is formed in a polygonal shape with five or more sides (here, a hexagonal shape).

[0095] An embodiment shown in FIG. 16 may be employed. In the embodiment of FIG. 16, the sensor element 101 has a structural portion 88 similar to that of FIG. 12, and the diffusion rate-controlling portion 11a has spaces 85a1 and 85a2 and porous bodies 87a1 and 87a2 arranged alternately in the left-right direction, similar to that of FIG. 7. In the diffusion rate-controlling portion 11a of FIG. 16, the spaces 85a1 and 85a2 each have a curved shape such that the upper side (first portion) and the lower side (second portion) are convex downward, and the cross section perpendicular to the front-rear direction has the predetermined shape described above. Note that in the embodiment of FIG. 16, the porous bodies 87a1 and 87a2 and the entire diffusion rate-controlling portion 11a also have a cross section perpendicular to the front-rear direction that has the predetermined shape, similar to the spaces 85a1 and 85a2.

[0096] The first space 85a may be divided into multiple spaces by the first porous body 87a. For example, as shown in FIGS. 17 and 18, the first space 85a may be divided into two spaces, an upper space 85a1 and a lower space 85a2, by the first porous body 87a. In FIG. 17, the space 85a1 has a curved shape such that the upper side (first portion) is convex downward, similar to the first space 85a in FIG. 12, and a cross section perpendicular to the front-rear direction has the predetermined shape described above. The upper side of the space 85a1 is formed by the lower surface of the first structural portion 88a. The lower side (second portion) and left and right sides of the space 85a1 are all linear. The lower side of the space 85a1 is formed by the upper surface of the first porous body 87a. The space 85a2 has a curved shape such that the lower side (second portion) is convex upward, and a cross section perpendicular to the front-rear direction has the predetermined shape described above. The lower side of the space 85a2 is defined by the upper surface of the second structural portion 88b. The upper side (first portion) and both left and right sides of the space 85a2 are linear. In FIG. 18, the space 85a1 has a curved shape with its upper side (first portion) convex upward, and its cross section perpendicular to the front-rear direction has the predetermined shape described above. The upper side of the space 85a1 is defined by the lower surfaces of the first structural portion 88a and the fourth structural portion 88d. The space 85a2 has a curved shape with its lower side (second portion) convex downward, and its cross section perpendicular to the front-rear direction has the predetermined shape described above. The lower side of the space 85a2 is defined by the upper surfaces of the second structural portion 88b and the third structural portion 88c. The diffusion rate-controlling portion 11a in FIG. 18 is otherwise configured similarly to the diffusion rate-controlling portion 11a in FIG. 17. The above-mentioned FIGS. 7 and 16 can also be said to be examples of an embodiment in which the first space portion 85a is divided into a plurality of spaces by the first porous body 87a.

[0097] In FIG. 8, the third portion 86c and the fourth portion 86d of the first space 85a are linear along the up-down direction in a cross section perpendicular to the front-rear direction. However, this is not limited thereto. For example, as shown in FIG. 19, the third portion 86c and the fourth portion 86d may be curved. In FIG. 19, the third portion 86c and the fourth portion 86b are curved so as to have a convex shape on the side separating them in the left-right direction. For example, by adjusting the viscosity of the green sheets 105 and 106, the vanishing material layer 185a, the porous material layer 187a, and the first to third structural material layers 188a-188c shown in FIG. 11A, the vanishing material layer 185a, the porous material layer 187a, and the first to third structural material layers 188a-188c can be deformed to bulge left and right during the pressure bonding process, thereby forming the first space 85a having the shapes of the third portion 86c and the fourth portion 86d shown in FIG. 19.

[0098] When the cross-sectional shape of the first space 85a is the above-mentioned predetermined shape (a shape having a longer periphery than at least one of the reference rectangles S1 to S3), the first space 85a has the first to fourth portions 86a to 86d in the above-mentioned modified example, but is not limited to this. For example, in Fig. 14, the first space 85a does not have the third portion 86c and the fourth portion 86d, and the cross-sectional outer periphery of the first space 85a may have a shape in which the first portion 86a and the second portion 86b are directly connected at both left and right ends.

[0099] In the above-described embodiment, the diffusion rate-controlling section 11a has the same cross section perpendicular to the front-rear direction (the shape shown in FIG. 5) at all portions in the front-rear direction. However, this is not limited thereto, and it is sufficient that the first spatial section 85a and the first porous body 87a are present in the cross section perpendicular to the front-rear direction in at least a portion of the front-rear direction. For example, only the front end (upstream end) of the diffusion rate-controlling section 11a may have the cross section shape shown in FIG. 5, and the first porous body 87a is not present in the cross section perpendicular to the front-rear direction in the other portions, so that the entire cross section is a spatial section. Similarly, when the cross sections of the first spatial section 85a and the spatial sections 85a1 and 85a2 of the diffusion rate-controlling section 11a have the predetermined shape as described above, it is sufficient that the cross sections of at least a portion of the front-rear direction have the predetermined shape.

[0100] Furthermore, the diffusion-controlling portion 11a may be formed so that the cross-sectional area of ​​a cross section perpendicular to the front-rear direction is smaller in at least a portion downstream of the upstream end than in the upstream end. For example, the embodiment shown in FIG. 20 may be adopted. FIG. 20 shows a cross section parallel to the front-rear direction of the diffusion-controlling portion 11a. In FIG. 20, upper and lower contours 86e and 86f of the cross section parallel to the front-rear direction of the diffusion-controlling portion 11a are both curved, and both contours 86e and 86f extend so as to curve in the front-rear direction. Furthermore, the contours 86e and 86f have convex shapes on the sides that approach each other in the up-down direction. As a result, the cross-sectional area of ​​the diffusion-controlling portion 11a perpendicular to the front-rear direction is smallest at the center in the front-rear direction. This increases the pressure loss of the measurement gas passing through the portion of the diffusion-controlling portion 11a whose cross-sectional area is smaller than that of the upstream end (e.g., the center portion in the front-rear direction). Therefore, the shape of the diffusion-controlling portion 11a can also suppress the influence of the dynamic pressure of the measurement gas on the main pump cell 21, the auxiliary pump cell 50, and the measurement pump cell 41, which are provided downstream of the diffusion-controlling portion 11. The shapes of the contours 86e, 86f of the diffusion-controlling portion 11a in Fig. 20 can be adjusted by the shapes of the first to third structural portions 88a to 88c, as with the shapes of the first portion 86a and the second portion 86b. In Fig. 20, not only the entire diffusion-controlling portion 11a but also the first spatial portion 85a and the first porous body 87a are each formed so that the cross-sectional area of ​​the cross section perpendicular to the front-to-rear direction is reduced in at least a portion downstream of the upstream end.

[0101] The embodiment shown in FIG. 21 or 22 may be adopted instead of the embodiment shown in FIG. 20. In FIG. 21, contour 86e has a curved shape formed by connecting two contours 86e of FIG. 20 front and rear, and contour 86f has a curved shape formed by connecting two contours 86f of FIG. 20 front and rear. Therefore, contours 86e and 86f of FIG. 21 have two convex shapes on sides approaching each other in the vertical direction. As a result, in FIG. 21, the diffusion-controlling portion 11a has two smallest cross-sectional areas in a cross section perpendicular to the front and rear direction at midpoints in the front and rear direction (positions other than the front and rear ends), resulting in high pressure loss of the measurement gas passing through these two locations. In FIG. 22, the upper and lower contours 86e and 86f of the diffusion-controlling portion 11a in a cross section parallel to the front and rear direction are both curved, and both contours 86e and 86f extend so as to curve relative to the front and rear direction. Furthermore, contours 86e and 86f have convex shapes on the same side (lower side) in the vertical direction. Furthermore, the vertical distance between the contours 86e and 86f becomes smaller as they approach the rear end compared to the front end. As a result, the cross-sectional area of ​​the diffusion-controlling portion 11a in FIG. 22, taken along a plane perpendicular to the front-rear direction, is smallest at the rear end. This increases the pressure loss of the measurement gas passing through the rear end of the diffusion-controlling portion 11a in FIG. 22. In FIGS. 21 and 22, not only the entire diffusion-controlling portion 11a but also the first space portion 85a and the first porous body 87a are each formed so that the cross-sectional area of ​​the cross-section perpendicular to the front-rear direction becomes small in at least a portion downstream of the upstream end.

[0102] The diffusion-controlling portion 11a shown in Figures 20 to 22 has a first space portion 85a and a first porous body 87a in a cross section perpendicular to the front-to-rear direction in any part in the front-to-rear direction, but there may be a part in the front-to-rear direction where the first porous body 87a is not present (a part where only the first space portion 85a is present).

[0103] In the above-described embodiment, the first diffusion rate-controlling portion 11 includes a diffusion rate-controlling portion 11a provided between the spacer layer 5 and the second solid electrolyte layer 6 and a diffusion rate-controlling portion 11b provided between the spacer layer 5 and the second solid electrolyte layer 6. However, the present invention is not limited to this and may include only one of the diffusion rate-controlling portion 11a and the diffusion rate-controlling portion 11b. Furthermore, the diffusion rate-controlling portion 11a is provided between the adjacent spacer layer 5 and the second solid electrolyte layer 6. However, the present invention is not limited to this and may be formed, for example, by punching out one of the layers constituting the element body 102. For example, the sensor element 101 may include a first diffusion rate-controlling portion 211 shown in FIGS. 23 to 25 instead of the first diffusion rate-controlling portion 11. As shown in FIGS. 23 to 25, the first diffusion rate-controlling portion 211 is formed by punching out the spacer layer 5 from above and below. The first diffusion rate-controlling section 211 is longer in the up-down direction than the diffusion rate-controlling section 11a of the first diffusion rate-controlling section 11, and is therefore configured so that the cross-sectional area perpendicular to the front-to-rear direction is approximately the same as that of the diffusion rate-controlling section 11a by making the length in the left-to-right direction shorter than that of the diffusion rate-controlling section 11a. In addition, the left-to-right length of the first diffusion rate-controlling section 211 is shorter than the left-to-right length of the buffer space 12 (see FIG. 24).

[0104] The first diffusion rate-controlling section 211 has a space 285 and a porous body 287. As shown in FIG. 25, the space 285 and the porous body 287 both have a rectangular cross section perpendicular to the front-rear direction, with the upper and lower sides curved. Specifically, in the cross section perpendicular to the front-rear direction, the space 285 has first to fourth portions 286a to 286d as the outer periphery of the cross section. The first portion 286a, the second portion 286b, the third portion 286c, and the fourth portion 286d correspond to the upper, lower, left, and right sides of the outer periphery of the cross section of the space 285. The first portion 286a and the second portion 286b face each other in the vertical direction (stacking direction) and extend along the left-right direction (second direction), respectively. The third portion 286c and the fourth portion 286d face each other in the left-right direction and extend along the vertical direction, respectively. The first portion 286a and the second portion 286b have the same shape as the first portion 86a and the second portion 86b in FIG. 8. Specifically, the first portion 286a and the second portion 286b are both curved and convex on the same side in the vertical direction (the downward side in this case). The third portion 86c and the fourth portion 86d are both linear along the vertical direction, similar to the third portion 86c and the fourth portion 86d in FIG. 8. The porous body 287 also has the same shape as the space portion 285. Furthermore, like the space portion 285 and the porous body 287, the entire first diffusion rate-controlling portion 211 has a rectangular cross section perpendicular to the front-to-rear direction, with the upper and lower sides curved. The shapes of the upper and lower edges of the first diffusion-controlling section 211, i.e., the shapes of the first portion 286a of the space 285 and the lower edge of the porous body 287, can be adjusted by the shapes of the first to third structural portions 288a to 288c of the structural portion 288, as shown in FIG. 8. Specifically, the first structural portion 288a is disposed on the lower surface of the second solid electrolyte layer 6. In a cross section perpendicular to the front-rear direction, the first structural portion 288a is thin at both left and right ends and becomes thicker toward the center. As a result, the lower surface is curved to form a downwardly convex shape, constituting the first portion 286a of the space 85. The second structural portion 288b and the third structural portion 288c are disposed on the upper surface of the first solid electrolyte layer 4. In a cross section perpendicular to the front-rear direction, the second structural portion 288b is thick at the left and right ends and becomes thinner toward the center.The third structural portion 288c is thicker at the right end in a cross section perpendicular to the front-rear direction and becomes thinner toward the center in the left-right direction. As a result, the second structural portion 288b and the third structural portion 288c as a whole are curved so that the upper surface is convex downward, forming the shape of the lower side of the porous body 287. Note that the structural portion 288 is not shown in Figure 23. The left and right sides of the first diffusion rate-controlling portion 211, which are linear (including the third portion 286c and the fourth portion 286d of the space portion 285), are configured not as structural portions 288 but as the inner circumferential surfaces (side surfaces) of punched holes (holes that vertically penetrate the spacer layer 5) provided in the spacer layer 5. Like the diffusion rate-controlling section 11a of the above-described embodiment, the first diffusion rate-controlling section 211 has a space 285 and a porous body 287. This allows the flow rates of the measurement gas passing through the porous body 287 and the measurement gas passing through the space 285 to differ, thereby generating turbulence in the measurement gas after passage and increasing the pressure loss of the measurement gas. Similarly to the diffusion rate-controlling section 11a of FIG. 8 described above, the first diffusion rate-controlling section 211 has the space 285. The first portion 286a and the second portion 286b of the cross section perpendicular to the front-to-rear direction are curved, so that the cross section has the above-described predetermined shape (a shape whose perimeter is longer than at least one of the reference rectangles S1 to S3). This results in a smaller hydraulic diameter of the space 285 than at least one of the reference rectangles S1 to S3, thereby increasing the pressure loss of the measurement gas passing through the space 285. This achieves the same effect as the first space 85a of FIG. 8 described above. Regarding the shape of the space 285 and the shape of the porous body 287, the various aspects of the first space 85a and the first porous body 87a described above may be adopted.

[0105] In the above-described embodiment, the first diffusion rate-controlling section 11 has first and second porous bodies 87a, 87b and first and second spatial sections 85a, 85b, but this is not limited to this, and one or more of the first diffusion rate-controlling section 11, the second diffusion rate-controlling section 13, the third diffusion rate-controlling section 30, and the fourth diffusion rate-controlling section 60 may have a porous body and a spatial section.

[0106] In the above-described embodiment, the front end of the first diffusion-controlling part 11 is the gas inlet 10, but this is not limiting. For example, the first bridging part 5a and the first diffusion-controlling part 11 may be disposed rearward of the gas inlet 10 in the measurement gas flow part.

[0107] 23, the first diffusion rate-controlling part 11, 211 allows the measurement gas to flow in the front-rear direction, but this is not limited thereto. For example, the gas inlet 10 may be open on the left or right surface of the element body 102, and the first diffusion rate-controlling part 11 may allow the measurement gas to flow in the left-right direction. In this case, the left-right direction corresponds to the first direction, and the front-rear direction corresponds to the second direction.

[0108] In the above-described embodiment, 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 in the auxiliary pump cell 50 (also referred to as an outer auxiliary pump electrode), and an electrode paired with the measurement electrode 44 in the measurement pump cell 41 (also referred to as an outer measurement electrode), but is not limited to this. Any one or more of the outer main pump electrode, the outer auxiliary pump electrode, and the outer measurement electrode may be provided separately from the outer pump electrode 23 on the outer surface of the element body 102 so as to come into contact with the measurement gas.

[0109] In the above-described embodiment, the outer pump electrode 23 is exposed to the outside of the sensor element 101, but this is not limiting and the outer pump electrode 23 may be provided on the outer surface of the element body 102 so as to be in contact with the measurement gas. For example, the sensor element 101 may be provided with a porous protective layer that covers the element body 102 and allows the measurement gas to pass through, and the outer pump electrode 23 may also be covered with the porous protective layer.

[0110] In the above-described embodiment, the sensor element 101 detects the NOx concentration in the measurement gas. However, this is not limiting, as long as it detects the concentration of a specific gas in the measurement gas. For example, the specific gas concentration may be other oxide concentrations, not just NOx. When the specific gas is an oxide, oxygen is generated when the specific gas itself is reduced in the third internal space 61, as in the above-described embodiment. The measurement pump cell 41 can detect the specific gas concentration by obtaining a detection value corresponding to this oxygen (e.g., pump current Ip2). Alternatively, the specific gas may be a non-oxide, such as ammonia. When the specific gas is a non-oxide, the specific gas is converted to an oxide (e.g., ammonia is converted to NO). When the converted gas is reduced in the third internal space 61, oxygen is generated. The measurement pump cell 41 can detect the specific gas concentration by obtaining a detection value corresponding to this oxygen (e.g., pump current Ip2). For example, the inner pump electrode 22 in the first internal space 20 functions as a catalyst, thereby converting ammonia to NO in the first internal space 20.

[0111] In the above-described embodiment, the element body 102 of the sensor element 101 is a laminate including multiple solid electrolyte layers (layers 1 to 6). However, this is not limiting. The element body 102 of the sensor element 101 may include at least one oxygen-ion conductive solid electrolyte layer. For example, in FIG. 1, layers 1 to 5 other than the second solid electrolyte layer 6 may be layers made of a material other than a solid electrolyte (e.g., a layer made of alumina). In this case, the electrodes of the sensor element 101 may be disposed on the second solid electrolyte layer 6. For example, the measurement electrode 44 in FIG. 1 may be disposed on the lower surface of the second solid electrolyte layer 6. Furthermore, the reference gas introduction space 43 may be disposed on the spacer layer 5 instead of on the first solid electrolyte layer 4, the reference gas introduction layer 48 may be disposed between the second solid electrolyte layer 6 and the spacer layer 5 instead of between the first solid electrolyte layer 4 and the third substrate layer 3, and the reference electrode 42 may be disposed behind the third internal space 61 and on the lower surface of the second solid electrolyte layer 6. [Industrial Applicability]

[0112] The present invention can be used in a gas sensor that detects the concentration of a specific gas such as NOx in a measurement gas such as an automobile exhaust gas. [Explanation of symbols]

[0113] 1 first substrate layer, 2 second substrate layer, 3 third substrate layer, 4 first solid electrolyte layer, 5 spacer layer, 5a first bridge portion, 5b second bridge portion, 5c third bridge portion, 6 second solid electrolyte layer, 10 gas inlet, 11 first diffusion rate-controlling portion, 11a diffusion rate-controlling portion, 11b diffusion rate-controlling portion, 12 buffer space, 13 second diffusion rate-controlling portion, 20 first internal cavity, 21 main pump cell, 22 inner pump electrode, 22a ceiling electrode portion, 22b bottom electrode portion, 23 outer pump electrode, 24 variable power supply, 30 third diffusion rate-controlling portion, 40 second internal cavity, 41 measurement pump cell, 42 reference electrode, 43 reference gas introduction space, 44 measurement electrode, 46 variable power supply, 48 reference gas introduction layer, 49 reference gas introduction portion, 49a inlet portion, 50 auxiliary pump cell, 51 Auxiliary pump electrode, 51a ceiling electrode portion, 51b bottom electrode portion, 52 variable power supply, 60 fourth diffusion rate-controlling portion, 61 third internal cavity, 70 heater portion, 71 heater connector electrode, 72 heater, 73 through hole, 74 heater insulating layer, 75 pressure release hole, 76 heater power supply, 80 oxygen partial pressure detection sensor cell for controlling main pump, 81 oxygen partial pressure detection sensor cell for controlling auxiliary pump, 82 oxygen partial pressure detection sensor cell for controlling measurement pump, 83 sensor cell, 85a, 85b first and second space portions, 85a1, 85a2 space portions, 86a to 86d first portion to fourth portion, 86e, 86f contour, 87a, 87b first and second porous bodies, 87a1, 87a2 porous bodies, 88 structural portion, 88a to 88f 1st to 6th structural portions, 95 control device, 96 control portion, 97 CPU, 98 memory portion, 100 gas sensor, 101, 201 sensor element, 102 element body, 105, 106 green sheet, 105a bridging portion, 185a dissipation material layer, 187a porous material layer, 188a to 188c 1st to 3rd structural material layers, 211 1st diffusion-controlling portion, 285 space portion, 286a to 286d 1st to 4th portions, 287 porous body, 288 structural portion, 288a to 288c 1st to 3rd structural portions, R circumscribed rectangle, S1 to S2 reference rectangle.

Claims

1. A sensor element for detecting the concentration of a specific gas in a measurement gas, an element body having an oxygen ion conductive solid electrolyte layer and a measurement gas flow section provided therein for introducing the measurement gas from a gas inlet and flowing the measurement gas in a first direction; a pump cell having an inner electrode provided in an internal space of the measurement gas flow portion and an outer electrode provided on an outer surface of the element body; a diffusion rate-controlling section provided in the measurement gas flow section upstream of the internal space and configured to provide a diffusion resistance to the measurement gas introduced through the gas inlet; Equipped with the diffusion-controlling portion includes a porous body that is provided in at least a part of the first direction so as to occupy a part of a cross section perpendicular to the first direction and through which the measurement gas can pass; and a space portion that includes a part of the cross section that is not occupied by the porous body and through which the measurement gas can pass. Sensor element.

2. 2. The sensor element according to claim 1, The porous body is disposed in the diffusion-controlling portion so as to occupy 30% to 70% of the cross section. Sensor element.

3. 3. The sensor element according to claim 1, The porosity of the porous body is 15% or less. Sensor element.

4. 3. The sensor element according to claim 1, The porous body is provided in plurality so as to form parallel flow paths in the cross section. Sensor element.

5. 3. The sensor element according to claim 1, the element body has a longitudinal direction and is a laminate in which a plurality of layers including the solid electrolyte layer are stacked in a stacking direction perpendicular to the longitudinal direction, The cross-sectional shape of the space portion is a predetermined shape having a perimeter longer than that of a reference rectangle, The reference rectangle has the same area as the cross section of the space portion, and is a rectangle obtained by deforming a circumscribing rectangle of the cross section, which is composed of two sides parallel to the stacking direction and two sides parallel to a second direction perpendicular to the stacking direction, so that the short sides are shortened while maintaining the length of the long sides, or a rectangle obtained by deforming while maintaining the ratio of the sides, or a rectangle obtained by changing the length of the sides so that the overlapping area with the cross section is maximized. Sensor element.

6. 6. The sensor element according to claim 5, the outer periphery of the predetermined shape has a first portion and a second portion that face each other in the stacking direction and extend along the second direction, At least a portion of the first portion and / or at least a portion of the second portion is curved. Sensor element.

7. 6. The sensor element according to claim 5, the outer periphery of the predetermined shape has a first portion and a second portion that face each other in the stacking direction and extend along the second direction, At least a part of the first portion and / or at least a part of the second portion is in a polygonal line shape. Sensor element.

8. 7. The sensor element according to claim 6, the first portion and the second portion have a convex shape on the same side in the stacking direction; Sensor element.

9. 7. The sensor element according to claim 6, the first portion and the second portion have a convex shape on a side where they approach each other or on a side where they are separated from each other in the stacking direction; Sensor element.

10. 6. The sensor element according to claim 5, the diffusion-controlling portion has a plurality of the space portions, Each of the plurality of spaces has the cross-sectional shape of the predetermined shape. Sensor element.

11. 3. The sensor element according to claim 1, the diffusion-controlling portion is formed so that a cross-sectional area of ​​the diffusion-controlling portion perpendicular to the first direction is smaller in at least a portion downstream of the upstream end than in the upstream end. Sensor element.

12. 12. The sensor element according to claim 11, the diffusion-controlling portion extends such that a cross-sectional profile parallel to the first direction is curved with respect to the first direction; Sensor element.

13. A gas sensor comprising the sensor element according to claim 1 or 2.

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