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 comprises a diffusion rate determination unit that applies diffusion resistance to the gas to be measured introduced from a gas introduction port. The diffusion rate determination unit has a first space part 85a that allows the gas to be measured to pass through in a fore-and-aft direction. The shape of a cross section orthogonal to the fore-and-aft direction in at least part of the first space part 85a in the fore-and-aft direction is a predetermined shape with a longer outer periphery than a reference rectangle S1. The reference rectangle S1 is a rectangle having the same area as the cross section of the first space part 85a and is obtained by deforming a circumscribed rectangle R of the cross section formed of two sides parallel in the vertical direction and two sides parallel in the transverse direction orthogonal to the vertical direction, so as to reduce the length of the short sides while maintaining the length of the long sides.SELECTED DRAWING: Figure 6

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 a longitudinal direction, the element body being a laminate formed by laminating a plurality of layers including an oxygen ion conductive solid electrolyte layer in a lamination direction perpendicular to the longitudinal direction, the element body having a measurement gas flow section therein for introducing the measurement gas from a gas inlet and flowing the measurement gas in a first direction; a pump cell including 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 has a space portion through which the measurement gas flows in the first direction, a cross section of the space perpendicular to the first direction in at least a part of the first direction has a predetermined shape whose perimeter is 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 side is shortened while maintaining the length of the long side, or a rectangle obtained by deforming while maintaining the ratio of each side, or a rectangle obtained by changing the length of each side so that the overlapping area with the cross section is maximized. It is something.

[0008] In this sensor element, the diffusion-controlling portion has a space portion through which the measurement gas flows in a first direction. The cross-section of at least a portion of the space portion perpendicular to the first direction in the first direction has a predetermined shape with a longer periphery than a reference rectangle. This reduces the hydraulic diameter of the portion of the space portion of the diffusion-controlling portion that has the predetermined shape compared to the reference rectangle, thereby increasing the pressure loss of the measurement gas passing through the space portion. This reduces the effect of the dynamic pressure of the measurement gas on a pump cell having an inner electrode located downstream of the diffusion-controlling portion.

[0009] [2] In the above-mentioned sensor element (the sensor element described in [1]), 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 at least a part of the second part may be curved.

[0010] [3] In the above-mentioned sensor element (the sensor element described in [1] or [2]), 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.

[0011] [4] In the sensor element described above (the sensor element described in [2] or [3] above), the first portion and the second portion may have a convex shape on the same side in the stacking direction.

[0012] [5] In the sensor element described above (the sensor element described in [2] or [3]), 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.

[0013] [6] In the sensor element described above (the sensor element according to any one of [1] to [5] above), the length of the cross section of the space in the second direction may be greater than the length in the stacking direction.

[0014] [7] In the sensor element described above (the sensor element described in any one of [1] to [6]), the diffusion-controlling portion may have a plurality of the space portions, and each of the plurality of space portions may have the predetermined cross-sectional shape.

[0015] [8] In the sensor element described above (the sensor element described in any one of [1] to [7]), the space may be formed so that the cross-sectional area of ​​the space perpendicular to the first direction is smaller than that of the upstream end in at least a portion downstream of the upstream end. This increases the pressure loss of the measurement gas passing through the portion of the space having the smaller cross-sectional area than that of 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 section.

[0016] [9] In the sensor element described above (the sensor element described in [8] above), the space may extend such that a cross-sectional contour parallel to the first direction is curved with respect to the first direction.

[0017]

[10] A gas sensor according to the present invention includes the sensor element according to any one of the above items [1] to [9]. 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]

[0018] [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] FIG. 10 is an explanatory diagram of a reference rectangle S1. [Figure 7] 10A and 10B are partial cross-sectional views showing a manufacturing process of the first space portion 85a of the first diffusion rate-controlling portion 11. [Figure 8] FIG. 10 is an explanatory diagram of a reference rectangle S2. [Figure 9] FIG. 10 is an explanatory diagram of a first space 85a of a modified example. [Figure 10] FIG. 10 is an explanatory diagram of a first space 85a of a modified example. [Figure 11] FIG. 10 is an explanatory diagram of a first space 85a of a modified example. [Figure 12] FIG. 10 is an explanatory diagram of a first space 85a of a modified example. [Figure 13] FIG. 10 is an explanatory diagram of a first space 85a of a modified example. [Figure 14] FIG. 10 is an explanatory diagram of a first space 85a of a modified example. [Figure 15] FIG. 10 is an explanatory diagram of a first space 85a of a modified example. [Figure 16] FIG. 10 is an explanatory diagram of a first space 85a of a modified example. [Figure 17] FIG. 10 is an explanatory diagram of a first space 85a of a modified example. [Figure 18] FIG. 10 is an explanatory diagram of a first space 85a of a modified example. [Figure 19] FIG. 10 is a cross-sectional schematic view showing a first diffusion rate-controlling part 211 of a modified example. [Figure 20] DD cross section of Figure 19. [Figure 21] EE cross section of Figure 20. DETAILED DESCRIPTION OF THE INVENTION

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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). The shapes of the first space 85a and the second space 85b constituting the two slits of the first diffusion-controlling section 11 are shown in FIGS. 2 and 5. The fourth diffusion-controlling section 60 is provided as a single 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.

[0024] 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.

[0025] 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.

[0026] 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).

[0027] 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 opens at the front end surface of the sensor element 101, and this opening serves as the gas inlet 10. As shown in FIGS. 1 and 2 , the first spatial portion 85a 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 second spatial portion 85b 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 from 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), but 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 rate-controlling section 11, buffer space 12, and second diffusion rate-controlling section 13. As a result, the pressure fluctuations of the measurement gas introduced into the first internal space 20 become 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 part 13. The oxygen partial pressure is adjusted by the operation of the main pump cell 21.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] In the measuring pump cell 41, oxygen generated by decomposition of nitrogen oxides in the atmosphere surrounding the measuring electrode 44 is pumped out, and the amount of oxygen generated can be detected as a pump current Ip2.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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*.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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).

[0066] 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 has the first spatial section 85a and the second spatial section 85b. The first spatial section 85a and the second spatial section 85b allow the measurement gas to flow in the front-rear direction (first direction). In this embodiment, since the second spatial section 85b has the same shape as the first spatial section 85a, detailed description of the second spatial section 85b will be omitted, and only the shape of the first spatial section 85a will be described. As shown in FIG. 5, in a cross section perpendicular to the front-rear direction, the first spatial section 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 edges of the 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 lower side). The third portion 86c and the fourth portion 86d are both linear in the vertical direction. The cross section of the first space 85a is longer in the left-right direction than in the vertical direction.

[0067] The element body 102 has a structural portion 88 that constitutes at least a portion of the outer periphery of the first space portion 85a (the outer wall of the first diffusion rate-controlling portion 11). 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 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 its 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 thick at its right end and becomes thinner toward the left-right center. As a result, the second structural portion 88b and the third structural portion 88c are curved so that the upper surface as a whole is convex downward, constituting the second portion 86b. The linear third portion 86c and fourth portion 86d 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 pass through, and in this embodiment, it is made of alumina ceramics. The structural portion 88 is not shown in Figures 1 and 2. The first spatial portion 85a and the structural portion 88 have the same shape (the shape shown in Figure 5) in the cross section perpendicular to the front-rear direction at any part in the front-rear direction.

[0068] The first space 85a has a cross section perpendicular to the front-rear direction that has a predetermined shape with a longer periphery than the reference rectangle. The reference rectangle will be described with reference to FIG. 6. First, consider a circumscribing rectangle R of the cross section of the first space 85a, which is composed of two sides parallel to the up-down direction and two sides parallel to the left-right direction (upper part of FIG. 6). Next, this circumscribing rectangle R is modified by shortening the short sides while maintaining the length of the long sides so that the area is the same as that of the cross section of the first space 85a, resulting in a reference rectangle S1 (lower part of FIG. 6). The reference rectangle S1 has a shape corresponding to the conventional cross-sectional shape (rectangle) of the space of the first diffusion-controlling section 11, and is a rectangle that is the same area as 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, and because the first portion 86a and the second portion 86b are curved, unlike the reference rectangle S1, the cross section of the first space 85a has a longer periphery than the reference rectangle S1. The greater the degree of curvature of the first portion 86a and the second portion 86b, the longer the outer periphery of the first space 85a can be. Since the cross section of the first space 85a has a predetermined shape with a longer outer periphery than the reference rectangle S1, the first space 85a has a smaller hydraulic diameter than 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 periphery (i.e., the outer periphery of the cross section) (hydraulic diameter = cross-sectional area / wetted periphery × 4). Since 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 is smaller than that of the reference rectangle S1. Furthermore, the smaller hydraulic diameter results in a higher pressure loss of the measurement gas passing through the first space 85a. This makes it possible to suppress the influence of the dynamic pressure of the measurement gas on the main pump cell 21, which has the inner pump electrode 22 provided downstream of the first diffusion-controlling part 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 different behavior of the main pump cell 21 (e.g., the value of the pump current Ip0 flowing through the main pump cell 21). As a result, the dynamic pressure of the measurement gas may affect the detection accuracy of the specific gas concentration.In contrast, in the first diffusion-controlling section 11 of this embodiment, the cross section of the first space 85a is formed in a predetermined shape to increase pressure loss, thereby suppressing the influence of the dynamic pressure of the measurement gas on the main pump cell 21. Since not only the main pump cell 21 but also the auxiliary pump cell 50 and the measurement pump cell 41 have the auxiliary pump electrode 51 and the measurement electrode 44 provided downstream of the first diffusion-controlling section 11, the cross section of the first space 85a is formed in a predetermined shape to suppress the influence of the dynamic pressure of the measurement gas on the auxiliary pump cell 50 and the measurement pump cell 41. The term "rectangle" refers to a quadrangle with four equal corners, including a square. When 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.

[0069] Note that the pressure loss can also be increased by reducing the cross-sectional area. 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 when the reference rectangle S1 is used. However, reducing the cross-sectional area reduces the flow rate of the measurement gas passing through the first diffusion-controlling section 11. This may result in 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 always being in a small range, thereby reducing the detection accuracy of the specific gas concentration of the gas sensor 100. In contrast, in the first diffusion-controlling section 11 of this embodiment, 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 first diffusion rate-controlling part 11 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.

[0070] As described above, the second space portion 85b has the same shape as the first space portion 85a, so that the cross section perpendicular to the front-to-rear direction of each of the first space portion 85a and the second space portion 85b of the first diffusion rate-controlling portion 11 has a predetermined shape.

[0071] 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.

[0072] Here, a method for fabricating the first diffusion rate-controlling portion 11 of the sensor element 101 will be described. FIG. 7 is a partial cross-sectional view showing a fabrication process for the first space 85a of the first diffusion rate-controlling portion 11. Since the second space 85b can be fabricated using the same fabrication method as the first space 85a, a detailed description of the fabrication method for the second space 85b will be omitted, and only the fabrication method for the first space 85a will be described. First, as shown in FIG. 7A, in the pattern printing process described above, a second structural material layer 188b and a third structural material layer 188c, which will become the second structural portion 88b and the third structural portion 88c, are 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, which will become the spacer layer 5. The second structural material layer 188b and the third structural material layer 188c are formed using a paste containing, for example, alumina as a ceramic component. 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 second portion 86b of the first space 85a after the pressure-bonding process. In this embodiment, as shown in FIG. 7A, 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 first space 85a, and no structural material layer is formed in the region near the center on the left and right sides of the first space 85a. Next, a vanishing material layer 185a is printed and formed on the upper surface of the green sheet 105 in a region from the left end of the second structural material layer 188b to the right end of the third structural material layer 188c. The vanishing material layer 185a is a layer for forming the first space 85a and is formed using a paste containing a material (e.g., theobromine) that burns and disappears during the firing process described above. 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 structural material layer 188b and the third structural material layer 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 tends to increase toward the center on both sides, so that its lower surface will have a shape corresponding to the curved shape of the first portion 86a of the first space portion 85a after the pressure-bonding process.In this embodiment, as shown in Fig. 7A, the left and right width of first structural material layer 188a is made smaller than the left and right width of vanishing material layer 185a, so that first structural material layer 188a is not formed in positions corresponding to the vicinity of both left and right ends of first space portion 85a. After printing is performed in this manner, the lamination process described above is performed, and green sheet 106, which will become second solid electrolyte layer 6, is laminated on first structural material layer 188a as shown in Fig. 7A.

[0073] By carrying out the above-described pressure bonding process from the state shown in FIG. 7A, a laminate is produced, resulting in the state shown in FIG. 7B. In the laminate, as shown in FIG. 7B, the upper surface of green sheet 105 and the lower surface of green sheet 106 are softer than vanishing material layer 185a 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 and first to third structural material layers 188a to 188c are pressed from above and below by green sheets 105 and 106, causing them to deform, with vanishing material layer 185a taking on the shape of first space portion 85a and first to third structural material layers 188a to 188c taking on the shapes of first to third structural portions 88a to 88c. The viscosity (hardness) of green sheets 105 and 106 can be adjusted, for example, by the type and content of binders and plasticizers contained therein. The viscosity (hardness) of the vanishing material layer 185a and the first to third structural material layers 188a to 188c can be adjusted, for example, by the solid content ratio and binder content of the paste used for printing them. By adjusting these viscosities (hardness), it is possible to make the green sheets 105 and 106 recessed as shown in FIG. 7B.

[0074] The laminate is then cut into pieces the size of sensor elements 101, and the cut laminate is subjected to the above-described firing process, whereby, as shown in FIG. 7C, the vanishing material layer 185a is burned and eliminated, 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 second solid electrolyte layer 6, each including the first bridging portion 5a. 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 the first diffusion-controlling portion 11 having the first space portion 85a.

[0075] Here, the correspondence between the components of this embodiment and the components of the present invention will be clarified. In this embodiment, the layers 1 to 6 correspond to the solid electrolyte layers 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 the internal spaces; the inner pump electrode 22, the auxiliary pump electrode 51, and the measurement electrode 44 correspond to the inner electrodes; the outer pump electrode 23 corresponds to the outer electrode; the main pump cell 21, the auxiliary pump cell 50, and the measurement pump cell 41 correspond to the pump cells; the first diffusion-controlling section 11 corresponds to the diffusion-controlling section; and the first and second spaces 85a and 85b correspond to the spaces. The first portion 86a corresponds to the first portion, and the second portion 86b corresponds to the second portion.

[0076] In the sensor element 101 of the gas sensor 100 of this embodiment described above, the first diffusion-controlling section 11 has a first space 85a through which the measurement gas flows in the front-rear direction (first direction). The cross-section of the first space 85a perpendicular to the front-rear direction has a predetermined shape with a longer outer periphery than the reference rectangle S1. This reduces the hydraulic diameter of the first space 85a compared to the reference rectangle S1, thereby increasing the pressure loss of the measurement gas passing through the first space 85a. This 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 located downstream of the diffusion-controlling section 11. Similarly, the cross-section of the second space 85b perpendicular to the front-rear direction has a predetermined shape with a longer outer periphery than the reference rectangle S1. This increases the pressure loss of the measurement gas passing through the second space 85b, achieving the same effect as the first space 85a.

[0077] 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.

[0078] For example, in the above-described embodiment, the reference rectangle S1 was defined as a rectangle obtained by shortening the short sides of the circumscribing rectangle R while maintaining the length of the long sides so that the area of ​​the circumscribing rectangle R was the same as that of the cross section of the first space portion 85a. However, the reference rectangle may be defined differently. For example, as shown in FIG. 8, the reference rectangle S2 may be defined as a rectangle obtained by modifying the circumscribing rectangle R (upper part of FIG. 8) of the first space portion 85a while maintaining the ratio of the sides so that the area of ​​the circumscribing rectangle R is the same as that of the cross section of the first space portion 85a (lower part of FIG. 8). Alternatively, the reference rectangle S3 (not shown) may be defined as a rectangle obtained by modifying the lengths of the sides of the circumscribing rectangle R so that the area of ​​the circumscribing rectangle R is the same as that of the cross section of the first space portion 85a and maximizes the overlap area with the cross section of the first space portion 85a. Note that the reference rectangle S3 may ultimately have 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 periphery is longer than at least one of the reference rectangles S1 to S3 defined in this manner, 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 of the above-described embodiment, 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 periphery is longer than any of the reference rectangles S1 to S3.

[0079] In the above-described embodiment, the first portion 86a and the second portion 86b of the first space portion 85a were both curved, but the cross-sectional shape of the first space portion 85a may be any of the above-described predetermined shapes (shapes whose outer periphery is longer than at least one of the reference rectangles S1 to S3), and various forms can be adopted for the cross-sectional shape of the first space portion 85a.

[0080] For example, one of the first portion 86a and the second portion 86b may be curved and the other linear. While the first portion 86a is generally curved, at least a portion of the first portion 86a may be curved, such as by combining a linear and a curved shape. The same applies to the second portion 86b. While both the first portion 86a and the second portion 86b are curved to be convex downward, at least one of them may be curved to be convex upward. While the first portion 86a and the second portion 86b are convex on the same vertical direction, this is not limiting and the embodiments shown in Figures 9 and 10 may also be employed. In Figure 9, the first portion 86a and the second portion 86b are convex on the sides that approach each other in the vertical direction. The second structural portion 88b in Figure 9 is thin at both ends in a cross section perpendicular to the front-to-rear direction and becomes thicker toward the horizontal center. As a result, the upper surface is curved to be convex upward, forming the second portion 86b of the first space portion 85a. In Fig. 10, the first portion 86a and the second portion 86b have convex shapes on the sides that are spaced apart from each other in the up-down direction. The first structural portion 88a and the fourth structural portion 88d in Fig. 10 are curved so that the lower surface as a whole has an upward convex shape, constituting the first portion 86a.

[0081] Furthermore, the first space 85a may be divided into a plurality of spaces. For example, as shown in FIG. 11, the first space 85a may be divided into two spaces, an upper space 85a1 and a lower space 85a2, by a fourth structural portion 88d. The fourth structural portion 88d extends over the entire front-rear direction of the first diffusion-controlling portion 11, and its left and right ends are connected to the second solid electrolyte layer 6. The fourth structural portion 88d is curved to have a constant thickness and a downwardly convex shape. The space 85a1 and the space 85a2 are each curved so that the first portion (upper side) and the second portion (lower side) are downwardly convex, similar to the first space 85a shown in FIG. 5. As a result, the cross-sectional shape of each of the space 85a1 and the space 85a2 perpendicular to the front-rear direction has the predetermined shape described above. For example, by forming three layers, two upper and lower vanishing material layers and a structural material layer between them, instead of vanishing material layer 185a in Fig. 7A, it is possible to produce space portion 85a1, space portion 85a2, and fourth structural portion 88d in Fig. 11. In Fig. 11, first space portion 85a is divided into two spaces, but it may be divided into three or more spaces.

[0082] Alternatively, as shown in Fig. 12, the first space 85a may be divided into four spaces 85a1-85a arranged in the left-right direction by fourth to sixth structural portions 88d-88f. The fourth to sixth structural portions 88d-88f each extend across the entire first diffusion-controlling section 11 in the front-rear direction, with their upper ends connected to the first structural portion 88a and their lower ends connected to the second structural portion 88b, the third structural portion 88c, or the spacer layer 5. Each of the spaces 85a1-85a4 has a first portion (upper side) and a second portion (lower side) curved to form a downwardly convex shape. As a result, each of the spaces 85a1-85a4 has a cross-sectional shape perpendicular to the front-rear direction that has the predetermined shape described above. For example, instead of the vanishing material layer 185a in Fig. 7A, four vanishing material layers and three structural material layers can be formed alternately in the left-right direction to produce the spaces 85a1-85a4 and the fourth to sixth structural portions 88d-88f in Fig. 12. In Fig. 12, the first space 85a is divided into four spaces, but it may be divided into two or three, or five or more.

[0083] In the above-described embodiment, at least a portion of the first portion 86a and / or at least a portion of the second portion 86b may be formed in a polygonal shape rather than a curved shape. For example, the embodiment shown in FIG. 13 may be adopted. In FIG. 13, the first portion 86a of the first space 85a is formed in a polygonal shape consisting of three straight lines and two bent portions, and is convex upward. The first portion 86a is formed by the first structural portion 88a, the fourth structural portion 88d, and the lower surface of the second solid electrolyte layer 6. The second portion 86b is formed by three straight lines and two bent portions, and is convex downward. The first space 85a has a cross section perpendicular to the front-rear direction that has a polygonal shape with five or more sides (here, an octagonal shape). The second portion 86b is formed by the second structural portion 88b, the third structural portion 88c, and the upper surface of the spacer layer 5. The first space portion 85a in Figure 13 has a first portion 86a and a second portion 86b in a cross section perpendicular to the front-to-rear direction that are polygonal, so that the cross-sectional shape is the above-mentioned specified shape (a shape whose outer periphery is longer than at least one of the reference rectangles S1 to S3).

[0084] In the above-described embodiment, the third portion 86c and the fourth portion 86d have a linear shape along the up-down direction in a cross section perpendicular to the front-rear direction. However, this is not limited to this. For example, the third portion 86c and the fourth portion 86d may have a curved shape as shown in FIG. 14. In FIG. 14, 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, and the first to third structural material layers 188a to 188c shown in FIG. 7A, the vanishing material layer 185a and the first to third structural material layers 188a to 188c can be deformed so as to bulge left and right during the pressure bonding process, thereby forming the first space portion 85a having the shapes of the third portion 86c and the fourth portion 86d shown in FIG. 14.

[0085] In the above-described embodiment, the boundaries between the first to fourth portions 86a to 86d are defined as corners, as shown in Fig. 5, but this is not limiting. For example, if the third portion 86c and the fourth portion 86b in Fig. 10 have curved shapes as shown in Fig. 14, the outer periphery of the cross section of the first space 85a may be close to an ellipse, as shown in Fig. 15, and the boundaries between the first to fourth portions 86a to 86d may not be clearly defined. In such a case, the outer periphery of the first space 85a, which is located in a region that is 90% of the length (=0.9W) of the center of the left and right sides of the first space 85a based on the left and right width W, as shown in Fig. 15, is defined as the first portion 86a and the second portion 86b. For example, even if the boundary between the first portion 86a and the second portion 86b and the rest of the outer periphery of the first spatial portion 85a is not clear, as shown in Figure 15, if the first portion 86a and the second portion 86b defined in this manner are curved, the first spatial portion 85a is considered to have curved first portion 86a and second portion 86b.

[0086] In the above-described embodiment, the first space 85a has the first to fourth portions 86a to 86d, but this is not limiting. For example, in Fig. 10, the first space 85a may not have the third portion 86c and the fourth portion 86d, and the outer periphery of the cross section 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 the left and right ends.

[0087] In the above-described embodiment, the first space 85a 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 the cross section of the first space 85a may have the predetermined shape described above at least in a portion in the front-rear direction. For example, only the front end (upstream end) of the first space 85a may have the cross section shown in FIG. 5 , and the cross section perpendicular to the front-rear direction at other portions may be rectangular. Furthermore, the first space 85a may be formed so that the cross-sectional area of ​​the cross section perpendicular to the front-rear direction is smaller at least in a portion downstream of the upstream end than at the upstream end. For example, the embodiment shown in FIG. 16 may be adopted. FIG. 16 shows a cross section of the first space 85a parallel to the front-rear direction. In FIG. 16, upper and lower contours 86e and 86f of the first space 85a parallel to the front-rear direction are both curved, and both contours 86e and 86f extend so as to curve relative to 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 first space 85a 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 a portion of the first space 85a where the 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 first space 85a also 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-controlling section 11. The shapes of the contours 86e and 86f of the first space 85a in FIG. 16 can be adjusted by the shapes of the first to third structural portions 88a to 88c, similar to the shapes of the first portion 86a and the second portion 86b. The first space 85a shown in FIG. 16 may have a predetermined shape in any cross section perpendicular to the front-rear direction. For example, the first space 85a may have a shape similar to that shown in FIG. 5 in any cross section in the front-rear direction.

[0088] The embodiment shown in FIG. 16 may be replaced with the embodiment shown in FIG. 17 or 18. In FIG. 17, the contour 86e has a curved shape formed by connecting two contours 86e of FIG. 16 in a front-to-back direction, and the contour 86f has a curved shape formed by connecting two contours 86f of FIG. 16 in a front-to-back direction. Therefore, the contours 86e and 86f of FIG. 17 have two convex shapes on sides that approach each other in the vertical direction. As a result, in FIG. 17, the first space 85a has two smallest cross-sectional areas in a cross section perpendicular to the front-to-back direction, located midway in the front-to-back direction (at positions other than the front and rear ends), resulting in high pressure loss of the measurement gas passing through these two locations. In FIG. 18, the upper and lower contours 86e and 86f of the first space 85a in a cross section parallel to the front-to-back direction are both curved, and both contours 86e and 86f extend so as to curve relative to the front-to-back direction. Furthermore, the contours 86e and 86f have convex shapes on the same side (the 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 first space 85a in FIG. 18 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 first space 85a in FIG. 18. The first space 85a shown in FIGS. 17 and 18 may have a predetermined shape in the cross section perpendicular to the front-rear direction at any portion in the front-rear direction. For example, the first space 85a in any cross section in the front-rear direction may have a shape similar to that shown in FIG. 5.

[0089] In the above-described embodiment, the first diffusion rate-controlling section 11 has a first space 85a provided between the spacer layer 5 and the second solid electrolyte layer 6 and a second space 85b provided between the spacer layer 5 and the second solid electrolyte layer 6. However, this is not limited thereto, and the first diffusion rate-controlling section 11 may have only one of the first space 85a and the second space 85b. Furthermore, the first space 85a of the first diffusion rate-controlling section 11 is a space provided between the adjacent spacer layer 5 and the second solid electrolyte layer 6. However, this is not limited thereto, and the first space 85a may be a space formed by punching out any of the layers constituting the element body 102. For example, the sensor element 101 may include a first diffusion rate-controlling section 211 having a space 285 shown in FIGS. 19 to 21. As shown in FIGS. 19 to 21, the space 285 of the first diffusion rate-controlling section 211 is formed as a space formed by punching out the spacer layer 5. The space 285 is longer in the up-down direction than the first space 85a, and therefore is configured so that the cross-sectional area perpendicular to the front-to-rear direction is approximately the same as that of the first space 85a by making the length in the left-to-right direction shorter than that of the first space 85a. Also, the left-to-right length of the space 285 is shorter than that of the buffer space 12 (see FIG. 20).

[0090] As shown in FIG. 21, in a 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 up-down direction, respectively. The first portion 286a and the second portion 286b have shapes similar to the first portion 86a and the second portion 86b in FIG. 5. Specifically, the first portion 286a and the second portion 286b are both curved and convex toward the same side in the vertical direction (here, the downward side). 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. 5. The cross section of the space 85 has a longer vertical length than a horizontal length. The shapes of the first portion 286a and the second portion 286b of the space 285 can be adjusted by the shapes of the first to third structural portions 288a to 288c of the structural portion 288, similar to the shapes of the first portion 86a and the second portion 86b. Specifically, the first structural portion 288a is disposed on the lower surface of the second solid electrolyte layer 6. The first structural portion 288a is thin at both ends in a cross section perpendicular to the front-rear direction and thickens toward the center, thereby forming a 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. The second structural portion 288b is thick at its left end in a cross section perpendicular to the front-rear direction and thins toward the center. The third structural portion 288c is thick at its right end in a cross section perpendicular to the front-rear direction and thins toward the center. As a result, the second structural portion 288b and the third structural portion 288c as a whole are curved so that their upper surfaces are convex downward, forming a second portion 286b. Note that the structural portion 288 is not shown in FIG. 19.The linear third portion 286c and fourth portion 286d are not part of the structural portion 288 but are formed as the inner circumferential surface (side surface) of a punched hole (a hole vertically penetrating the spacer layer 5) provided in the spacer layer 5. As in the first diffusion-controlling portion 11 of the above-described embodiment, the first portion 286a and the second portion 286b of the space 285 in a cross section perpendicular to the front-rear direction are curved, so that the cross-sectional shape of the space 285 has the predetermined shape described above (a shape whose outer periphery is longer than at least one of the reference rectangles S1 to S3). This reduces the hydraulic diameter of the space 285 compared to at least one of the reference rectangles S1 to S3, thereby increasing the pressure loss of the measurement gas passing through the space 285. Therefore, the same effect as that of the first space 85a of the above-described embodiment can be achieved. The shape of the space 285 may be any of the various aspects of the first space 85a described above.

[0091] In the above-described embodiment, the cross-sectional shapes of the first spatial portion 85a and the second spatial portion 85b of the first diffusion rate-controlling portion 11 are predetermined shapes, but this is not limited to this, and the cross-sectional shapes of one or more of the first diffusion rate-controlling portion 11, the second diffusion rate-controlling portion 13, the third diffusion rate-controlling portion 30, and the fourth diffusion rate-controlling portion 60 may be predetermined shapes.

[0092] 19, the front end of the first diffusion-controlling portion 11, 211 is the gas inlet 10, but this is not limiting. For example, the first bridging portion 5a and the first diffusion-controlling portion 11 may be disposed rearward of the gas inlet 10 in the measurement gas flow portion.

[0093] In the above-described embodiment, the first space 85a, the second space 85b, and the space 285 allow the measurement gas to flow in the front-to-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 measurement gas may flow in the left-to-right direction through the first space 85a. In this case, the left-to-right direction corresponds to the first direction, and the front-to-rear direction corresponds to the second direction.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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]

[0098] 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]

[0099] 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, 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-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 to 85a4 space portions, 86a to 86d first to fourth portions, 86e, 86f contour, 88 structural portion, 88a to 88f first to sixth 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 crosslinking part, 185a vanishing material layer, 188a~188c first to third structural material layer, 211 first diffusion controlling part, 285 space part, 286a~286d first part to fourth part, 288 structural part, 288a~288c first to third structural part, R Circumscribed rectangle, S1~S2 reference rectangle.

Claims

1. A sensor element for detecting the concentration of a specific gas in a measurement gas, an element body having a longitudinal direction, the element body being a laminate formed by laminating a plurality of layers including an oxygen ion conductive solid electrolyte layer in a lamination direction perpendicular to the longitudinal direction, the element body having a measurement gas flow section therein that introduces the measurement gas from a gas inlet and flows the measurement gas in a first direction; a pump cell including 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 has a space portion through which the measurement gas flows in the first direction, a cross section of the space perpendicular to the first direction in at least a part of the first direction has a predetermined shape whose perimeter is 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 each side, or a rectangle obtained by changing the length of each side so that the overlapping area with the cross section is maximized. Sensor element.

2. 2. The sensor element according to claim 1, 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 at least a portion of the second portion are curved. Sensor element.

3. 3. The sensor element according to claim 1, 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.

4. 3. The sensor element according to claim 2, the first portion and the second portion have a convex shape on the same side in the stacking direction; Sensor element.

5. 3. The sensor element according to claim 2, 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.

6. 3. The sensor element according to claim 1, The cross section of the space has a length in the second direction that is greater than a length in the stacking direction. Sensor element.

7. 3. The sensor element according to claim 1, 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.

8. 3. The sensor element according to claim 1, The space portion is formed such that a cross-sectional area of ​​the space 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.

9. 9. The sensor element according to claim 8, The space portion extends such that a cross-sectional outline parallel to the first direction is curved with respect to the first direction. Sensor element.

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

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