JP6684615B2 - Sensor element and gas sensor - Google Patents

Description

  The present invention relates to a sensor element and a gas sensor.

  Conventionally, there is known a gas sensor including a sensor element that detects a concentration of a predetermined gas such as NOx in a measured gas such as an exhaust gas of an automobile. In such a gas sensor, it is known to form a protective layer on the surface of the sensor element. For example, Patent Documents 1 and 2 describe forming a protective layer on the surface of a sensor element by printing or plasma spraying. By forming this protective layer, cracking of the sensor element due to adhesion of moisture in the gas under measurement can be suppressed, for example.

JP2011-214853A Patent No. 3766572

  The sensor element of such a gas sensor has a high temperature during normal driving (for example, 800 ° C.), and it has been desired to further suppress cracking of the sensor element due to rapid cooling due to adhesion of moisture.

  The present invention has been made to solve such a problem, and its main purpose is to improve the water resistance of the element body of the sensor element.

  The present invention adopts the following means in order to achieve the above-mentioned main object.

The sensor element of the present invention is
A long rectangular parallelepiped-shaped element body provided with an oxygen ion conductive solid electrolyte layer,
An outer electrode disposed on the first surface, which is one of the surfaces of the element body,
A protective layer which covers at least a part of a second surface of the element body opposite to the first surface, and which has one or more exposed spaces where the second surface is exposed;
It is equipped with.

  In this sensor element, the protective layer covers at least a part of the second surface of the surface of the element body opposite to the first surface on which the outer electrode is arranged. Then, the protective layer has one or more exposed spaces in which the second surface is exposed. Thereby, the heat conduction in the thickness direction of the protective layer can be insulated by the exposed space, so that the cooling of the element body when water adheres to the surface of the protective layer is suppressed. Therefore, the water resistance of the element body is improved.

  In the sensor element of the present invention, at least one of the exposed spaces is arranged so as to overlap with a center of a region of the second surface covered with the protective layer when viewed from a direction perpendicular to the second surface. It may be located. Here, the center of the area covered with the protective layer is likely to have a relatively high temperature, and the portion far from the center (for example, a portion near the end of the second surface) is relatively unlikely to have a high temperature. Therefore, by insulating the center of the region of the second surface covered by the protective layer with the exposed space, the water resistance of the element body is further improved. The "center of the area of the second surface covered by the protective layer" may be the center of the second surface of the area covered by the protective layer in the lateral direction. Of the second surface may be the center of the second surface in the lateral direction and the center of the second surface in the longitudinal direction (that is, the center of the region covered with the protective layer).

  In the sensor element of the present invention, at least one of the exposed spaces may have an opening that communicates with the outside of the protective layer. In this way, the heat in the exposed space can be released from the opening, so that overheating of the element body is suppressed. Therefore, it is possible to suppress a rapid temperature decrease of the element body when water adheres to the surface of the protective layer, and the water resistance of the element body is improved.

  In the sensor element of the present invention, the protective layer is positioned so as to be displaced in a direction perpendicular to the second surface with respect to the plurality of exposed spaces and at least one of the plurality of exposed spaces, and the second surface is exposed. And a plurality of non-exposed spaces that do not exist. When there are a plurality of such spaces in the protective layer, the strength of the protective layer is less likely to decrease than in the case where there is one space with the same total volume. Therefore, by providing a space in the protective layer, it is possible to improve the water resistance and prevent a decrease in the strength of the protective layer due to the presence of the space.

  In the sensor element of the present invention, the protective layer may have, for at least one of the exposed spaces, one or more columnar portions that support the exposed space in a direction perpendicular to the second surface. In this case, the columnar portion supports the exposed space, so that the reduction in strength of the protective layer can be suppressed.

  In the sensor element of the aspect of the invention having a columnar portion, the protective layer has a plurality of the columnar portions, and the plurality of the columnar portions, when viewed from a direction perpendicular to the second surface, The columnar portions may be arranged such that the density of the columnar portions increases as the distance from the center of the region covered by the protective layer on the second surface increases. Here, the center of the area covered with the protective layer is likely to have a relatively high temperature, and the portion far from the center (for example, a portion near the end of the second surface) is relatively unlikely to have a high temperature. Therefore, by making the density of the columnar portion higher in the portion where the temperature is relatively less likely to become high, the columnar portion suppresses the decrease in the strength of the protective layer, and the columnar portion exists in the region where the temperature tends to become high. It is possible to suppress a decrease in the heat insulating effect of the exposed space due to. Therefore, it is possible to further improve the water resistance of the element body while further suppressing the decrease in the strength of the protective layer. Here, "the tendency that the density of the columnar parts becomes high" includes the tendency that the number of the columnar parts per unit area becomes large and the thickness of the columnar parts becomes thick.

  In the sensor element of the aspect of the present invention having a columnar portion, the plurality of columnar portions have a center of a region of the second surface covered with the protective layer when viewed from a direction perpendicular to the second surface. The columnar portions may be arranged so that the closer they are, the higher the density of the columnar portions becomes.

  In the sensor element of the present invention, the protective layer may have a plurality of the exposed spaces whose longitudinal direction is along the longitudinal direction of the second surface, along the lateral direction of the second surface. Since there are a plurality of elongated exposed spaces along the longitudinal direction of the second surface along the lateral direction of the second surface, the protective layer is caused by the difference in thermal expansion coefficient between the protective layer and the element body when exposed to water. Therefore, the stress on the element body along the lateral direction of the second surface is reduced. Therefore, the element body is less likely to break when exposed to water, and the water resistance of the element body is further improved. In this case, the exposed space whose longitudinal direction is along the longitudinal direction of the second surface may be a rectangular parallelepiped space in which one side along the lateral direction of the second surface is shorter than the other two sides. .

  In the sensor element of the present invention, the protective layer may have a plurality of the exposed spaces whose longitudinal direction is along the lateral direction of the second surface, along the longitudinal direction of the second surface. Since there are a plurality of elongated exposed spaces along the lateral direction of the second surface along the longitudinal direction of the second surface, the protective layer is caused by the difference in thermal expansion coefficient between the protective layer and the element body when exposed to water. Therefore, the stress on the element body along the longitudinal direction of the second surface is reduced. Therefore, the element body is less likely to break when exposed to water, and the water resistance of the element body is further improved. In this case, the exposed space whose longitudinal direction is along the lateral direction of the second surface may be a rectangular parallelepiped space in which one side along the longitudinal direction of the second surface is shorter than the other two sides. .

  In the sensor element of the present invention, the protective layer has a plurality of first exposed spaces whose longitudinal direction is the exposed space along the longitudinal direction of the second surface, along the lateral direction of the second surface. And a plurality of second exposed spaces, which are the exposed spaces whose longitudinal direction extends along the lateral direction of the second surface and intersect the first exposed space, along the longitudinal direction of the second surface. You may have. By doing so, both the stress along the lateral direction and the stress along the longitudinal direction of the second surface from the protective layer to the element body due to the difference in thermal expansion coefficient between the protective layer and the element body when exposed to water are both generated. Will be reduced. Therefore, the element body is less likely to break when exposed to water, and the water resistance of the element body is further improved.

  In the sensor element of the present invention, at least one of the exposed spaces may have a shape such that the exposed space becomes narrower as the distance from the second surface increases. The exposed space having such a shape can suppress a decrease in strength of the protective layer, as compared with, for example, a rectangular parallelepiped space having an inner surface parallel to the second surface.

  In the sensor element of the present invention, at least one of the exposed spaces may have at least two inner surfaces inclined in a direction in which the exposed spaces are closer to each other as the distance from the second surface increases. The exposed space having such an inner surface can suppress the decrease in strength of the protective layer as compared with, for example, a rectangular parallelepiped space having an inner surface parallel to the second surface.

  In the sensor element of the present invention, at least one of the exposed spaces may have a curved surface in which an inner surface facing the second surface is curved outward. The exposed space having such an inner surface can suppress the decrease in strength of the protective layer as compared with, for example, a rectangular parallelepiped space having an inner surface parallel to the second surface.

The gas sensor of the present invention is
The sensor element according to any one of the aspects described above is provided.

  This gas sensor includes the sensor element according to any one of the above-described aspects of the present invention. Therefore, an effect similar to that of the sensor element of the present invention described above, for example, an effect of improving water resistance of the element body is obtained.

The perspective view which showed roughly an example of the structure of the sensor element 101 of 1st Embodiment. The sectional view showing roughly an example of the composition of gas sensor 100 of a 1st embodiment. 1. BB sectional drawing of FIG. CC sectional drawing of FIG. FIG. 4 is a sectional view taken along line DD of FIG. 3. Sectional drawing of 101 A of sensor elements of 2nd Embodiment. EE sectional drawing of FIG. Sectional drawing of the sensor element 101B of 3rd Embodiment. F-F sectional drawing of FIG. Sectional drawing of 101 C of sensor elements of 4th Embodiment. FIG. 11 is a sectional view taken along line GG of FIG. 10. Sectional drawing of the sensor element 101D of 5th Embodiment. The HH sectional view of FIG. Sectional drawing of the sensor element 101E of 6th Embodiment. FIG. 15 is a sectional view taken along line I-I of FIG. 14. Sectional drawing of the sensor element 101F of 7th Embodiment. FIG. 17 is a sectional view taken along line JJ of FIG. 16. FIG. 17 is a sectional view taken along line KK of FIG. 16. Sectional drawing of the sensor element 101G of 8th Embodiment. FIG. 20 is a sectional view taken along line LL in FIG. 19. Sectional drawing of the sensor element 101H of 9th Embodiment. FIG. 22 is a sectional view taken along line MM in FIG. 21. Sectional drawing of the sensor element 101I of 10th Embodiment. The bottom view of the front end periphery of sensor element 101I. Sectional drawing of the sensor element 101J of 11th Embodiment. The bottom view of the front end periphery of sensor element 101J. Sectional drawing of the sensor element 101K of 12th Embodiment. The bottom view of the front end periphery of sensor element 101K.

[First Embodiment]
Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view schematically showing an example of the configuration of a sensor element 101 included in the gas sensor 100 according to the first embodiment. FIG. 2 is a sectional view schematically showing an example of the configuration of the gas sensor 100. The cross-sectional portion of the sensor element 101 in FIG. 2 is the AA cross section in FIG. FIG. 3 is a sectional view taken along line BB of FIG. In FIG. 3, illustration of the inside of the cross section of the element body 102 is omitted. FIG. 4 is a sectional view taken along line CC of FIG. FIG. 5 is a cross-sectional view taken along the line DD of FIG. The sensor element 101 has a long rectangular parallelepiped shape, and the longitudinal direction of the sensor element 101 (left-right direction in FIG. 2) is the front-back direction, and the thickness direction of the sensor element 101 (up-down direction in FIG. 2) is the up-down direction. To do. Further, the width direction of the sensor element 101 (the direction perpendicular to the front-back direction and the vertical direction) is defined as the left-right direction.

The gas sensor 100 is attached to, for example, a pipe such as an exhaust gas pipe of a vehicle, and is used to measure the concentration of a specific gas such as NOx or O ₂ contained in the exhaust gas as the gas to be measured. In the present embodiment, the gas sensor 100 measures the NOx concentration as the specific gas concentration. The gas sensor 100 includes a sensor element 101. The sensor element 101 includes a sensor element body 102 and a porous protective layer 84 that covers the sensor element body 102. The sensor element body 102 refers to a portion of the sensor element 101 other than the protective layer 84.

As shown in FIG. 2, the sensor element 101 includes a first substrate layer 1, a second substrate layer 2, and a third substrate layer 3, each of which is an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO ₂ ). The first solid electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6 are six layers stacked in this order from the bottom in the drawing. The solid electrolyte forming these six layers is dense and airtight. The sensor element 101 is manufactured by, for example, performing predetermined processing and printing a circuit pattern on a ceramic green sheet corresponding to each layer, stacking them, and then firing and integrating them.

  The gas introduction port 10 and the first diffusion portion are provided between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, which is one end portion (front end portion) of the sensor element 101. In a mode in which the rate-controlling part 11, the buffer space 12, the second diffusion-controlling part 13, the first internal space 20, the third diffusion-controlling part 30, and the second internal space 40 communicate with each other in this order. Adjacent to each other.

  The gas inlet 10, the buffer space 12, the first internal space 20, and the second internal space 40 are provided on the lower surface of the second solid electrolyte layer 6 with the upper portion provided in a mode in which the spacer layer 5 is hollowed out. The lower part is the upper surface of the first solid electrolyte layer 4, and the side part is the space defined by the side surface of the spacer layer 5 inside the sensor element 101.

  The first diffusion control part 11, the second diffusion control part 13, and the third diffusion control part 30 are all provided as two horizontally long slits (the opening has a longitudinal direction in a direction perpendicular to the drawing). . The portion from the gas inlet 10 to the second inner space 40 is also referred to as a gas distribution portion.

  Further, at a position farther from the front end side than the gas flow section, between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5, the side portion is partitioned by the side surface of the first solid electrolyte layer 4. A reference gas introduction space 43 is provided at the position. For example, the atmosphere is introduced into the reference gas introduction space 43 as a reference gas when the NOx concentration is measured.

  The atmosphere introduction layer 48 is a layer made of porous ceramics, and the reference gas is introduced into the atmosphere introduction layer 48 through the reference gas introduction space 43. The atmosphere introduction layer 48 is formed so as to cover the reference electrode 42.

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

  In the gas flow section, the gas introduction port 10 is a portion opened to the external space, and the gas to be measured is taken into the sensor element 101 from the external space through the gas introduction port 10. The first diffusion control part 11 is a part that imparts a predetermined diffusion resistance to the gas to be measured taken in from the gas inlet 10. The buffer space 12 is a space provided for guiding the gas to be measured introduced from the first diffusion control section 11 to the second diffusion control section 13. The second diffusion control part 13 is a part that imparts a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal space 20. When the gas to be measured is introduced from the outside of the sensor element 101 into the first internal space 20, the pressure fluctuation of the gas to be measured in the external space (if the gas to be measured is exhaust gas of an automobile, pulsation of exhaust pressure). The gas to be measured which is rapidly taken into the inside of the sensor element 101 from the gas introduction port 10 is not directly introduced into the first internal space 20, but the first diffusion control part 11, the buffer space 12, the second space. After the variation of the concentration of the gas to be measured is canceled through the diffusion rate controlling unit 13, the gas is introduced into the first internal space 20. As a result, the concentration fluctuation of the measured gas introduced into the first internal void 20 becomes almost negligible. The first internal space 20 is provided as a space for adjusting the partial pressure of oxygen in the gas to be measured introduced through the second diffusion control section 13. The oxygen partial pressure is adjusted by operating the main pump cell 21.

  The main pump cell 21 includes an inner pump electrode 22 having a ceiling electrode portion 22 a provided on almost the entire lower surface of the second solid electrolyte layer 6 facing the first inner space 20, and an upper pump electrode 22 of the upper surface of the second solid electrolyte layer 6. An electrochemical pump cell composed of an outer pump electrode 23 provided in a region corresponding to the ceiling electrode portion 22a so as to be exposed to the external space, and a second solid electrolyte layer 6 sandwiched between these electrodes. is there.

  The inner pump electrode 22 is formed so as to extend over the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that partition the first inner space 20, and the spacer layer 5 that provides the side wall. There is. 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 void 20, and a bottom portion is provided on the upper surface of the first solid electrolyte layer 4 that provides the bottom surface. A spacer layer in which the electrode portions 22b are formed, and the side electrode portions (not shown) 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. 5 is formed on the side wall surface (inner surface) of the side electrode portion 5 and is arranged in a tunnel-shaped structure at the side electrode portion.

The inner pump electrode 22 and the outer pump electrode 23 are formed as porous cermet electrodes (for example, cermet electrodes of Pt containing 1% Au and ZrO ₂ ). The inner pump electrode 22 that comes into contact with the gas to be measured is formed using a material having a reduced ability to reduce NOx components in the gas to be measured.

  In the main pump cell 21, a desired pump voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23 so that a pump current flows between the inner pump electrode 22 and the outer pump electrode 23 in the positive direction or the negative direction. By flowing Ip0, it is possible to pump oxygen in the first internal space 20 into the external space or pump oxygen in the external space into the first internal space 20.

  In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere in the first internal space 20, the inner pump electrode 22, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4 The third substrate layer 3 and the reference electrode 42 form an electrochemical sensor cell, that is, an oxygen partial pressure detection sensor cell 80 for controlling the main pump.

  By measuring the electromotive force V0 in the main pump control oxygen partial pressure detection sensor cell 80, the oxygen concentration (oxygen partial pressure) in the first internal space 20 can be known. Further, the pump current Ip0 is controlled by feedback controlling the pump voltage Vp0 of the variable power supply 25 so that the electromotive force V0 becomes constant. Thereby, the oxygen concentration in the first inner space 20 can be maintained at a predetermined constant value.

  The third diffusion control part 30 imparts a predetermined diffusion resistance to the measured gas whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 21 in the first internal space 20, and supplies the measured gas to the measured gas. This is a part that leads to the second internal space 40.

  The second internal space 40 is provided as a space for performing a process related to the measurement of the nitrogen oxide (NOx) concentration in the measured gas introduced through the third diffusion control part 30. In the measurement of the NOx concentration, the NOx concentration is mainly measured by the operation of the measurement pump cell 41 in the second internal space 40 where the oxygen concentration is adjusted by the auxiliary pump cell 50.

  In the second internal void 40, after the oxygen concentration (oxygen partial pressure) in the first internal void 20 is adjusted in advance, the auxiliary pump cell 50 is further added to the gas to be measured introduced through the third diffusion control section 30. The oxygen partial pressure is adjusted by. As a result, the oxygen concentration in the second inner space 40 can be kept constant with high precision, and thus the gas sensor 100 can accurately measure the NOx concentration.

  The auxiliary pump cell 50 includes 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 (the outer pump electrode 23). However, the auxiliary electrochemical pump cell is composed of a second solid electrolyte layer 6 and a suitable electrode outside the sensor element 101).

  The auxiliary pump electrode 51 is arranged in the second internal space 40 in the same tunnel structure as the inner pump electrode 22 provided in the first internal space 20. That is, the ceiling electrode portion 51a is formed for the second solid electrolyte layer 6 that provides the ceiling surface of the second internal void 40, and the first solid electrolyte layer 4 that provides the bottom surface of the second internal void 40 is provided. , The bottom electrode portion 51b is formed, and the side electrode portion (not shown) that connects the ceiling electrode portion 51a and the bottom electrode portion 51b to each other forms the side wall of the second inner space 40. It has a tunnel-like structure formed on both wall surfaces. The auxiliary pump electrode 51 is also made of a material having a reduced ability to reduce NOx components in the gas to be measured, like the inner pump electrode 22.

  In the auxiliary pump cell 50, by applying a desired voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23, oxygen in the atmosphere in the second internal space 40 is pumped to the external space or externally. It is possible to pump into the second internal space 40 from the space.

  Further, in order to control the oxygen partial pressure in the atmosphere in the second internal space 40, the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte. The layer 4 and the third substrate layer 3 constitute an electrochemical sensor cell, that is, an oxygen partial pressure detection sensor cell 81 for controlling the auxiliary pump.

  The auxiliary pump cell 50 performs pumping by the variable power source 52 whose voltage is controlled based on the electromotive force V1 detected by the auxiliary pump control oxygen partial pressure detection sensor cell 81. As a result, the oxygen partial pressure in the atmosphere inside the second internal space 40 is controlled to a low partial pressure that does not substantially affect the measurement of NOx.

  At the same time, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor cell 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor cell 80 for main pump control, and the electromotive force V0 thereof is controlled, so that the third diffusion-controlling section 30 causes the second internal void space. The gradient of the oxygen partial pressure in the gas to be measured introduced into 40 is controlled so as to be always constant. When used as a NOx sensor, the oxygen concentration in the second internal space 40 is maintained at a constant value of about 0.001 ppm by the action of the main pump cell 21 and the auxiliary pump cell 50.

  The measurement pump cell 41 measures the NOx concentration in the measured gas in the second internal space 40. The measurement pump cell 41 includes a measurement electrode 44, which is provided on the upper surface of the first solid electrolyte layer 4 facing the second internal space 40 and apart from the third diffusion control part 30, and an outer pump electrode 23. , The second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4 are electrochemical pump cells.

  The measurement electrode 44 is a porous cermet electrode. The measurement electrode 44 also functions as a NOx reduction catalyst that reduces NOx existing in the atmosphere inside the second internal space 40. Further, the measurement electrode 44 is covered with the fourth diffusion control part 45.

  The fourth diffusion control part 45 is a film made of a ceramic porous body. The fourth diffusion control part 45 plays a role of limiting the amount of NOx flowing into the measurement electrode 44, and also functions as a protective film of the measurement electrode 44. In the measurement pump cell 41, oxygen generated by the decomposition of nitrogen oxide in the atmosphere around the measurement electrode 44 can be pumped out, and the generated amount can be detected as the pump current Ip2.

  Further, in order to detect the oxygen partial pressure around the measurement electrode 44, an electrochemical sensor cell, that is, the first solid electrolyte layer 4, the third substrate layer 3, the measurement electrode 44, and the reference electrode 42, that is, An oxygen partial pressure detection sensor cell 82 for measuring pump control is configured. The variable power supply 46 is controlled based on the electromotive force V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82.

The gas to be measured introduced into the second internal space 40 reaches the measurement electrode 44 through the fourth diffusion control part 45 under the condition that the oxygen partial pressure is controlled. Nitrogen oxide in the measured gas around the measuring electrode 44 is reduced (2NO → N ₂ + O ₂ ) to generate oxygen. Then, the generated oxygen is pumped by the measuring pump cell 41. At this time, the variable power source is used so that the electromotive force V2 detected by the measuring pump controlling oxygen partial pressure detecting sensor cell 82 becomes constant. The voltage Vp2 of 46 is controlled. Since the amount of oxygen generated around the measurement electrode 44 is proportional to the concentration of nitrogen oxide in the measurement gas, the pump current Ip2 in the measurement pump cell 41 is used to measure the nitrogen oxide in the measurement gas. The concentration will be calculated.

  If the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42 are combined to constitute the oxygen partial pressure detecting means as an electrochemical sensor cell, the measuring electrode 44 The electromotive force corresponding to the difference between the amount of oxygen generated by the reduction of NOx components in the surrounding atmosphere and the amount of oxygen contained in the reference atmosphere can be detected, and the concentration of NOx components in the measured gas can be detected. It is also possible to ask

  An electrochemical sensor cell 83 is composed of the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42. The oxygen partial pressure in the gas to be measured outside the sensor can be detected by the electromotive force Vref obtained by the sensor cell 83.

  In the gas sensor 100 having such a configuration, by operating the main pump cell 21 and the auxiliary pump cell 50, the oxygen partial pressure is always kept at a constant low value (a value that does not substantially affect the measurement of NOx). The gas to be measured is supplied to the measurement pump cell 41. Therefore, the NOx concentration in the measured gas is determined based on the pump current Ip2 flowing when oxygen generated by the reduction of NOx is pumped out from the measurement pump cell 41 in substantially proportion to the NOx concentration in the measured gas. You can know it.

  Further, the sensor element 101 includes a heater unit 70 that plays a role of temperature adjustment for heating and keeping the temperature of the sensor element 101 in order to enhance the oxygen ion conductivity of the solid electrolyte. 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 diffusion hole 75.

  The heater connector electrode 71 is an electrode formed so as to be in contact with the lower surface of the first substrate layer 1. By connecting the heater connector electrode 71 to an external power source, power can be supplied to the heater unit 70 from the outside.

  The heater 72 is an electric resistor formed in such a manner that it is sandwiched between the second substrate layer 2 and the third substrate layer 3 from above and below. The heater 72 is connected to the heater connector electrode 71 through the through hole 73 and generates heat by being supplied with electric power from the outside through the heater connector electrode 71 to heat and keep the solid electrolyte forming the sensor element 101. .

  Further, the heater 72 is buried over the entire area from the first internal space 20 to the second internal space 40, and it becomes possible to adjust the temperature of the entire sensor element 101 to a temperature at which the solid electrolyte is activated. ing.

  The heater insulating layer 74 is an insulating layer formed of an insulator such as alumina 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 electrical insulation between the third substrate layer 3 and the heater 72.

  The pressure diffusion hole 75 is a portion that is provided so as to penetrate the third substrate layer 3 and communicate with the reference gas introduction space 43, and for the purpose of alleviating an increase in internal pressure due to a temperature increase in the heater insulating layer 74. Formed.

  The element body 102 is partially covered with a protective layer 84, as shown in FIGS. Here, since the sensor element 101 is a rectangular parallelepiped, as shown in FIGS. 1 to 3, as the outer surface of the solid electrolyte layer of the sensor element 101, the first surface 102a (upper surface), the second surface 102b (lower surface), It has six surfaces, that is, a third surface 102c (left side surface), a fourth surface 102d (right side surface), a fifth surface 102e (front end surface), and a sixth surface 102f (rear end surface). The protective layer 84 is a porous body and is formed on each of five surfaces (first to fifth surfaces 102a to 102e) of the six surfaces (first to sixth surfaces 102a to 102f) of the element body 102. The first to fifth protective layers 84a to 84e are provided. The first to fifth protective layers 84a to 84e are collectively referred to as the protective layer 84. Each of the first to fourth protective layers 84a to 84d covers an area up to a distance L (see FIG. 2) from the front end surface of the element body 102 toward the rear, on the surface of the element body 102 on which the element is formed. It covers everything. The first protective layer 84a also covers the portion of the first surface 102a where the outer pump electrode 23 is formed (see FIGS. 2 and 3). The fifth protective layer 84e also covers the gas inlet 10, but since the fifth protective layer 84e is a porous body, the gas to be measured can flow through the inside of the protective layer 84e and reach the gas inlet. is there. The protective layer 84 covers a part of the element body 102 (a part including the front end surface of the element body 102 from the front end surface to the distance L) to protect the part. The protective layer 84 plays a role of suppressing the generation of cracks in the element body 102 due to, for example, water in the gas to be measured adhere. It should be noted that the distance L is (0 <distance L <length in the longitudinal direction of the element body 102) based on the range in which the element body 102 is exposed to the gas to be measured in the gas sensor 100, the position of the outer pump electrode 23, and the like. It is defined by the range.

  In this embodiment, as shown in FIG. 1, the element body 102 has different lengths in the front-rear direction, widths in the left-right direction, and thicknesses in the up-down direction, and length> width> thickness. There is. Further, the distance L is set to be a value larger than the width and thickness of the element body 102.

  As shown in FIGS. 2 to 5, the protective layer 84 has a space 90 inside. Specifically, the first protective layer 84a has the upper space 91, the second protective layer 84b has the lower space 92, the third protective layer 84c has the left space 93, and the fourth protective layer 84d. Has a right side space 94. The spaces 91 to 94 are collectively referred to as a space 90.

  The upper space 91 is an exposed space where the first surface 102a is exposed, and is formed in a substantially rectangular parallelepiped shape. As shown in FIG. 4, the upper space 91 is a region of the first surface 102a covered by the protective layer 84 (first protective layer 84a) when viewed from a direction perpendicular to the first surface 102a, that is, in a top view. It is located so as to include the center of (a region from the front end face to the distance L of the first surface 102a). That is, the center of the region of the first surface 102 a covered by the protective layer 84 (first protective layer 84 a) is exposed in the upper space 91. The center of the region of the first surface 102a covered by the protective layer 84 means the center in the front-rear direction and the center in the left-right direction of the region. Further, the upper space 91 may be positioned such that at least a part of the upper space 91 overlaps with at least a part of the outer pump electrode 23 when viewed from above. In the present embodiment, as shown in FIG. 4, the upper space 91 is positioned so as to overlap the entire outer pump electrode 23 (the upper space 91 includes the entire outer pump electrode 23) when viewed from above. That is, the entire outer pump electrode 23 is exposed in the upper space 91.

  Unlike the upper space 91, the lower space 92, the left space 93, and the right space 94 have the second surface 102b, the third surface 102c, and the fourth surface 102d exposed, but have the same shape as the upper space 91. is doing. The positional relationship of the lower space 92, the left space 93, and the right space 94 with respect to the second surface 102b, the third surface 102c, and the fourth surface 102d is similar to the positional relationship of the upper space 91 with respect to the first surface 102a. The upper space 91 and the lower space 92 have vertically symmetrical shapes and arrangements. The left space 93 and the right space 94 have a symmetrical shape and arrangement.

  Specifically, the lower space 92 is an exposed space in which the second surface 102b is exposed, and is formed in a substantially rectangular parallelepiped shape. As shown in FIG. 5, the lower space 92 is a region of the second surface 102b covered by the protective layer 84 (second protective layer 84b) when viewed in a direction perpendicular to the second surface 102b, that is, when viewed from below. It is located so as to include the center of (the region from the front end face to the distance L of the second surface 102b). That is, the center of the region of the second surface 102b covered by the protective layer 84 (second protective layer 84b) is exposed in the lower space 92. The center of the region of the second surface 102b covered by the protective layer 84 means the center in the front-rear direction and the center in the left-right direction of the region.

  The third surface 102c of the left space 93 is exposed, and when viewed from a direction perpendicular to the third surface 102c, that is, from the left side, the left space 93 is covered with the protective layer 84 (third protective layer 84c) of the third surface 102c. It is located so as to include the center of the region (the region from the front end face to the distance L of the third surface 102c). In the right space 94, the fourth surface 102d is exposed, and when viewed from a direction perpendicular to the fourth surface 102d, that is, from the right side, the protective layer 84 (fourth protective layer 84d) of the fourth surface 102d is covered. It is located so as to include the center of the region (the region from the front end face to the distance L of the fourth surface 102d).

  The protective layer 84 is made of a porous body such as an alumina porous body, a zirconia porous body, a spinel porous body, a cordierite porous body, a titania porous body, or a magnesia porous body. In this embodiment, the protective layer 84 is made of an alumina porous body. Although not particularly limited, the thickness of the protective layer 84 is, for example, 100 to 1000 μm, and the porosity of the protective layer 84 is, for example, 5% by volume to 85% by volume.

  A method of manufacturing the gas sensor 100 thus configured will be described below. In the method of manufacturing the gas sensor 100, the element body 102 is manufactured first, and then the protective layer 84 is formed on the element body 102 to manufacture the sensor element 101.

  A method of manufacturing the element body 102 will be described. First, six unfired ceramic green sheets are prepared. Then, each of the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6 is respectively provided. Patterns such as electrodes, insulating layers, and resistance heating elements are printed on the ceramic green sheet. After forming various patterns in this way, the green sheet is dried. Then, they are laminated to form a laminated body. The laminate thus obtained includes a plurality of element bodies 102. The laminated body is cut into pieces of the size of the element body 102, and the element body 102 is obtained by firing at a predetermined firing temperature.

  Next, a method of forming the protective layer 84 on the element body 102 will be described. The protective layer 84 can be formed by various methods such as gel casting, screen printing, dipping, and plasma spraying. The space 90 in the protective layer 84 can be formed by using a vanishing material (for example, carbon or theobromine) that vanishes by combustion.

  The gel casting method is a method in which the slurry is solidified by a chemical reaction of the slurry itself to form a molded body. For example, a part of the element body 102 (a portion to be covered) is exposed inside the molding die, and the slurry is poured into a gap between the molding die and the element body 102 to be solidified. As the slurry used in the gel casting method, for example, a slurry containing raw material powder (ceramic particles or the like) for the protective layer 84, a sintering aid, an organic solvent, a dispersant and a gelling agent can be used. The gelling agent is not particularly limited as long as it contains at least two types of polymerizable organic compounds, and examples thereof include those containing two types of organic compounds capable of urethane reaction. Examples of such two types of organic compounds include isocyanates and polyols. In preparing a slurry, first, a raw material powder, a sintering aid, an organic solvent and a dispersant are added at a predetermined ratio and mixed for a predetermined time to prepare a slurry precursor. Immediately before using the slurry, a gelling agent is added to and mixed with the slurry precursor to form a slurry. It should be noted that any one or two of the isocyanates, the polyols and the catalyst constituting the gelling agent are added to the slurry precursor, and then the remaining components may be added when the slurry is prepared. Good. Since the chemical reaction (urethane reaction) of the gelling agent begins to proceed with time, the slurry after the gelling agent is added to the slurry precursor is preferably poured into the molding die promptly.

  For example, when forming the protective layer 84, it is performed as follows. First, a vanishing material is applied to the surface of the element body 102 and dried to form vanishing bodies in the shapes of the upper space 91, the lower space 92, the left space 93, and the right space 94. The disappearance material can be applied by screen printing, gravure printing, inkjet printing, or the like. Further, the extinguishing body may be formed by repeating coating and drying a plurality of times. Next, the protective layer 84 is formed on the surface of the element body 102. As a result, the protective layer 84 including the disappearing body in the shape of the space 90 is formed. After that, the extinguishing body is extinguished by burning. As a result, the part of the vanishing body becomes the space 90, and the protective layer 84 having the space 90 inside is formed. In this way, the protective layer 84 is formed on the element body 102 to obtain the sensor element 101. When the protective layer 84 is formed by gel casting, screen printing or dipping, the protective layer 84 is solidified or dried, and then the slurry is baked to form the protective layer 84. In this case, the protective layer 84 may be fired and the extinguishing body may be burned at the same time. When the protective layer 84 is formed by plasma spraying, the extinguishing body may be extinguished by burning after forming the protective layer 84.

  When forming the protective layer 84 (or the protective layer 84 before firing) provided with the disappearance body in the shape of the space 90, formation of a part of the protection layer 84 and formation of a part of the disappearance body are repeated. Then, the protective layer 84 and the vanishing body may be formed by gradually laminating the surface of the element body 102 in the thickness direction. The protective layer 84 may be formed by collectively forming the first to fifth protective layers 84a to 84e, or by forming the first to fifth protective layers 84a to 84e one by one. Good.

  When the sensor element 101 is obtained in this way, the gas sensor 100 is obtained by housing it in a predetermined housing and incorporating it in the main body (not shown) of the gas sensor 100.

  When the gas sensor 100 configured in this manner is used, the gas to be measured in the pipe reaches the sensor element 101, passes through the protective layer 84, and flows into the gas inlet 10. Then, the sensor element 101 detects the NOx concentration in the measured gas that has flowed into the gas inlet 10. At this time, the water contained in the measured gas may adhere to the surface of the protective layer 84. As described above, the element body 102 is adjusted to a temperature (for example, 800 ° C.) at which the solid electrolyte is activated by the heater 72, and when moisture adheres to the element 102, the temperature sharply decreases and cracks occur in the element body 102. May occur. Here, the protective layer 84 of the present embodiment has a space 90 inside. Thereby, the heat conduction in the thickness direction of the protective layer 84 (the direction from the outer peripheral surface of the protective layer 84 toward the element body 102) can be insulated by the space 90, and thus the element when water adheres to the surface of the protective layer 84. Cooling of the main body 102 is suppressed. Specifically, due to the presence of each of the upper space 91, the lower space 92, the left space 93, and the right space 94, water adheres to the upper, lower, left, and right surfaces of the protective layer 84. In this case, cooling of the element body 102 can be suppressed. Therefore, in this embodiment, the water resistance of the element body 102 is improved.

  Here, the correspondence relationship between the components of the present embodiment and the components of the present invention will be clarified. The element body 102 of the present embodiment corresponds to the element body of the present invention, the outer pump electrode 23 corresponds to the outer electrode, the lower space 92 corresponds to the exposed space, and the protective layer 84 corresponds to the protective layer.

  According to the gas sensor 100 of the present embodiment described in detail above, the sensor element 101 includes a long rectangular parallelepiped element body 102 having an oxygen ion conductive solid electrolyte layer and a first surface 102a of the element body 102. At least one exposed space (lower space) that covers at least a part of the arranged outer pump electrode 23 and the second surface 102b of the element body 102 opposite to the first surface 102a, and exposes the second surface 102b. 92) having a protective layer 84. Thereby, the heat conduction in the thickness direction of the protective layer 84 (in particular, the heat conduction from the lower surface of the second protective layer 84b to the upper side) can be insulated by the lower space 92, so that the surface of the protective layer 84 is protected from water. Cooling of the element body 102 when adhered is suppressed. Therefore, the water resistance of the element body 102 is improved. In this embodiment, as shown in FIG. 2, the heater 72 is arranged below the vertical center of the element body 102. That is, the heater 72 is arranged at a position closer to the second surface 102b than the first surface 102a. Therefore, the second surface 102b is likely to have a relatively high temperature. Therefore, it is highly significant that the protective layer 84 includes the lower space 92 on the second surface 102b side. In addition, the presence of each of the upper space 91, the left space 93, and the right space 94 allows the element body 102 when water adheres to the surfaces of the first, third, and fourth protective layers 84a, 84c, and 84d. Since the cooling of the element body 102 can be suppressed, the water resistance of the element body 102 is further improved.

  Further, the lower space 92 is located so as to overlap with the center of the region of the second surface 102b covered with the protective layer 84 when viewed from the direction perpendicular to the second surface 102b. Here, the center of the region covered with the protective layer 84 is likely to have a relatively high temperature, and the portion far from the center (for example, a portion near the end of the second surface 102b) is relatively hard to have a relatively high temperature. Therefore, by insulating the center of the region of the second surface 102b covered by the protective layer 84 with the lower space 92, the water resistance of the element body 102 is further improved.

[Second Embodiment]
FIG. 6 is a sectional view of the sensor element 101A of the second embodiment. FIG. 7 is a sectional view taken along line EE of FIG. The sensor element 101A has a space 90A in which the protective layer 84 is different from the space 90, and is otherwise the same as the sensor element 101 of the first embodiment.

  The space 90A has an upper space 91A, a lower space 92A, a left space 93A, and a right space 94A. The upper space 91A is the same as the upper space 91 of the first embodiment except that the upper space 91A further includes a communication hole H1 that opens to the upper surface of the first protective layer 84a. Similarly, each of the spaces 92A to 94A is the same as each of the spaces 92 to 94 of the first embodiment except that the spaces 92A to 94A further include communication holes H2 to H4 that open to the outer surface of the protective layer 84.

  The communication hole H2 is a rectangular parallelepiped space opened on the lower surface of the protective layer 84 in a substantially rectangular shape. However, the shape is not limited to this, and the opening may be circular, for example. Through this communication hole H2, the lower space 92A communicates with the outside of the protective layer 84. The position of the communication hole H2 may be the center in the front-rear direction or the center in the left-right direction of the region of the second surface 102b covered by the protective layer 84 when viewed from the direction perpendicular to the second surface 102b. It may be the center or the center (front, rear, left and right center).

  The positional relationship and shape of the communication holes H1, H3, H4 with respect to the corresponding first, third and fourth surfaces 102a, 102c, 102d are the same as the positional relationship and shape of the communication hole H2 with respect to the second surface 102b. . In addition, in this embodiment, the upper space 91A and the lower space 92A are vertically symmetrical in shape and arrangement. The left side space 93A and the right side space 94A have symmetrical shapes and arrangements.

  Like the sensor element 101, the sensor element 101A described above has the spaces 91A to 94A, so that the water resistance of the element body 102 is further improved. Further, the lower space 92A has an opening (opening of the communication hole H2) communicating with the outside of the second protective layer 84b. As a result, the heat in the lower space 92A can be released from the opening, so that overheating of the element body 102 is suppressed. Therefore, it is possible to suppress a rapid temperature decrease of the element body 102 when water adheres to the surface of the protective layer 84, and the water resistance of the element body 102 is improved. Similarly, since each of the spaces 91A, 93A, 94A has openings of the communication holes H1, H3, H4, the water resistance of the element body 102 is improved.

[Third Embodiment]
FIG. 8 is a sectional view of the sensor element 101B of the third embodiment. FIG. 9 is a sectional view taken along line FF of FIG. The sensor element 101B has a space 90B in which the protective layer 84 is different from the space 90, and is otherwise the same as the sensor element 101 of the first embodiment.

  The space 90B has an upper space 91B, a lower space 92B, a left space 93B, and a right space 94B. The lower space 92B is located in a plurality of exposed spaces 95B2 with the second surface 102b exposed, and a plurality of exposed spaces 95B2 displaced in a direction (downward) perpendicular to the second surface 102b with respect to the exposed space 95B2, and the second surface 102b is not exposed. And the non-exposed space 96B2. The exposed space 95B2 is a substantially rectangular parallelepiped space. As shown in FIG. 9, there are a total of 12 exposed spaces 95B2, three in the left-right direction and four in the front-rear direction, and they are arranged in a grid in a bottom view. The non-exposed space 96B2 is a substantially rectangular parallelepiped space. As shown in FIG. 9, there are 20 non-exposed spaces 96B2, four in the left-right direction and five in the front-rear direction, and they are arranged in a grid pattern in a bottom view. All of the plurality of exposed spaces 95B2 have the same vertical length. Further, all of the plurality of non-exposed spaces 96B2 have the same vertical length and the same vertical position. That is, the plurality of exposed spaces 95B2 and the plurality of non-exposed spaces 96B2 are arranged in two upper and lower stages.

The plurality of exposed spaces 95B2 and the plurality of unexposed spaces 96B2 are located at vertically separated heights so that their positions do not overlap with each other when viewed from a direction perpendicular to the vertical direction. Further, the plurality of exposure space 95B2 a plurality of unexposed spaces 96B2, is disposed at a position shifted to the position and the front-rear direction shifted in the lateral direction.

  The upper space 91B is located at a plurality of exposed spaces 95B1 with the first surface 102a exposed, and a plurality of exposed spaces 95B1 displaced in the direction (upward) perpendicular to the first surface 102a with respect to the exposed space 95B1 and the first surface 102a is not exposed. And an unexposed space 96B1. The left space 93B is located in a plurality of exposed spaces 95B3 with the third surface 102c exposed, and a plurality of exposed spaces 95B3 displaced in the direction (left side) perpendicular to the third surface 102c with respect to the exposed space 95B3, and the third surface 102c is not exposed. And a non-exposed space 96B3. The right side space 94B is located in a plurality of exposed spaces 95B4 with the fourth surface 102d exposed, and a plurality of exposed spaces 95B4 displaced in the direction (right side) perpendicular to the fourth surface 102d with respect to the exposed space 95B4, and the fourth surface 102d is not exposed. And a non-exposed space 96B4. The positional relationship and shape of the exposed spaces 95B1, 95B3, 95B4, and the non-exposed spaces 96B1, 96B3, 96B4 with respect to the corresponding first, third, and fourth surfaces 102a, 102c, 102d are the same as the exposure on the second surface 102b. This is the same as the positional relationship and shape of the space 95B2 and the non-exposed space 96B2. In this embodiment, there are four exposed spaces 95B3 and 95B4, one in the vertical direction and four in the front-back direction. In addition, the non-exposed spaces 96B3 and 96B4 are respectively two in the vertical direction and five in the front-back direction, for a total of ten. In addition, in the present embodiment, the upper space 91B and the lower space 92B have vertically symmetrical shapes and arrangements. The left-side space 93B and the right-side space 94B have a bilaterally symmetrical shape and arrangement.

  Like the sensor element 101, the sensor element 101B described above has the spaces 91B to 94B, so that the water resistance of the element body 102 is further improved. In addition, the second protective layer 84b is positioned in a direction perpendicular to the second surface 102b with respect to the plurality of exposed spaces 95B2 and at least one of the plurality of exposed spaces 95B2, and the second surface 102b is not exposed. And an unexposed space 96B2. When such a plurality of spaces are provided in the second protective layer 84b, the strength of the second protective layer 84b is less likely to decrease than in the case where there is one space having the same total volume. Therefore, by providing a space in the second protective layer 84b, it is possible to improve the water resistance of the element body 102 and suppress the reduction in the strength of the second protective layer 84b due to the presence of the space. In addition, since there are a plurality of non-exposed spaces 96B2 that are displaced in a direction perpendicular to the plurality of exposed spaces 95B2, all the plurality of spaces having the same shape and number are displaced in the direction parallel to the second surface 102b. Compared with the case where the spaces are located (not displaced in the vertical direction), the spaces are easily separated from each other. Therefore, the reduction in strength of the second protective layer 84b can be further suppressed. The same effect can be obtained for each of the spaces 91B, 93B, 94B with the same configuration.

[Fourth Embodiment]
FIG. 10 is a cross-sectional view of the sensor element 101C of the fourth embodiment. 11 is a sectional view taken along line GG of FIG. The sensor element 101C has a space 90C in which the protective layer 84 is different from the space 90B, and is otherwise the same as the sensor element 101B in the third embodiment.

The space 90C has an upper space 91C, a lower space 92C, a left space 93C, and a right space 94C. The lower space 92C is located at a plurality of exposed spaces 95C2 where the second surface 102b is exposed and a plurality of exposed spaces 95C2 which are offset from the exposed space 95C2 in a direction (downward) perpendicular to the second surface 102b and where the second surface 102b is not exposed. And the non-exposed space 96C2. Similarly, each space 91C, 93C, 94C has a plurality of exposed space 95C1,95C3,95C4, a plurality of unexposed spaces 96C1,96C3, and 96 C4, a.

  The number, shape, and arrangement of the non-exposed space 96C2 are the same as those of the non-exposed space 96B2 of the third embodiment. Similarly, the number, shape, and arrangement of the non-exposed spaces 96C1, 96C3, 96C4 are the same as the non-exposed spaces 96B1, 96B3, 96B4 of the third embodiment.

  The plurality of exposed spaces 95C2 are displaced from the plurality of unexposed spaces 96C2 in the direction perpendicular to the second surface 102b and in the front-rear direction, but the positions in the left-right direction are the same. This is different from the positional relationship between the exposed space 95B2 and the non-exposed space 96B2 of the third embodiment. As shown in FIG. 11, there are 16 exposed spaces 95C2, four in the left-right direction and four in the front-rear direction, and are arranged in a grid shape in a bottom view.

  Similarly, the plurality of exposed spaces 95C1, 95C3, 95C4 have the same horizontal position as the corresponding plurality of unexposed spaces 96C1, 96C3, 96C4. The positional relationship and shape of the exposed spaces 95C1, 95C3, and 95C4 with respect to the corresponding first, third, and fourth surfaces 102a, 102c, and 102d are the same as the positional relationship and shape of the exposed space 95C2 with respect to the second surface 102b. It is the same. In the present embodiment, the exposed spaces 95C3 and 95C4 are two in the vertical direction and four in the front-back direction, for a total of eight. In addition, in the present embodiment, the upper space 91C and the lower space 92C have vertically symmetrical shapes and arrangements. The left side space 93C and the right side space 94C have a symmetrical shape and arrangement.

  The sensor element 101C described above has the same configuration as the sensor element 101 and the sensor element 101B, and the same effect can be obtained.

[Fifth Embodiment]
FIG. 12 is a sectional view of the sensor element 101D of the fifth embodiment. FIG. 13 is a sectional view taken along line HH of FIG. The sensor element 101D has a space 90D in which the protective layer 84 is different from the space 90, and is otherwise the same as the sensor element 101 of the first embodiment.

  The space 90D has an upper space 91D, a lower space 92D, a left space 93D, and a right space 94D. The upper space 91D is the same as the upper space 91 of the first embodiment except that a plurality of columnar portions P1 that support the upper space 91D in the direction perpendicular to the first surface 102a are formed. Similarly, each of the spaces 92D to 94D is the first except that a plurality of columnar portions P2 to P4 supporting the respective spaces are formed in a direction perpendicular to the corresponding second surface to fourth surface 102b to 102d. It is the same as each of the spaces 92 to 94 in the embodiment.

  The columnar portion P2 is a part of the second protective layer 84b, and has a rectangular columnar shape. The shape of the columnar portion P2 is not limited to this, and may be a columnar shape, a triangular columnar shape, a pentagonal or higher polygonal columnar shape, or the like. As shown in FIG. 13, the plurality of columnar portions P2 are farther from the center in the front-rear direction of the region of the second surface 102b covered with the protective layer 84 when viewed from the direction perpendicular to the second surface 102b. The columnar portions P2 are arranged so that the density of the columnar portions P2 tends to increase. More specifically, it is arranged such that the number of columnar portions P2 per unit area increases as the distance from the center in the front-rear direction increases (the plurality of columnar portions P2 tend to be dense). In other words, the plurality of columnar portions P2 are arranged such that the number of the columnar portions P2 per unit area increases as they are closer to the front end and the rear end of the region of the second surface 102b covered by the protective layer 84. ing.

  The positional relations and shapes of the columnar portions P1, P3, P4 with respect to the corresponding first, third and fourth surfaces 102a, 102c, 102d are similar to the positional relations and shapes of the columnar portion P2 with respect to the second surface 102b. . For example, when the columnar portion P1 is viewed from a direction perpendicular to the first surface 102a, the columnar portion P1 per unit area becomes farther from the center in the front-rear direction of the region of the first surface 102a covered by the protective layer 84. The numbers are arranged in a tendency to increase. When the columnar portion P3 is viewed from a direction perpendicular to the third surface 102c, the number of the columnar portion P3 per unit area becomes farther from the front-rear center of the region of the third surface 102c covered by the protective layer 84. Are arranged in a tendency to increase. When viewed from a direction perpendicular to the fourth surface 102d, the columnar portion P4 has the number of the columnar portions P4 per unit area as it is farther from the center of the region of the fourth surface 102d covered by the protective layer 84 in the front-rear direction. Are arranged in a tendency to increase. In addition, in the present embodiment, the plurality of columnar portions P1 and the plurality of columnar portions P2 have vertically symmetrical shapes and arrangements. The plurality of columnar portions P3 and the plurality of columnar portions P4 have a bilaterally symmetrical shape and arrangement.

  Like the sensor element 101, the sensor element 101D described above has the spaces 91D to 94D, so that the water resistance of the element body 102 is further improved. Further, the second protective layer 84b has, for the lower space 92D, one or more columnar portions P2 that support the lower space 92D in a direction perpendicular to the second surface 102b. Therefore, since the columnar portion P2 supports the lower space 92D, it is possible to suppress the decrease in strength of the second protective layer 84b. Further, the second protective layer 84b has a plurality of columnar portions P2, and the plurality of columnar portions P2 are columnar as they are farther from the center of the region of the second surface 102b covered by the second protective layer 84b. It is arranged such that the density of the portion P2 tends to increase. Here, the center of the region covered by the second protective layer 84b is likely to have a relatively high temperature, and the part far from the center (for example, a part near the end of the second surface 102b) is relatively unlikely to have a high temperature. Therefore, by making the density of the columnar portions P2 higher in the portion where the temperature is relatively less likely to rise, the columnar portion P2 suppresses the decrease in the strength of the second protective layer 84b, while the region in which the temperature is likely to rise becomes columnar. It is possible to suppress a decrease in the heat insulating effect of the lower space 92D due to the presence of the portion P2. Therefore, the water resistance of the element body 102 can be further improved while further suppressing the decrease in the strength of the second protective layer 84b. The same effect can be obtained for each of the spaces 91D, 93D, and 94D with the same configuration.

[Sixth Embodiment]
FIG. 14: is sectional drawing of the sensor element 101E of 6th Embodiment. FIG. 15 is a sectional view taken along line I-I of FIG. 14. In the sensor element 101E, the protective layer 84 has a space 90E different from the space 90D, and the other points are the same as the sensor element 101D of the fifth embodiment.

  The space 90E has an upper space 91E, a lower space 92E, a left space 93E, and a right space 94E. The spaces 91E to 94E are the same as the spaces 91D to 94D of the fifth embodiment, except that the arrangement and number of the columnar portions P1 to P4 supporting the spaces 91E to 94E are different.

  As shown in FIG. 15, the plurality of columnar portions P2 are closer to the center in the front-rear direction of the region of the second surface 102b covered with the protective layer 84 when viewed from the direction perpendicular to the second surface 102b. The columnar portions P2 are arranged so that the density of the columnar portions P2 tends to increase. More specifically, they are arranged so that the number of the columnar portions P2 per unit area increases as they are closer to the center in the front-rear direction (the plurality of columnar portions P2 tend to be dense).

  The positional relations and shapes of the columnar portions P1, P3, P4 with respect to the corresponding first, third and fourth surfaces 102a, 102c, 102d are similar to the positional relations and shapes of the columnar portion P2 with respect to the second surface 102b. . For example, when viewed from a direction perpendicular to the first surface 102a, the pillar portion P1 is closer to the center in the front-rear direction of the region of the first surface 102a covered by the protective layer 84, and thus the pillar portion P1 per unit area. The numbers are arranged in a tendency to increase. When the columnar portion P3 is viewed from a direction perpendicular to the third surface 102c, the number of the columnar portion P3 per unit area is closer to the center in the front-rear direction of the region of the third surface 102c covered by the protective layer 84. Are arranged in a tendency to increase. When the columnar portion P4 is viewed from a direction perpendicular to the fourth surface 102d, the number of the columnar portion P4 per unit area is closer to the center of the region of the fourth surface 102d covered by the protective layer 84 in the front-rear direction. Are arranged in a tendency to increase. In addition, in the present embodiment, the plurality of columnar portions P1 and the plurality of columnar portions P2 have vertically symmetrical shapes and arrangements. The plurality of columnar portions P3 and the plurality of columnar portions P4 have a bilaterally symmetrical shape and arrangement.

Similarly to the sensor element 101, the sensor element 101E described above has the spaces 91E to 94E, so that the water resistance of the element body 102 is further improved. Further, since the columnar portion P2 supports the lower space 92E, it is possible to suppress the decrease in the strength of the second protective layer 84b. The same effect can be obtained for each of the spaces 91 E , 93 E , and 94 E with the same configuration.

[Seventh Embodiment]
FIG. 16 is a sectional view of the sensor element 101F of the seventh embodiment. FIG. 17 is a sectional view taken along line JJ of FIG. 18 is a sectional view taken along line KK of FIG. The sensor element 101F has a space 90F in which the protective layer 84 is different from the space 90, and is otherwise the same as the sensor element 101 of the first embodiment.

  The space 90F has an upper space 91F, a lower space 92F, a left space 93F, and a right space 94F. As shown in FIG. 17, in the lower space 92F, the first exposed space 97F2, which is an exposed space whose longitudinal direction is along the longitudinal direction (front-back direction) of the second surface 102b, is arranged in the lateral direction of the second surface 102b ( A plurality of them along the left-right direction). The lower space 92F has a second exposure space 98F2, which is an exposure space whose longitudinal direction extends along the lateral direction of the second surface 102b and intersects the first exposure space 97F2, along the longitudinal direction of the second surface 102b. Have more than one. In the present embodiment, it is assumed that there are two first exposed spaces 97F2 and five second exposed spaces 98F2. The plurality of second exposure spaces 98F2 are located at equal intervals in the front-rear direction.

  The first exposed space 97F2 and the second exposed space 98F2 are both substantially rectangular parallelepiped spaces. The first exposed space 97F2 has a slit shape, and one side (side in the left-right direction) along the lateral direction of the second surface 102b is the other two sides (side in the up-down direction and the front-back direction). ) Shorter than. The second exposed space 98F2 has a slit shape, and one side (the side in the front-back direction) along the longitudinal direction of the second surface 102b is more than the other two sides (the side in the vertical direction and the side in the horizontal direction). short.

  The upper space 91F has a plurality of first exposure spaces 97F1 and a plurality of second exposure spaces 98F1 similarly to the lower space 92F. The left space 93F has a plurality of first exposure spaces 97F3 and a plurality of second exposure spaces 98F3, like the lower space 92F. The right space 94F has a plurality of first exposure spaces 97F4 and a plurality of second exposure spaces 98F4, like the lower space 92F.

The positional relationship and shape of each of the first exposed spaces 97F1, 97F3, 97F4 and each of the second exposed spaces 98F1, 98F3, 98F4 with respect to the corresponding first, third and fourth surfaces 102a, 102c, 102d are the second surface. The positional relationship and shape of the first exposure space 97F2 and the second exposure space 9 8 F2 with respect to 102b are similar. For example, the plurality of first exposed spaces 97F1, 97F3, 97F4 are along the longitudinal direction (front-rear direction) of the corresponding first, third and fourth surfaces 102a, 102c, 102d. The plurality of second exposed spaces 98F1, 98F3, 98F4 are along the lateral direction of the corresponding first, third and fourth surfaces 102a, 102c, 102d in the longitudinal direction. Further, the plurality of first exposed spaces 97F1 and the plurality of second exposed spaces 98F1 intersect, the plurality of first exposed spaces 97F3 and the plurality of second exposed spaces 98F3 intersect, and the plurality of first exposed spaces 97F3. The exposed space 97F4 and the plurality of second exposed spaces 98F4 intersect. In addition, in the present embodiment, the upper space 91F and the lower space 92F have vertically symmetrical shapes and arrangements. The left-side space 93F and the right-side space 94F have symmetrical shapes and arrangements.

  Like the sensor element 101, the sensor element 101F described above has the spaces 91F to 94F, so that the water resistance of the element body 102 is further improved. In addition, the second protective layer 84b has a plurality of first exposed spaces 97F2 and a plurality of second exposed spaces 98F2. Since a plurality of elongated first exposed spaces 97F2 along the longitudinal direction of the second surface 102b are present along the lateral direction of the second surface 102b, heat generated between the second protective layer 84b and the element body 102 when exposed to water is increased. The stress due to the difference in expansion coefficient from the second protective layer 84b to the element body 102 along the lateral direction of the second surface 102b is reduced. In addition, since there are a plurality of elongated second exposed spaces 98F2 along the lateral direction of the second surface 102b along the longitudinal direction of the second surface 102b, the second protective layer 84b and the element body 102 when exposed to water are The stress from the second protective layer 84b to the element main body 102 along the longitudinal direction of the second surface 102b due to the difference in the thermal expansion coefficient is reduced. As a result, the element body 102 is less likely to break when exposed to water, and the water resistance of the element body 102 is further improved. Since each of the first, third, and fourth protective layers 84a, 84c, and 84d has the spaces 91F, 93F, and 94F, the same effect can be obtained with the same configuration.

[Eighth Embodiment]
FIG. 19 is a sectional view of the sensor element 101G of the eighth embodiment. 20 is a sectional view taken along line LL in FIG. In the sensor element 101G, the protective layer 84 has a space 90G. The space 90G has an upper space 91G, a lower space 92G, a left space 93G, and a right space 94G. The upper space 91G is the same as the upper space 91F of the seventh embodiment except that the upper space 91G includes a plurality of first exposure spaces 97F1 and does not include the second exposure space 98F1. Similarly, each of the spaces 92G to 94G includes a plurality of first exposed spaces 97F2 to 97F4, and does not include the second exposed spaces 98F2 to 98F4, respectively, and the respective spaces 92F to 94F of the seventh embodiment. Is the same as.

Like the sensor element 101, the sensor element 101G described above has the spaces 91G to 94G, so that the water resistance of the element body 102 is further improved. Further, since the second protective layer 84b has the plurality of first exposed spaces 97F2, the thermal expansion coefficient difference between the second protective layer 84b and the element body 102 when exposed to water is the same as in the seventh embodiment. The stress resulting from the second protective layer 84b with respect to the element body 102 in the lateral direction of the second surface 102b is reduced. As a result, the element body 102 is less likely to break when exposed to water, and the water resistance of the element body 102 is further improved. First, third, fourth protective layer 8 4 a, 84c, for also each 84d, respectively by the first exposure space 97F1,97F3,97F4 present, the same effect can be obtained.

[Ninth Embodiment]
FIG. 21 is a sectional view of the sensor element 101H of the ninth embodiment. 22 is a sectional view taken along line MM of FIG. In the sensor element 101H, the protective layer 84 has a space 90H. The space 90H has an upper space 91H, a lower space 92H, a left space 93H, and a right space 94H. The upper space 91H is the same as the upper space 91F of the seventh embodiment except that the upper space 91H includes a plurality of second exposure spaces 98F1 and does not include the first exposure space 97F1. Similarly, each of the spaces 92H to 94H includes a plurality of second exposed spaces 98F2 to 98F4, and does not include the first exposed spaces 97F2 to 97F4, respectively, and the respective spaces 92F to 94F of the seventh embodiment. Is the same as.

  Like the sensor element 101, the sensor element 101H described above has the spaces 91H to 94H, so that the water resistance of the element body 102 is further improved. Further, since the second protective layer 84b has the plurality of second exposed spaces 98F2, the difference in thermal expansion coefficient between the second protective layer 84b and the element body 102 when exposed to water is the same as in the seventh embodiment. The stress resulting from the second protective layer 84b with respect to the element body 102 along the longitudinal direction of the second surface 102b is reduced. As a result, the element body 102 is less likely to break when exposed to water, and the water resistance of the element body 102 is further improved. With respect to each of the first, third, and fourth protective layers 84a, 84c, 84d, the second exposed spaces 98F1, 98F3, 98F4 are present, respectively, so that the same effect can be obtained.

[Tenth Embodiment]
FIG. 23 is a sectional view of the sensor element 101I of the tenth embodiment. FIG. 24 is a bottom view of the vicinity of the front end of the sensor element 101I. Note that FIG. 23 shows the sensor element 101I as viewed from the lower right rear side. In the sensor element 101I, the protective layer 84 has a space 90I different from the space 90, and the other points are the same as the sensor element 101 of the first embodiment.

  The space 90I has a plurality of upper spaces 91I, lower spaces 92I, left spaces 93I, and right spaces 94I, respectively. The lower space 92I is an exposed space in which the second surface 102b is exposed. The lower space 92I is a space having a substantially triangular prism shape whose longitudinal direction extends along the longitudinal direction of the second surface 102b. The plurality of lower spaces 92I are arranged side by side (six in the present embodiment) along the lateral direction of the second surface 102b. As shown in FIG. 23, the lower space 92I has a triangular cross section (a cross section along the vertical and horizontal directions) perpendicular to the second surface 102b. Therefore, the lower space 92I has a shape such that the space becomes narrower as it goes away from the second surface 102b, that is, as it goes downward. Further, the lower space 92I has inner surfaces Sa2 and Sb2 that form two sides of a triangle facing the second surface 102b in a cross-sectional view perpendicular to the second surface 102b. The inner surfaces Sa2, Sb2 are inclined so that the inner surfaces Sa2, Sb2 are closer to each other as they are farther from the second surface 102b, that is, as they go downward.

The spaces 91I, 93I, 94I are exposed spaces in which the first, third, and fourth surfaces 102a, 102c, 102d are exposed, like the lower space 92I. Each space 91I, 93I, 94I, the first corresponding, third, fourth surface 102a, 102c, 10 corresponding inner surface constituting the two sides of the triangle facing the plane perpendicular cross section to 2 d It has Sa1, Sa3, Sa4 and inner surfaces Sb1, Sb3, Sb4. The positional relationship and shape of each space 91I, 93I, 94I with respect to the corresponding first, third and fourth surfaces 102a, 102c, 102d are similar to the positional relationship and shape of the lower space 92I with respect to the second surface 102b. is there. Two left spaces 93I and right spaces 94I are arranged side by side in the vertical direction. In the present embodiment, the plurality of upper spaces 91I and the plurality of lower spaces 92I have vertically symmetrical shapes and arrangements. The plurality of left space 93I and a plurality of right space 94I has a symmetrical shape and arrangement. Further, the plurality of the upper space 91 above the space 91I 4 pieces of the horizontal center of the I, the outer pumping electrode 23 is exposed.

  Like the sensor element 101, the sensor element 101I described above has the spaces 91I to 94I, so that the water resistance of the element body 102 is further improved. Further, the lower space 92I has a shape in which the space tends to become narrower as the distance from the second surface 102b increases. The lower space 92I having such a shape has a lower strength of the second protective layer 84b than a rectangular parallelepiped space having an inner surface parallel to the second surface 102b like the lower space 92 of FIG. Can be suppressed.

  Further, the lower space 92I has at least two inner surfaces Sa2, Sb2 that are inclined in a direction in which they approach each other as they are farther from the second surface 102b. The lower space 92I having such inner surfaces Sa2, Sb2 is larger than the second protective layer in comparison with a rectangular parallelepiped space having an inner surface parallel to the second surface 102b like the lower space 92 of FIG. The decrease in strength of 84b can be suppressed.

  Further, the second protective layer 84b has a plurality of lower spaces 92I whose longitudinal direction is along the longitudinal direction of the second surface 102b, along the lateral direction of the second surface 102b. Therefore, like the sensor elements 101F and 101G, the short distance of the second surface 102b from the second protective layer 84b to the element body 102 due to the difference in thermal expansion coefficient between the second protective layer 84b and the element body 102 when exposed to water. The stress along the hand direction is reduced. As a result, the element body 102 is less likely to break when exposed to water, and the water resistance of the element body 102 is further improved.

  Since the spaces 91I, 93I, and 94I exist in each of the first, third, and fourth protective layers 84a, 84c, and 84d, the same effect can be obtained by the same configuration as the second protective layer 84b. .

[Eleventh Embodiment]
FIG. 25: is sectional drawing of the sensor element 101J of 11th Embodiment. FIG. 26 is a bottom view around the front end of the sensor element 101J. Note that FIG. 25 shows the sensor element 101J as viewed from the lower right rear. The sensor element 101J has a space 90J in which the protective layer 84 is different from the space 90, and is otherwise the same as the sensor element 101 of the first embodiment. The space 90J has exposed spaces 95J1 to 95J6.

  The exposed space 95J2 is a space arranged below the element body 102, and the second surface 102b is exposed. The exposed space 95J2 is a semi-elliptical columnar space, and the inner surface (the inner surface of the protective layer 84, that is, the surface facing upward) facing the second surface 102b has a rectangular shape curved outward (downward) of the second protective layer 84b. It is a curved surface (a curved surface corresponding to a part of the inner peripheral surface of the cylinder). Therefore, the exposed space 95J2 has a semi-elliptical shape in a cross section perpendicular to the second surface 102b (a cross section along the up, down, left, and right directions), and the space becomes narrower as it is farther from the second surface 102b (as it goes downward). It has a trendy shape. The longitudinal direction of the exposed space 95J2 is along the longitudinal direction of the second surface 102b.

  The exposed space 95J1 is a space arranged on the upper side of the element body 102, and the first surface 102a is exposed. The exposed space 95J1 is a semi-elliptical columnar space, and the inner surface (the inside of the protective layer 84, that is, the surface facing downward) of the inner surface facing the first surface 102a has a rectangular shape curved to the outside (upper) of the first protective layer 84a. It is a curved surface (a curved surface corresponding to a part of the inner peripheral surface of the cylinder). The longitudinal direction of the exposed space 95J1 is along the longitudinal direction of the first surface 102a. The outer pump electrode 23 is wholly exposed in the exposed space 95J1. The exposed space 95J1 has a vertically symmetrical shape and arrangement with the exposed space 95J2.

  The exposed space 95J4 is a space arranged at the lower left of the element body 102, and the second surface 102b and the third surface 102c are exposed. The exposed space 95J4 has a shape in which a part of a cylinder is cut out. The exposed space 95J4 corresponds to a curved surface (a part of the inner peripheral surface of the cylinder) in which an inner surface (upward facing surface) facing the second surface 102b is a rectangle curved outward (downward) of the second protective layer 84b. Curved surface). Therefore, the exposed space 95J4 has a shape in which the space becomes narrower as it is farther from the second surface 102b (as it goes downward). The exposed space 95J4 is a curved surface (of the inner peripheral surface of the cylinder) in which the inner surface (the surface facing the right side) facing the third surface 102c is a rectangle curved outward (left side) of the third protective layer 84c. It is a curved surface corresponding to a part). Therefore, the exposed space 95J4 has a shape in which the space becomes narrower as it is farther from the third surface 102c (to the left). The longitudinal direction of the exposed space 95J4 is along the longitudinal direction of the second surface 102b and the third surface 102c.

  The exposed space 95J3 is a space arranged at the upper left of the element body 102, and the first surface 102a and the third surface 102c are exposed. The exposed space 95J3 has a vertically symmetrical shape and arrangement with the exposed space 95J4. The exposed space 95J5 is a space arranged on the upper right of the element body 102, and the first surface 102a and the fourth surface 102d are exposed. The exposed space 95J5 has a shape and arrangement that are symmetrical to the exposed space 95J3. The exposed space 95J6 is a space arranged at the lower right of the element body 102, and the second surface 102b and the fourth surface 102d are exposed. The exposure space 95J6 has a shape and arrangement that is symmetrical with respect to the exposure space 95J4, and has a shape and arrangement that is vertically symmetrical with respect to the exposure space 95J5.

  The exposed spaces 95J1, 95J3, 95J5 are arranged along the lateral direction of the first surface 102a. The exposed spaces 95J2, 95J4, 95J6 are arranged along the lateral direction of the second surface 102b. The exposed spaces 95J3 and 95J4 are arranged along the lateral direction of the third surface 102c. The exposed spaces 95J5 and 95J6 are arranged along the lateral direction of the fourth surface 102d.

  Like the sensor element 101, the sensor element 101J described above has the exposed spaces 95J1 to 95J6, so that the water resistance of the element body 102 is further improved. The exposed spaces 95J2, 95J4, 95J6 are shaped so that the space becomes narrower as the distance from the second surface 102b increases. Further, in the exposed spaces 95J2, 95J4, 95J6, the inner surface facing the second surface 102b is a curved surface curved outward. The space having such a shape can suppress a decrease in strength of the second protective layer 84b, as compared with a space having a rectangular parallelepiped shape having an inner surface parallel to the second surface 102b, such as the lower space 92 in FIG. .

  In addition, the protective layer 84 has exposure spaces 95J2, 95J4, 95J6, which are a plurality of exposure spaces whose longitudinal direction is along the longitudinal direction of the second surface 102b, arranged side by side along the lateral direction of the second surface 102b. There is. Therefore, like the sensor elements 101F and 101G, the short distance of the second surface 102b from the second protective layer 84b to the element body 102 due to the difference in thermal expansion coefficient between the second protective layer 84b and the element body 102 when exposed to water. The stress along the hand direction is reduced. As a result, the element body 102 is less likely to break when exposed to water, and the water resistance of the element body 102 is further improved.

  The exposed spaces 95J1, 95J3, 95J5 for the first surface 102a, the exposed spaces 95J3, 95J4 for the third surface 102c, and the exposed spaces 95J5, 95J6 for the fourth surface 102d are also exposed spaces 95J2, 95J4, 95J6 for the second surface 102b. The same effect can be obtained by the configuration similar to.

[Twelfth Embodiment]
FIG. 27 is a sectional view of the sensor element 101K of the twelfth embodiment. FIG. 28 is a bottom view around the front end of the sensor element 101K. Note that FIG. 27 shows the sensor element 101K as viewed from the lower right rear side. The sensor element 101K has a space 90K in which the protective layer 84 is different from the space 90, and is otherwise the same as the sensor element 101 of the first embodiment. The space 90K has exposed spaces 95K1 to 95K4.

  The exposed spaces 95K1 and 95K2 are the same as the exposed spaces 95J1 and 95J2 of the sensor element 101J, respectively.

  The exposed space 95K3 is a space that is arranged over the upper side, the lower side, and the left side of the element body 102, and the first surface 102a, the second surface 102b, and the third surface 102c are exposed. The exposed space 95K3 has a shape in which a part of an elliptic cylinder is cut out. The exposed space 95K3 corresponds to a curved surface (a part of the inner peripheral surface of the cylinder) in which the inner surface (the surface facing downward) of the first surface 102a is a rectangle curved outward (upward) of the first protective layer 84a. Curved surface). Therefore, the exposed space 95K3 has a shape in which the space becomes narrower as it is farther from the first surface 102a (as it goes upward). The exposed space 95K3 corresponds to a curved surface (a part of the inner peripheral surface of the cylinder) in which the inner surface (the surface facing upward) of the second surface 102b is curved to the outside (downward) of the second protective layer 84b. Curved surface). Therefore, the exposed space 95K3 has a shape such that the space becomes narrower as it is farther from the second surface 102b (as it goes downward). The exposed space 95K3 is a curved surface (of the inner peripheral surface of the cylinder) in which the inner surface (the surface facing the right side) facing the third surface 102c is a rectangle curved outward (to the left) of the third protective layer 84c. It is a curved surface corresponding to a part). Therefore, the exposed space 95K3 has a shape in which the space becomes narrower as it is farther from the third surface 102c (to the left). The exposed space 95K3 has a longitudinal direction along the longitudinal direction of the first surface 102a, the second surface 102b, and the third surface 102c.

  The exposed space 95K4 is a space that is arranged over the upper side, the lower side, and the right side of the element body 102, and the first surface 102a, the second surface 102b, and the fourth surface 102d are exposed. The exposed space 95K4 has a shape and an arrangement that are symmetrical to the exposed space 95K3.

  The exposed spaces 95K1, 95K3, 95K4 are arranged along the lateral direction of the first surface 102a. The exposed spaces 95K2, 95K3, 95K4 are arranged along the lateral direction of the second surface 102b.

  Similarly to the sensor element 101, the sensor element 101K described above has the exposed spaces 95K1 to 95K4, so that the water resistance of the element body 102 is further improved. The exposed spaces 95K2, 95K3, 95K4 have a shape in which the space tends to become narrower as the distance from the second surface 102b increases. Further, the exposed spaces 95K2, 95K3, 95K4 are curved surfaces in which the inner surface facing the second surface 102b is curved outward. The space having such a shape can suppress a decrease in strength of the second protective layer 84b, as compared with a space having a rectangular parallelepiped shape having an inner surface parallel to the second surface 102b, such as the lower space 92 in FIG. . The exposed spaces 95K1, 95K3, 95K4 for the first surface 102a, the exposed space 95K3 for the third surface 102c, and the exposed space 95K4 for the fourth surface 102d are similar to the exposed spaces 95K2, 95K3, 95K4 for the second surface 102b. As a result, a similar effect, that is, an effect of suppressing a decrease in strength of the first, third, and fourth protective layers 84a, 84c, 84d can be obtained.

  The protective layer 84 also has exposed spaces 95K1, 95K3, 95K4, which are a plurality of exposed spaces whose longitudinal direction is along the longitudinal direction of the first surface 102a, and are arranged along the lateral direction of the first surface 102a. There is. Therefore, like the sensor elements 101F and 101G, the short distance of the first surface 102a from the first protective layer 84a to the element body 102 due to the difference in thermal expansion coefficient between the first protective layer 84a and the element body 102 when exposed to water. The stress along the hand direction is reduced. As a result, the element body 102 is less likely to break when exposed to water, and the water resistance of the element body 102 is further improved. Further, the protective layer 84 has exposed spaces 95K2, 95K3, 95K4, which are a plurality of exposed spaces whose longitudinal direction is along the longitudinal direction of the second surface 102b, arranged side by side along the lateral direction of the second surface 102b. There is. Therefore, similarly to the sensor elements 101F and 101G, the stress from the second protective layer 84b to the element body 102 along the lateral direction of the second surface 102b is reduced. As a result, the element body 102 is less likely to break when exposed to water, and the water resistance of the element body 102 is further improved.

  Note that each space in the protective layer 84 of the above-described second to twelfth embodiments can also be formed by using a vanishing material that vanishes by combustion, as in the first embodiment.

  It is needless to say that the present invention is not limited to the above-described embodiments and can be implemented in various modes as long as they are within the technical scope of the present invention.

  For example, in the above-described first embodiment, the lower space 92 is arranged so as to overlap the center of the region of the second surface 102b covered with the protective layer 84 when viewed from the direction perpendicular to the second surface 102b. It was located, but is not limited to this. For example, when viewed from the direction perpendicular to the second surface 102b, the lower space 92 overlaps with the center in the front-rear direction of the region of the second surface 102b covered by the protective layer 84, and does not coincide with the center in the left-right direction. It may not overlap, it may overlap with the center in the left-right direction and may not overlap with the center in the front-rear direction, or it may not overlap with the center in the left-right direction and the center in the front-rear direction. Good.

  In the above-described first embodiment, the maximum temperature region in the second surface 102b in a state where the element body 102 is heated to the temperature at the time of normal driving (for example, 800 ° C.) by the heater 72 is set as the maximum temperature region. The side space 92 may be positioned so as to overlap this maximum temperature region when viewed from the direction perpendicular to the second surface 102b. By doing so, the lower space 92 can insulate the region of the second surface 102b that has the highest temperature when the sensor element 101 is used, and thus the water resistance of the element body is further improved.

  In the above-described second embodiment, each of the spaces 91A to 94A has one communication hole H1 to H4, but this is not the only option. One space may have a plurality of communication holes. In addition, when the protective layer 84 has a plurality of spaces, there may be a space that is open to the outside and a space that is not open.

  In the above-described third embodiment, the exposed space 95B2 and the non-exposed space 96B2 are located at vertically separated heights so that their positions do not overlap with each other when viewed from the direction perpendicular to the vertical direction. However, the positions are not limited to this, and the positions may partially overlap each other when viewed from a direction perpendicular to the vertical direction. Further, although the exposed space 95B2 and the non-exposed space 96B2 are positioned deviated in the front-rear direction, the positions in the front-rear direction may be the same. For example, the exposed space 95B2 and the non-exposed space 96B2 may be vertically displaced and the front, rear, left, and right positions may be the same. Further, the space 90B has a space arranged in two steps of an inner side and an outer side (for example, an exposed space 95B2 and a non-exposed space 96B2), but is not limited to this and has a space arranged in three or more steps. May be. Further, the vertical heights may be different among the plurality of non-exposed spaces 96B2. In addition, in the third embodiment, the protective layer 84 may not include the non-exposed spaces 96B1 to 96B4. Further, in the third embodiment, when viewed from a direction perpendicular to the second surface 102b, the exposed space 95B2 tends to have a higher density as it is closer to the center of the region of the second surface 102b covered by the protective layer 84. Alternatively, the non-exposed space 96B2 may be arranged. By doing so, the heat insulating property of the portion that is likely to reach a relatively high temperature can be improved, and the water resistance of the element body 102 is improved. In addition, "the tendency that the density of the space becomes high" includes the tendency that the number of spaces per unit area becomes large and the tendency that the space becomes large. Note that the above modified example can be similarly applied to the fourth embodiment.

  In the fifth and sixth embodiments described above, the density of the columnar portions P2 is changed by changing the number of the plurality of columnar portions P2 per unit area, but the thickness of the columnar portions P2 is not limited to this. By doing so, the density of the columnar portions P2 may be changed. Further, the density of the columnar portion P2 does not have to be particularly changed depending on the place.

  In the above-described fifth embodiment, the plurality of columnar portions P2 are far from the center in the front-rear direction of the region of the second surface 102b covered with the protective layer 84 when viewed from the direction perpendicular to the second surface 102b. Although the columnar portions P2 are arranged so that the density of the columnar portions P2 increases, the present invention is not limited to this, and the columnar portions P2 may be arranged such that the density of the columnar portions P2 increases as the distance from the center in the left-right direction increases. It may be arranged such that the density of the columnar portions P2 becomes higher as it is farther from. Regarding the arrangement of the columnar portions P2 in the sixth embodiment, similarly, the density may be changed not only in the front-rear direction but also in the left-right direction.

In the above-described seventh embodiment, one side of the first exposed space 97F2 along the lateral direction of the second surface 102b is shorter than the other two sides, but the first exposed space 97F2 is not limited to this. The longitudinal direction may be along the longitudinal direction of the second surface 102b. Similarly, in the seventh embodiment, one side of the second exposed space 98F2 along the longitudinal direction of the second surface 102b is shorter than the other two sides, but it is not limited to this. The longitudinal direction of the second exposed space 98F 2 may be along the lateral direction of the second surface 102b.

  In the eleventh embodiment described above, the exposed space 95J4 is arranged across the lower side and the left side of the element main body 102, but is not limited to this. For example, the protective layer 84 has, instead of the exposed space 95J4, a semi-elliptical columnar space arranged below the element body 102 and a semi-elliptical columnar space arranged on the left side of the element body 102. May be. The same applies to the exposed spaces 95J3, 95J5, 95J6 and the exposed spaces 95K3, 95K4 of the twelfth embodiment.

  In the tenth to twelfth embodiments described above, the longitudinal direction of each space provided in the protective layer 84 is along the front-rear direction, but the present invention is not limited to this. If the exposed space where the second surface 102b is exposed has a shape such that the space becomes narrower as it is farther from the second surface 102b, the effect of suppressing the decrease in strength of the second protective layer 84b can be obtained. For example, the lower space 92I in FIG. 23 may have a triangular pyramid shape. The exposed space 95J2 in FIG. 25 may have a hemispherical shape.

  In the above-described first to twelfth embodiments, the space located on the upper side of the element body 102 and the space located on the lower side are vertically symmetrical, and the space located on the left side of the element body 102 and the space located on the right side of the element body 102. Is assumed to be symmetrical, but is not limited to this. In each of the above-described first to twelfth embodiments, each of the first to fourth protective layers 84a to 84d has a space, but the present invention is not limited to this. The protective layer 84 may have one or more exposed spaces where the second surface 102b is exposed. For example, in the first embodiment, the protective layer 84 only needs to have the lower space 92, and may not have one or more of the upper space 91, the left space 93, and the right space 94. Further, the fifth protective layer 84e may have a space like the first to fourth protective layers 84a to 84d.

  In the above-described first to twelfth embodiments, the protective layer 84 has the first to fifth protective layers 84a to 84e, but the present invention is not limited to this. The protective layer 84 may have at least the second protective layer 84b. The second protective layer 84b may cover at least a part of the second surface 102b.

In the above-described embodiment, the size of each space provided in the protective layer 84 is not particularly described, but each space may have a size that can be distinguished from the pores of the protective layer 84. For example, the volume of each space may be 12500 μm ³ or more. Further, when the volume ratio of the space is defined as volume ratio = (total volume of space provided in the protective layer 84) / (volume of the protective layer 84) × 100, the volume ratio may be 60% or less. The above-mentioned “volume of the protective layer 84” is a value including the volume of the space provided in the protective layer 84.

Although not described in the above-described first to twelfth embodiments, the total volume of one or more spaces existing below the second surface 102b is preferably 0.03 mm ³ or more. In this case, the effect that the one or more spaces improve the water resistance of the element body can be more reliably obtained. For example, in the above-described first to tenth embodiments, the total volume of each of the lower spaces 92, 92A to 92I is preferably 0.03 mm ³ or more. In the eleventh embodiment, the total volume of the exposed space 95J2, the portion of the exposed space 95J4 located below the second surface 102b, and the portion of the exposed space 95J6 located below the second surface 102b. Is preferably 0.03 mm ³ or more. In the twelfth embodiment, the total volume of the exposed space 95K2, the portion of the exposed space 95K3 located below the second surface 102b, and the portion of the exposed space 95K4 located below the second surface 102b. Is preferably 0.03 mm ³ or more. Similarly, the total volume of one or more spaces existing above the first surface 102a is preferably 0.03 mm ³ or more. The total volume of one or more spaces existing on the left side of the third surface 102c is preferably 0.015 mm ³ or more. The total volume of the one or more spaces existing on the right side of the fourth surface 102d is preferably 0.015 mm ³ or more. It should be noted that “below the second surface 102b” is not limited to just below the second surface 102b, and includes, for example, lower left and lower right. Similarly, "above the first surface 102a" is not limited to just above the first surface 102a. The same applies to the “left side of the third surface 102c” and the “right side of the fourth surface 102d”.

Although not described in the above-described first to twelfth embodiments, when there is one or more spaces extending over two adjacent surfaces (surfaces sharing one side), the total volume of the one or more spaces is It is preferably 0.002 mm ³ or more. In this case, the effect that the one or more spaces improve the water resistance of the element body can be more reliably obtained. For example, in the eleventh embodiment, the volume of the exposed space 95J3 that straddles the first surface 102a and the third surface 102c is preferably 0.002 mm ³ or more. Similarly, an exposure space 95J4 extending over the second surface 102b and the third surface 102c, an exposure space 95J5 extending over the first surface 102a and the fourth surface 102d, and an exposure space 95J6 extending over the second surface 102b and the fourth surface 102d. Also, regarding each, it is preferable that each volume is 0.002 mm ³ or more. In addition, "a space extending over two adjacent surfaces" means a space existing in each of the directions perpendicular to each of the two surfaces. For example, the exposed space 95J4 exists in both the direction perpendicular to the second surface 102b (downward) and the direction perpendicular to the third surface 102c (leftward), and the second surface 102b and the third surface 102c are present. It is a space that spans across.

  The protective layer 84 may be provided by appropriately combining two or more of the spaces 90, 90A to 90K of the above-described first to twelfth embodiments and the spaces of the modified examples thereof. The combination in this case includes a case where the protective layer 84 has different types of spaces, and a case where the protective layer 84 has a space having the above-described characteristics of the shape and arrangement of the different types of spaces.

For example, at least one of the spaces other than the second embodiment may have an opening that communicates with the outside of the protective layer 84. When the opening is provided in the space, a communication hole for communicating the space with the outside may be provided like the communication holes H1 to H4 of the second embodiment, or the space may be extended to the surface of the protective layer 84 to leave the space as it is. It may be opened to the outside. It is preferable that the opening of the space has an appropriate size so that water can be prevented from directly entering the inside and heat in the space can be released from the opening. For example, it may be an open area as 100μm ² ~1000μm ^2.

  For example, in each space of the embodiments other than the first embodiment, at least one of the exposed spaces is covered with the protective layer 84 of the second surface 102b when viewed from the direction perpendicular to the second surface 102b. It may be located so as to overlap with the center of the region.

  1 1st substrate layer, 2 2nd substrate layer, 3 3rd substrate layer, 4 1st solid electrolyte layer, 5 spacer layer, 6 2nd solid electrolyte layer, 10 gas inlet port, 11 1st diffusion control part, 12 buffer Space, 13 2nd diffusion control part, 20 1st internal space, 21 main pump cell, 22 inner pump electrode, 22a ceiling electrode part, 22b bottom electrode part, 23 outer pump electrode, 25 variable power supply, 30 3rd diffusion control part , 40 second internal space, 41 measuring pump cell, 42 reference electrode, 43 reference gas introducing space, 44 measuring electrode, 45 fourth diffusion controlling part, 46 variable power source, 48 atmosphere introducing layer, 50 auxiliary pump cell, 51 auxiliary pump Electrode, 51a ceiling electrode part, 51b bottom electrode part, 52 variable power source, 70 heater part, 71 heater connector electrode, 72 heater, 73 through hole, 74 heater Insulating layer, 75 Pressure diffusion hole, 80 Main pump control oxygen partial pressure detection sensor cell, 81 Auxiliary pump control oxygen partial pressure detection sensor cell, 82 Measurement pump control oxygen partial pressure detection sensor cell, 83 Sensor cell, 84 Protective layer, 84a -84e 1st-5th protective layer, 90,90A-90K space, 91,91A-91I upper space, 92,92A-92I lower space, 93,93A-93I left space, 94,94A-94I right space, 95B1-95B4, 95C1-95C4, 95J1-95J6, 95K1-95K4 exposed space, 96B1-96B4, 96C1-96C4 non-exposed space, 97F1-97F4 first exposed space, 98F1-98F4 second exposed space, 100 gas sensor, 101, 101A to 101K sensor element, 102 element body, 10 The first surface to the sixth surface a~102f, H1~H4 hole, P1 to P4 columnar portion, Sa1~Sa4, Sb1~Sb4 surface.

Claims (14)

A long rectangular parallelepiped-shaped element body provided with an oxygen ion conductive solid electrolyte layer,
An outer electrode disposed on the first surface, which is one of the surfaces of the element body,
A protective layer which covers at least a part of a second surface of the element body opposite to the first surface, and which has one or more exposed spaces where the second surface is exposed;
Equipped with
The protective layer is a porous body having a plurality of pores,
The one or more exposed spaces are spaces different from the pores, and each volume is 12500 μm ³ or more,
At least one of the exposed spaces has an opening that communicates with the outside of the protective layer,
Sensor element. A long rectangular parallelepiped-shaped element body provided with an oxygen ion conductive solid electrolyte layer,
An outer electrode disposed on the first surface, which is one of the surfaces of the element body,
A protective layer which covers at least a part of a second surface of the element body opposite to the first surface, and which has one or more exposed spaces where the second surface is exposed;
Equipped with
The protective layer is a porous body having a plurality of pores,
The one or more exposed spaces are spaces different from the pores, and each volume is 12500 μm ³ or more,
The protective layer includes a plurality of exposed spaces, and a plurality of non-exposed spaces that are offset from at least one of the plurality of exposed spaces in a direction perpendicular to the second surface and do not expose the second surface. ,have,
Sensor element. A long rectangular parallelepiped-shaped element body provided with an oxygen ion conductive solid electrolyte layer,
An outer electrode disposed on the first surface, which is one of the surfaces of the element body,
A protective layer which covers at least a part of a second surface of the element body opposite to the first surface, and which has one or more exposed spaces where the second surface is exposed;
Equipped with
The protective layer is a porous body having a plurality of pores,
The one or more exposed spaces are spaces different from the pores, and each volume is 12500 μm ³ or more,
The protective layer has a plurality of exposed spaces whose longitudinal direction is along the longitudinal direction of the second surface, along the lateral direction of the second surface.
Sensor element. A long rectangular parallelepiped-shaped element body provided with an oxygen ion conductive solid electrolyte layer,
An outer electrode disposed on the first surface, which is one of the surfaces of the element body,
A protective layer which covers at least a part of a second surface of the element body opposite to the first surface, and which has one or more exposed spaces where the second surface is exposed;
Equipped with
The protective layer is a porous body having a plurality of pores,
The one or more exposed spaces are spaces different from the pores, and each volume is 12500 μm ³ or more,
The protective layer has a plurality of the exposed spaces whose longitudinal direction is along the lateral direction of the second surface, along the longitudinal direction of the second surface.
Sensor element. A long rectangular parallelepiped-shaped element body provided with an oxygen ion conductive solid electrolyte layer,
An outer electrode disposed on the first surface, which is one of the surfaces of the element body,
A protective layer which covers at least a part of a second surface of the element body opposite to the first surface, and which has one or more exposed spaces where the second surface is exposed;
Equipped with
The protective layer is a porous body having a plurality of pores,
The one or more exposed spaces are spaces different from the pores, and each volume is 12500 μm ³ or more,
At least one of the exposed spaces has a shape in which the exposed space tends to become narrower as the distance from the second surface increases,
Sensor element. A long rectangular parallelepiped-shaped element body provided with an oxygen ion conductive solid electrolyte layer,
An outer electrode disposed on the first surface, which is one of the surfaces of the element body,
A protective layer which covers at least a part of a second surface of the element body opposite to the first surface, and which has one or more exposed spaces where the second surface is exposed;
Equipped with
The protective layer is a porous body having a plurality of pores,
The one or more exposed spaces are spaces different from the pores, and each volume is 12500 μm ³ or more,
At least one of the exposed spaces has at least two inner surfaces inclined in a direction in which the exposed spaces approach each other with increasing distance from the second surface,
Sensor element. A long rectangular parallelepiped-shaped element body provided with an oxygen ion conductive solid electrolyte layer,
An outer electrode disposed on the first surface, which is one of the surfaces of the element body,
A protective layer which covers at least a part of a second surface of the element body opposite to the first surface, and which has one or more exposed spaces where the second surface is exposed;
Equipped with
The protective layer is a porous body having a plurality of pores,
The one or more exposed spaces are spaces different from the pores, and each volume is 12500 μm ³ or more,
At least one of the exposed spaces has a curved surface in which an inner surface facing the second surface is curved outward.
Sensor element. The protective layer has a plurality of exposed spaces whose longitudinal direction is along the longitudinal direction of the second surface, along the lateral direction of the second surface.
The sensor element according to claim 1 . At least one of the exposed spaces is located so as to overlap the center of a region of the second surface covered with the protective layer when viewed in a direction perpendicular to the second surface,
The sensor element according to any one of claims 1 to 8 . The protective layer has, for at least one of the exposed spaces, one or more columnar portions that support the exposed space in a direction perpendicular to the second surface,
A sensor element according to any one of claims 1-9. The protective layer has a plurality of columnar portions,
When viewed from a direction perpendicular to the second surface, the plurality of columnar parts tend to have a higher density as they are farther from the center of the region of the second surface covered with the protective layer. Has been placed,
The sensor element according to claim 10 . The protective layer has a plurality of columnar portions,
When viewed from a direction perpendicular to the second surface, the plurality of pillars tend to have a higher density as the pillars are closer to the center of the region of the second surface covered with the protective layer. Has been placed,
The sensor element according to claim 10 . The protective layer has a plurality of first exposed spaces whose longitudinal direction is the exposed spaces along the longitudinal direction of the second surface, along the lateral direction of the second surface, and the longitudinal direction. Has a plurality of second exposure spaces that are the exposure spaces that are along the lateral direction of the second surface and intersect the first exposure space, along the longitudinal direction of the second surface,
A sensor element according to any one of claims 1 to 12.   A gas sensor comprising the sensor element according to claim 1.

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