Gas sensor and sensor element

Abstract

To inhibit conduction failure between a connector electrode and a contact bracket while inhibiting a lead from wearing.SOLUTION: A gas sensor comprises a sensor element 20 and a contact bracket 52b. The sensor element 20 includes: an element body 60 with an oxygen ion conductive solid electrolyte layer; an upper connector electrode 71b disposed outside the element body 60; a lead 75b disposed outside the element body 60 and electrically conducted to the upper connector electrode 71b; and a first protective layer 91 covering the lead 75b, in which a thickness T1 of a portion for covering the lead 75b is 2 μm or more, porosity P1 is 20% or less, and an elevation difference D1 from the upper connector electrode 71b is 22 μm or less. The contact bracket 52b includes: a conduction part 53c projecting toward the upper connector electrode 71b and brought into contact with and electrically conducted to the upper connector electrode 71b; and a support part 53b projecting toward the lead 75b and brought into contact with the first protective layer 91.SELECTED DRAWING: Figure 10

Description

[Technical field]

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

[0002] Conventionally, gas sensors that detect the concentration of a specific gas such as NOx in a measurement gas such as an automobile exhaust gas are known. For example, the gas sensor of Patent Document 1 includes a sensor element and a contact metal that is electrically connected to an electrode provided on the surface of the sensor element. The contact metal is a long and thin member made by bending a metal, and includes a support part and a conductive part that protrude toward the sensor element. When the contact metal is pressed toward the sensor element, the support part contacts the surface of the sensor element and the conductive part contacts the electrode of the sensor element. As a result, the conductive part maintains electrical continuity between the sensor element and the contact member, and the support part also contacts the sensor element, preventing the sensor element from cracking due to the pressing force from the conductive part. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-209104 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when leads are connected to the electrodes of the sensor element, and the leads are arranged on the outside of the sensor element, the leads may come into contact with the support parts of the contact fittings and become worn due to friction. In order to prevent this, it is conceivable to cover the leads with a protective layer to prevent direct contact between the leads and the support parts. However, when the leads are covered with a protective layer, the thickness of the protective layer may result in insufficient conduction between the conductive parts and the electrodes.

[0005] The present invention has been made to solve these problems, and has as its main object to suppress poor electrical continuity between connector electrodes and contact fittings while suppressing wear on the leads. [Means for solving the problem]

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

[0007] The gas sensor of the present invention comprises: A gas sensor for detecting a specific gas concentration in a measurement gas, comprising: An element body having an oxygen ion conductive solid electrolyte layer; a connector electrode disposed on the outside of the element body; a lead disposed on the outside of the element body and electrically connected to the connector electrode; a protective layer covering the lead, the thickness T1 of the portion covering the lead being 2 μm or more, the porosity P1 being 20% ​​or less, and the height difference D1 between the protective layer and the connector electrode being 22 μm or less; A sensor element having a contact metal fitting having a conductive portion that protrudes toward the connector electrode and is in contact with the connector electrode to be electrically conductive, and a support portion that protrudes toward the lead and is in contact with the protective layer; It is equipped with the following:

[0008] In this gas sensor, the protective layer between the lead and the support has a porosity P1 of 20% or less and a thickness T1 of the protective layer covering the lead is 2 μm or more, so that the protective layer protects the lead from the support and suppresses wear of the lead. In addition, the greater the thickness T1, the greater the height difference D1 between the protective layer and the connector electrode tends to be. However, by setting the height difference D1 to 22 μm or less, the height of the protective layer is too large compared to the height of the connector electrode, which causes insufficient contact between the conductive part and the connector electrode and suppresses poor conduction between the conductive part and the connector electrode. From the above, the gas sensor of the present invention can suppress poor conduction between the connector electrode and the contact metal while suppressing wear of the lead. Here, the height difference D1 is a positive value when the height of the protective layer is greater than the height of the connector electrode. In other words, the height difference D1 is a value obtained by subtracting the height of the connector electrode from the height of the protective layer.

[0009] In the gas sensor of the present invention, the porosity P1 of the protective layer may be 10% or less, thereby enhancing the effect of the protective layer in suppressing wear of the leads.

[0010] In the gas sensor of the present invention, the element body may have an elongated shape having a longitudinal direction, the conductive portion and the support portion of the contact fitting may be arranged along the longitudinal direction, and the length L of the protective layer in the longitudinal direction may be 2 mm or more. In this way, even if the relative positions of the protective layer and the support portion are shifted in the longitudinal direction, the protective layer is likely to remain between the support portion and the lead and protect the lead. This makes it possible to prevent the support portion from coming into direct contact with the lead and causing wear on the lead.

[0011] In the gas sensor of the present invention, the height difference D2 obtained by subtracting the height of the connector electrode from the height of the lead may exceed 0 μm. If the height difference D2 exceeds 0 μm, that is, if the lead is taller than the connector electrode, the height difference D1 is likely to be large because of the presence of an additional protective layer on the lead. Even in this case, however, by keeping the height difference D1 at 22 μm or less, poor electrical connection between the connector electrode and the contact fitting can be suppressed.

[0012] In the gas sensor of the present invention, the height difference D1 may be 4 μm or more.In the gas sensor of the present invention, the protective layer may be made of ceramics containing particles of at least one of alumina and zirconia.

[0013] The sensor element of the present invention comprises: A sensor element for detecting a specific gas concentration in a measurement gas, comprising: An element body having an oxygen ion conductive solid electrolyte layer; a connector electrode disposed on the outside of the element body; a lead disposed on the outside of the element body and electrically connected to the connector electrode; a protective layer covering the lead, the thickness T1 of the portion covering the lead being 2 μm or more, the porosity P1 being 20% ​​or less, and the height difference D1 between the protective layer and the connector electrode being 22 μm or less; It is equipped with the following:

[0014] This sensor element, like the sensor element of the gas sensor described above, has a protective layer with a porosity P1 of 20% or less, a thickness T1 of the portion covering the lead of 2 μm or more, and a height difference D1 between the protective layer and the connector electrode of 22 μm or less. Therefore, this sensor element is suitable for use in the gas sensor of the present invention described above. For example, when attaching a contact metal fitting to this sensor element, if the conductive portion of the contact metal fitting is conductive with the connector electrode and the support portion of the contact metal fitting is in contact with the portion of the protective layer covering the lead, it is possible to suppress wear of the lead while suppressing poor conductivity between the connector electrode and the contact metal fitting. Note that various aspects of the gas sensor of the present invention described above may be adopted in this sensor element. [Brief description of the drawings]

[0015] [Figure 1] FIG. 4 is a vertical cross-sectional view showing a state in which the gas sensor 10 is attached to a pipe 58. [Diagram 2] FIG. [Diagram 3] Cross section AA of Figure 2. [Figure 4] FIG. [Diagram 5] FIG. [Figure 6] Cross-sectional view taken along line B-B in FIG. 5 . [Figure 7] FIG. [Figure 8] 5 is an explanatory diagram showing contact portions C1, C2 between the sensor element 20 and a contact metal fitting 52. FIG. [Figure 9] FIG. 9 is a partially enlarged view of cross section CC of FIG. 8. [Figure 10] A partially enlarged view of the DD cross section of Figure 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Next, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a vertical cross-sectional view showing a state in which a gas sensor 10 according to an embodiment of the present invention is attached to a pipe 58. Fig. 2 is a perspective view of a sensor element 20 as viewed from the upper right front. Fig. 3 is a cross-sectional view taken along line AA in Fig. 2. Fig. 4 is a top view of the sensor element 20. In this embodiment, as shown in Figs. 2 and 3, the longitudinal direction of an element body 60 of the sensor element 20 is defined as a front-rear direction (length direction), the layering direction (thickness direction) of the element body 60 is defined as a top-down direction, and the direction perpendicular to the front-rear direction and the top-down direction is defined as a left-right direction (width direction).

[0017] 1, the gas sensor 10 includes an assembly 15, a bolt 47, an outer cylinder 48, a connector 50, lead wires 55, and a rubber plug 57. The assembly 15 includes a sensor element 20, a protective cover 30, and an element sealing body 40. The gas sensor 10 is attached to a pipe 58, such as an exhaust gas pipe of a vehicle, and detects NOx and O contained in exhaust gas as a gas to be measured. 2 The gas sensor 10 is used to measure the concentration of a specific gas (specific gas concentration) such as NOx. In this embodiment, the gas sensor 10 measures the NOx concentration as the specific gas concentration. Of the two ends (front end and rear end) along the longitudinal direction of the sensor element 20, the front end side is the side exposed to the measured gas.

[0018] 1, the protective cover 30 includes a cylindrical inner protective cover 31 with a bottom that covers the front end side of the sensor element 20, and a cylindrical outer protective cover 32 with a bottom that covers the inner protective cover 31. A plurality of holes are formed in each of the inner and outer protective covers 31, 32 for passing the gas to be measured. An element chamber 33 is formed as a space surrounded by the inner protective cover 31, and a fifth surface 60e (front end surface) of the sensor element 20 is disposed within the element chamber 33.

[0019] The element encapsulation body 40 is a member that encapsulates and fixes the sensor element 20. The element encapsulation body 40 includes a cylindrical body 41 having a metal shell 42 and an inner cylinder 43, insulators 44a to 44c, powder compacts 45a and 45b, and a metal ring 46. The sensor element 20 is located on the central axis of the element encapsulation body 40 and penetrates the element encapsulation body 40 in the vertical direction.

[0020] The metal shell 42 is a cylindrical metal member. The front side of the metal shell 42 is a thick portion 42a whose inner diameter is smaller than that of the rear side. A protective cover 30 is attached to the same side (front side) of the metal shell 42 as the front end of the sensor element 20. The rear end of the metal shell 42 is welded to a flange portion 43a of the inner cylinder 43. A part of the inner circumferential surface of the thick portion 42a is a bottom surface 42b that is a stepped surface. This bottom surface 42b holds the insulator 44a so that it does not jump out forward.

[0021] The inner cylinder 43 is a cylindrical metal member and has a flange portion 43a at the front end. The inner cylinder 43 and the metal shell 42 are coaxially fixed by welding. The inner cylinder 43 is also formed with a reduced diameter portion 43c for pressing the powder compact 45b in the central axial direction of the inner cylinder 43, and a reduced diameter portion 43d for pressing the insulators 44a to 44c and the powder compacts 45a and 45b downward in FIG. 1 via the metal ring 46.

[0022] The insulators 44a to 44c and the powder compacts 45a, 45b are disposed between the inner circumferential surface of the cylindrical body 41 and the sensor element 20. The insulators 44a to 44c serve as supporters for the powder compacts 45a, 45b. The powder compacts 45a, 45b are formed by molding ceramic powder such as talc. The powder compacts 45a, 45b are filled between the cylindrical body 41 and the sensor element 20 and compressed, whereby the powder compacts 45a, 45b seal the gap between the element chamber 33 in the protective cover 30 and the space 49 in the outer cylinder 48 and fix the sensor element 20.

[0023] Bolt 47 is fixed to the outside of metallic shell 42 coaxially with metallic shell 42. An external thread is formed on the outer circumferential surface of bolt 47. This external thread is inserted into fixing member 59, which is welded to pipe 58 and has an internal thread on its inner circumferential surface. This allows gas sensor 10 to be fixed to pipe 58 with the front end side of sensor element 20 and part of protective cover 30 of gas sensor 10 protruding into pipe 58.

[0024] The outer cylinder 48 is a cylindrical metal member, and covers the inner cylinder 43, the rear end side of the sensor element 20, and the connector 50. The rear part of the metal shell 42 is inserted inside the outer cylinder 48. The front end of the outer cylinder 48 is welded to the metal shell 42. A plurality of lead wires 55 connected to the connector 50 are drawn out from the rear end of the outer cylinder 48 to the outside. The connector 50 is in contact with and electrically connected to an upper connector electrode 71 and a lower connector electrode 72 disposed on the surface of the rear end side of the sensor element 20. Through this connector 50, the lead wires 55 are electrically conducted to each of the electrodes 64 to 68 and the heater 69 inside the sensor element 20. The connector 50 will be described in detail later. The gap between the outer cylinder 48 and the lead wires 55 is sealed by a rubber plug 57. A space 49 inside the outer cylinder 48 is filled with a reference gas. A sixth surface 60f (rear end surface) of the sensor element 20 is disposed in the space 49.

[0025] As shown in Figures 2 to 4, the sensor element 20 includes an element body 60, a detection unit 63, a heater 69, an upper connector electrode 71, a lower connector electrode 72, a porous layer 80, a first dense layer 86, a second dense layer 87, a first protective layer, and a second protective layer. The element body 60 is made of zirconia (ZrO 2 The element body 60 has a laminate in which a plurality of oxygen ion conductive solid electrolyte layers (six in FIG. 3 ) such as oxygen ion conductive solid electrolyte layers are laminated. The element body 60 has an elongated rectangular parallelepiped shape with the longitudinal direction along the front-rear direction, and has first to sixth faces 60a to 60f as outer surfaces on the top, bottom, left, right, front and rear, respectively. The first to fourth faces 60a to 60d are surfaces along the longitudinal direction of the element body 60 and correspond to side faces of the element body 60. The fifth face 60e is the front end face of the element body 60, and the sixth face 60f is the rear end face of the element body 60. The dimensions of the element body 60 may be, for example, a length of 25 mm to 100 mm, a width of 2 mm to 10 mm, and a thickness of 0.5 mm to 5 mm. The element body 60 is formed with a measurement gas inlet 61 that opens to the fifth face 60e and introduces a measurement gas into the element body 60 itself, and a reference gas inlet 62 that opens to the sixth face 60f and introduces a reference gas (here, air) that serves as a standard for detecting a specific gas concentration into the element body 60 itself.

[0026] The detection section 63 is for detecting the concentration of a specific gas in the measurement gas. The detection section 63 has a plurality of electrodes disposed on the front end side of the element body 60. In this embodiment, the detection section 63 includes an outer electrode 64 disposed on the first surface 60a, and an inner main pump electrode 65, an inner auxiliary pump electrode 66, a measurement electrode 67, and a reference electrode 68 disposed inside the element body 60. The inner main pump electrode 65 and the inner auxiliary pump electrode 66 are disposed on the inner circumferential surface of the space inside the element body 60 and have a tunnel-like structure.

[0027] The principle by which the detection unit 63 detects the concentration of a specific gas in a measurement gas is well known and will not be described in detail. However, the detection unit 63 detects the concentration of a specific gas, for example, as follows. The detection unit 63 pumps oxygen in the measurement gas around the inner main pump electrode 65 to the outside (element chamber 33) or pumps oxygen in the measurement gas around the inner main pump electrode 65 based on a voltage applied between the outer electrode 64 and the inner auxiliary pump electrode 65. The detection unit 63 also pumps oxygen in the measurement gas around the inner auxiliary pump electrode 66 to the outside (element chamber 33) based on a voltage applied between the outer electrode 64 and the inner auxiliary pump electrode 66. As a result, the measurement gas, whose oxygen concentration has been adjusted to a predetermined value, reaches the vicinity of the measurement electrode 67. The measurement electrode 67 functions as a NOx reduction catalyst and reduces the specific gas (NOx) in the measurement gas that has reached it. The detection unit 63 generates, as an electric signal, an electromotive force generated between the measurement electrode 67 and the reference electrode 68 in accordance with the oxygen concentration after reduction, or a current flowing between the measurement electrode 67 and the outer electrode 64 based on the electromotive force. The electric signal thus generated by the detection unit 63 is a signal indicating a value in accordance with the specific gas concentration in the measured gas (a value from which the specific gas concentration can be derived), and corresponds to the detection value detected by the detection unit 63.

[0028] The heater 69 is an electric resistor disposed inside the element body 60. When power is supplied from the outside, the heater 69 generates heat to heat the element body 60. The heater 69 heats and keeps warm the solid electrolyte layer that forms the element body 60, and can adjust the temperature to a temperature (e.g., 800° C.) at which the solid electrolyte layer is activated.

[0029] The upper connector electrode 71 and the lower connector electrode 72 are disposed on either rear end side of the side surface of the element body 60, and are electrodes for electrical conduction with the outside. Both the upper and lower connector electrodes 71 and 72 are exposed to the outside of the sensor element 20. In this embodiment, the upper connector electrode 71 includes four upper connector electrodes 71a to 71d arranged along the left-right direction and disposed on the rear end side of the first surface 60a. Similarly, the lower connector electrode 72 includes four electrodes arranged along the left-right direction and disposed on the rear end side of the second surface 60b (lower surface) opposite to the first surface 60a (upper surface). Only a part of the four lower connector electrodes 72 is illustrated in FIGS. 1 to 3. Each of the upper and lower connector electrodes 71 and 72 is electrically connected to either one of the multiple electrodes 64 to 68 and the heater 69 of the detection unit 63. In this embodiment, the upper connector electrode 71a is electrically connected to the measurement electrode 67, the upper connector electrode 71b is electrically connected to the outer electrode 64, the upper connector electrode 71c is electrically connected to the inner auxiliary pump electrode 66, the upper connector electrode 71d is electrically connected to the inner main pump electrode 65, and the four lower connector electrodes 72 are electrically connected to the heater 69 and the reference electrode 68. The upper connector electrode 71b and the outer electrode 64 are electrically connected to each other via a lead 75b arranged on the first surface 60a (see FIGS. 3 and 4). The upper connector electrode 71c and the inner auxiliary pump electrode 66 are electrically connected to each other via a lead 75c (see FIGS. 2 and 4) arranged on the first surface 60a and the fourth surface 60d and a lead arranged inside the element body 60. The other connector electrodes are electrically connected to the corresponding electrodes or the heater 69 via leads, through holes, etc. arranged inside the element body 60.

[0030] The leads 75b, 75c are conductors containing a precious metal such as platinum (Pt) or a high melting point metal such as tungsten (W) or molybdenum (Mo). The leads 75b, 75c are preferably conductors of a cermet containing a precious metal or a high melting point metal and an oxygen ion conductive solid electrolyte (zirconia in this embodiment) contained in the element body 60. In this embodiment, the leads 75b, 75c are conductors of a cermet containing platinum and zirconia. The porosity of the leads 75b, 75c may be, for example, 5% or more and 40% or less. The line width (thickness) of the leads 75b, 75c is, for example, 0.1 mm or more and 1.0 mm or less. An insulating layer (not shown) for insulating the leads 75b, 75c from the solid electrolyte layer of the element body 60 may be disposed between the leads 75b, 75c and the first surface 60a of the element body 60.

[0031] The porous layer 80 is a porous body that covers at least the front end side of the side surfaces, i.e., the first and second faces 60a and 60b, of the element body 60 on which the upper and lower connector electrodes 71 and 72 are disposed. In this embodiment, the porous layer 80 includes an inner porous layer 81 that covers the first and second faces 60a and 60b, respectively, and an outer porous layer 85 that is disposed on the outside of the inner porous layer 81.

[0032] The inner porous layer 81 includes a first inner porous layer 83 that covers the first surface 60a and a second inner porous layer 84 that covers the second surface 60b. The first inner porous layer 83 covers the entire area from the front end of the first surface 60a, where the upper connector electrodes 71a to 71d are arranged, to the first dense layer 86 (see FIGS. 2 to 4). The left-right width of the first inner porous layer 83 is the same as the left-right width of the first surface 60a, and the first inner porous layer 83 covers the first surface 60a from the left end to the right end of the first surface 60a. The first inner porous layer 83 covers at least a part of each of the outer electrode 64 and the lead 75b. The first inner porous layer 83 plays a role of protecting the outer electrode 64 and the lead 75b from components such as sulfuric acid in the measurement gas in the element chamber 33, for example, and suppressing corrosion of these. The second inner porous layer 84 covers the entire area from the front end of the second surface 60b, where the lower connector electrode 72 is disposed, to the second dense layer 87 (see FIGS. 2 and 3). The second inner porous layer 84 is disposed symmetrically to the first inner porous layer 83 in the vertical direction.

[0033] The outer porous layer 85 covers the first to fifth faces 60a to 60e. The outer porous layer 85 covers the first face 60a and the second face 60b by covering the inner porous layer 81. The outer porous layer 85 has a shorter length in the front-rear direction than the inner porous layer 81, and unlike the inner porous layer 81, covers only the front end and the region near the front end of the element body 60. As a result, the outer porous layer 85 covers the peripheral parts of the electrodes 64 to 68 of the detection section 63 of the element body 60, in other words, the parts of the element body 60 that are disposed in the element chamber 33 and exposed to the measured gas. As a result, the outer porous layer 85 plays a role in suppressing the occurrence of cracks in the element body 60 due to the adhesion of moisture in the measured gas, for example.

[0034] The porous layer 80 has a porosity of 10% or more. The porous layer 80 covers the outer electrode 64 and the measurement gas inlet 61, and if the porosity is 10% or more, the measurement gas can pass through the porous layer 80. The porosity of the inner porous layer 81 may be 10% or more and 50% or less. The porosity of the outer porous layer 85 may be 10% or more and 85% or less. The outer porous layer 85 may have a higher porosity than the inner porous layer 81.

[0035] The first dense layer 86 and the second dense layer 87 suppress the capillary phenomenon of water along the longitudinal direction of the element body 60. The first dense layer 86 is disposed on the first surface 60a on which the upper connector electrode 71 and the first inner porous layer 83 are disposed. The first dense layer 86 is disposed behind the outer electrode 64 and ahead of the first protective layer 91. The first dense layer 86 is disposed behind all of the multiple electrodes 64 to 68 of the detection unit 63 including the outer electrode 64 (see FIG. 3). The first dense layer 86 is disposed at a position overlapping with the insulator 44b in the front-rear direction (see FIG. 1). In other words, the region from the front end to the rear end of the first dense layer 86 is located within the region from the front end to the rear end of the insulator 44b. When moisture moves backward in the first inner porous layer 83 by capillary action, the first dense layer 86 serves to prevent the moisture from passing through the first dense layer 86 and thus prevent the moisture from reaching the upper connector electrode 71. The first dense layer 86 is a dense layer with a porosity of less than 10%. The left-right width of the first dense layer 86 is the same as the left-right width of the first surface 60a, and the first dense layer 86 covers the first surface 60a from the left end to the right end of the first surface 60a. The first dense layer 86 is adjacent to the rear end of the first inner porous layer 83. The first dense layer 86 is disposed apart from the first protective layer 91. As shown in FIG. 4, the first dense layer 86 covers a part of the lead 75b. Between the first dense layer 86 and the first protective layer 91, there is a gap region in which the porous layer 80 and the first protective layer 91 are not present, and the lead 75b is exposed in the gap region.

[0036] The second dense layer 87 is disposed on the second surface 60b on which the lower connector electrode 72 and the second inner porous layer 84 are disposed. The second dense layer 87 is disposed so as to be vertically symmetrical with the first dense layer 86, and therefore a detailed description of the arrangement of the second dense layer 87 will be omitted. When moisture moves backward through the second inner porous layer 84 by capillary action, the second dense layer 87 serves to prevent the moisture from passing through the second dense layer 87 and thus preventing the moisture from reaching the lower connector electrode 72. The second dense layer 87 is a dense layer with a porosity of less than 10%.

[0037] The first dense layer 86 and the second dense layer 87 each preferably have a longitudinal length of 0.5 mm or more. A length of 0.5 mm or more can adequately prevent moisture from passing through the first dense layer 86 and the second dense layer 87. The lengths of the first dense layer 86 and the second dense layer 87 may be 25 mm or less, or may be 20 mm or less. Note that, although the length of the first dense layer 86 and the length of the second dense layer 87 are the same in this embodiment, they may be different values.

[0038] The first protective layer 91 is a member for protecting the leads 75b, 75c from the contact fittings 52 of the connector 50. The first protective layer 91 is disposed on the first surface 60a on which the upper connector electrode 71 and the leads 75b, 75c are disposed. The first protective layer 91 covers at least a part of the leads 75b, 75c formed on the first surface 60a. The first protective layer 91 is disposed behind the first dense layer 86 and in front of the upper connector electrode 71. The first protective layer 91 is disposed behind the insulator 44c (see FIG. 1). The left-right width of the first protective layer 91 is the same as the left-right width of the first surface 60a, and the first protective layer 91 covers the first surface 60a from the left end to the right end of the first surface 60a. The first protective layer 91 is disposed adjacent to the rear end of the upper connector electrode 71 or at a position slightly forwardly spaced from the upper connector electrode 71. The first protective layer 91 has a porosity P1 of 20% or less. The porosity P1 is preferably 10% or less. The porosity P1 may be lower than the porosity of the porous layer 80.

[0039] The second protective layer 92 is disposed on the second surface 60b on which the lower connector electrodes 72 are disposed. The second protective layer 92 is disposed so as to be vertically symmetrical with the first protective layer 91. In this embodiment, since no leads are disposed on the surface of the second surface 60b, the second protective layer 92 does not cover the leads. The second protective layer 92 serves to protect the second surface 60b.

[0040] The connector 50 will be described in detail. FIG. 5 is a perspective view of the connector 50. FIG. 6 is a cross-sectional view taken along line BB of FIG. 5. FIG. 7 is a perspective view of the contact metal fitting 52. FIG. 8 is an explanatory diagram showing contact portions C1 and C2 between the sensor element 20 and the contact metal fitting 52. FIG. 6 shows a cross section passing through the upper connector electrode 71b of the sensor element 20. Also, the lead 75b is omitted from FIG. 6. FIG. 8 shows an enlarged view of the periphery of the first protective layer 91 in FIG. 4. The connector 50 includes a first housing 51a and a second housing 51b, a contact metal fitting 52, and a clamp 54.

[0041] The first housing 51a and the second housing 51b are members made of ceramics such as sintered alumina. The first housing 51a and the second housing 51b each hold a plurality of (four in this example) contact fittings 52 arranged in a direction (left-right direction) perpendicular to the longitudinal direction of the sensor element 20.

[0042] The contact metal fitting 52 is a member made by bending a plate-shaped metal, for example. The contact metal fitting 52 includes a tip portion 53a, a support portion 53b, a conductive portion 53c, a hook portion 53d, and a holding portion 53e. The tip portion 53a and the hook portion 53d have a curved shape, and are engaged with the first and second housings 51a and 51b to hold the contact metal fitting 52 in the first and second housings 51a and 51b (see FIG. 6). The support portion 53b and the conductive portion 53c are arranged along the longitudinal direction of the contact metal fitting 52, and the conductive portion 53c is arranged closer to the holding portion 53e than the support portion 53b. Both the support portion 53b and the conductive portion 53c are curved and protrude toward the sensor element 20. The holding portion 53e crimps and holds the multiple core wires of the lead wire 55 outside the connector 50. Incidentally, the holding portion 53e in FIG. 7 shows the state before being crimped.

[0043] The support portion 53b and the conductive portion 53c of the contact fitting 52 are both formed to be elastically deformable, and have a spring constant in the range of, for example, 500 to 4000 N / mm. As shown in FIG. 7, the support portion 53b projects toward the sensor element 20 by a protruding height H1. The conductive portion 53c projects toward the sensor element 20 by a protruding height H2. It is preferable that the protruding height H2 of the conductive portion 53c is 90% to 110% of the protruding height H1. It is preferable that the protruding height H1 and the protruding height H2 are as close as possible, and it is more preferable that the protruding height H1 and the protruding height H2 are equal. Note that "the protruding height H1 and the protruding height H2 are equal" includes the case where the protruding heights are approximately equal. The protruding heights H1 and H2 are not particularly limited, but are, for example, 0.1 mm to 1 mm. The support portion 53b has a radius of curvature R1 of the inner peripheral surface of the tip portion of the protruding shape (the upper surface of the support portion 53b in FIG. 7) of 0.8 to 1.6 mm, for example, and the radius of curvature R2, R3 of the outer peripheral surface of the curved shoulder portions of the protruding shape (the upper surface in FIG. 7) of 1.2 mm to 2.2 mm, for example. The conductive portion 53c has a radius of curvature R4 of the inner peripheral surface of the tip portion of the protruding shape (the upper surface of the conductive portion 53c in FIG. 7) of 0.8 to 1.6 mm, for example, and the radius of curvature R5, R6 of the outer peripheral surface of the curved shoulder portions of the protruding shape (the upper surface in FIG. 7) of 1.2 mm to 1.5 mm, for example. The radius of curvature R2 may be equal to R3, or the radius of curvature R5 may be equal to R6. The radii of curvature R5, R6 may be the same as the radii of curvature R2, R3, or may be larger than the radii of curvature R2, R3. The values ​​of the protrusion height H1, protrusion height H2, and curvature radii R1 to R6 described here are all values ​​when the connector 50 is attached to the sensor element 20 (the contact metal fitting 52 is in contact with the sensor element 20).

[0044] The contact metal fittings 52 are held by the first and second housings 51a and 51b such that the conductive portions 53c of each of the contact metal fittings 52 face the upper connector electrodes 71 and the lower connector electrodes 72 of the sensor element 20 in a one-to-one correspondence. As a result, the conductive portions 53c of each of the contact metal fittings 52 come into contact with the opposing upper connector electrodes 71 and lower connector electrodes 72, and are electrically connected thereto. The support portions 53b of each of the contact metal fittings 52 come into contact with the sensor element 20 at a position forward of the upper connector electrodes 71 and lower connector electrodes 72 of the sensor element 20, and more specifically, come into contact with the first protective layer 91 and the second protective layer 92 of the sensor element 20. In FIG. 8, the positions of the contact portions C1 between the support portions 53b and the first protective layer 91 and the positions of the contact portions C2 between the conductive portions 53c and the upper connector electrodes 71 are indicated by dashed lines. The positions of the contact parts between the contact metal fittings 52 and the lower connector electrodes 72 and second protective layer 92 are the same as those in FIG. 8 and therefore are not shown.

[0045] Among the multiple contact fittings 52, those held by the first housing 51a and in contact with the upper connector electrodes 71a to 71d are referred to as contact fittings 52a to 52d to be distinguished (see FIG. 5). For example, the conductive portion 53c of the contact fitting 52b contacts the upper connector electrode 71b at the contact portion C2 shown in FIG. 8, and the support portion 53b of the contact fitting 52b contacts the first protective layer 91 at the contact portion C1 forward of the upper connector electrode 71b. The conductive portion 53c of the contact fitting 52c contacts the upper connector electrode 71c at the contact portion C2 shown in FIG. 8, and the support portion 53b of the contact fitting 52c contacts the first protective layer 91 at the contact portion C1 forward of the upper connector electrode 71c. As shown in FIG. 8, a lead 75b is present directly below the contact portion C1 between the support portion 53b of the contact fitting 52b and the first protective layer 91. Directly below the contact portion C1 between the support portion 53b of the contact metal fitting 52c and the first protective layer 91, there is a lead 75c.

[0046] The clamp 54 is a plate-shaped metal bent into a C-shape, and has an elastic force capable of clamping the first housing 51a and the second housing 51b and pressing them in a direction toward each other. The clamp 54 holds the first housing 51a and the second housing 51b by this elastic force. In addition, the support portion 53b and the conductive portion 53c of the contact metal fitting 52 are elastically deformed by the pressing force from the clamp 54, and clamp and fix the sensor element 20. The connector 50 can teach and fix the sensor element 20 by the pressing force due to the elastic deformation of the support portion 53b and the conductive portion 53c. In addition, since the conductive portion 53c is elastically deformed, electrical conduction between the conductive portion 53c and the upper connector electrode 71 and the lower connector electrode 72 can be maintained.

[0047] Here, the positional relationship between the upper connector electrode 71b, the lead 75b, the first protective layer 91, and the contact metal fitting 52b will be described in detail. FIG. 9 is a partial enlarged view of the CC cross section of FIG. 8. FIG. 10 is a partial enlarged view of the DD cross section of FIG. 8. For convenience of explanation, in FIG. 10, the height differences D1 and D2 described later are exaggerated. As shown in FIGS. 9 and 10, the first protective layer 91 covers the lead 75b, and is present between the lead 75b and the support part 53b of the contact metal fitting 52b located directly above it, and thus the first protective layer 91 protects the lead 75b from the support part 53b. The thickness T1 of the part of the first protective layer 91 covering the lead 75b is 2 μm or more. The thickness T1 is the thickness of the part of the first protective layer 91 directly above the lead 75b. As described above, the porosity P1 of the first protective layer 91 is 20% or less. In this way, the porosity P1 of the first protective layer 91 present between the lead 75b and the support portion 53b is 20% or less and the thickness T1 is 2 μm or more, so that the first protective layer 91 protects the lead 75b from the support portion 53b and suppresses wear of the lead 75b. In addition, the height difference D1 (see FIG. 10) between the upper connector electrode 71b connected to the lead 75b and the first protective layer 91 is 22 μm or less. Here, if the height difference D1 is too large, that is, if the height of the first protective layer 91 (here, the height of the upper surface of the first protective layer 91) is too large compared to the height of the upper connector electrode 71b (here, the height of the upper surface of the upper connector electrode 71b), the contact at the contact portion C2 between the conductive portion 53c of the contact metal fitting 52b and the upper connector electrode 71b may be insufficient. This may make it easier for poor conduction between the conductive portion 53c and the upper connector electrode 71b to occur. By setting the height difference D1 to 22 μm or less, the occurrence of such a conduction failure can be suppressed. From the above, in the gas sensor 10 of this embodiment, by setting the thickness T1 of the first protective layer 91 to 2 μm or more, the porosity P1 to 20% or less, and the height difference D1 to 22 μm or less, it is possible to suppress wear of the lead 75b while suppressing conduction failure between the upper connector electrode 71b and the contact metal fitting 52b. The greater the thickness T1, the greater the effect of suppressing wear of the lead 75b, but the greater the thickness T1, the greater the height difference D1 tends to be.In the gas sensor 10 of this embodiment, the thickness T1 is set to 2 μm or more, while the height difference D1 is set to 22 μm or less, thereby achieving both the suppression of wear and the suppression of poor conduction. Note that the height difference D1 is a positive value when the height of the first protective layer 91 is greater than the height of the upper connector electrode 71b. In other words, the height difference D1 is a value obtained by subtracting the height of the upper connector electrode 71b from the height of the first protective layer 91. The height difference D1 may be greater than 0 μm, or may be 4 μm or more.

[0048] In this embodiment, the height difference D2 (see FIG. 10) obtained by subtracting the height of the upper connector electrode 71b from the height of the lead 75b exceeds 0 μm. That is, the height of the lead 75b is greater than the height of the upper connector electrode 71b. In this embodiment, as shown in FIG. 10, the thickness T2 of the lead 75b is greater than the thickness T3 of the upper connector electrode 71b, so that the height difference D2 exceeds 0 μm. Here, the height difference D1 is the sum of the height difference D2 and the thickness T1 of the first protective layer 91. Therefore, when the height difference D2 exceeds 0 μm, that is, is a positive value, the height difference D1 cannot be set to 0 μm and always exceeds 0 μm (a positive value). Even in this case, if the height difference D1 is 22 μm or less, the conduction failure between the conductive portion 53c of the contact metal fitting 52b and the upper connector electrode 71b can be suppressed for the above-mentioned reason. The height difference D2 may be 2 μm or more. When thickness T2>thickness T3, a part of lead 75b may cover the front end of upper connector electrode 71b. That is, lead 75b and upper connector electrode 71b may partially overlap. In this way, electrical continuity between lead 75b and upper connector electrode 71b can be more reliably established.

[0049] The porosity P1 of the first protective layer 91 is preferably 10% or less. If the porosity P1 is 10% or less, the first protective layer 91 becomes dense and wear of the first protective layer 91 itself is suppressed at the contact portion C1 between the first protective layer 91 and the support portion 53b. This can suppress the support portion 53b from coming into contact with the lead 75b due to wear of the first protective layer 91, and further suppress wear of the lead 75b.

[0050] The thickness T1 of the first protective layer 91 may be 10 μm or more. The greater the thickness T1, the greater the effect of the first protective layer 91 in suppressing wear of the leads 75b. The thickness T1 may be 20 μm or less.

[0051] The first protective layer 91 preferably has a length L (see Figs. 4 and 10) of 2 mm or more along the longitudinal direction (front-rear direction here) of the sensor element 20. If the length L is 2 mm or more, even if the relative position between the first protective layer 91 and the support portion 53b of the contact metal fitting 52b is shifted in the longitudinal direction, the first protective layer 91 is likely to be present between the support portion 53b and the lead 75b and to maintain a state in which the lead 75b is protected. In other words, the position of the contact portion C1 between the sensor element 20 and the contact metal fitting 52b is unlikely to come out of the first protective layer 91. Therefore, it is possible to prevent the support portion 53b from directly contacting the lead 75b and wearing the lead 75b. The length L may be 6 mm or less. The distance Lg (see Figs. 4 and 10) between the first protective layer 91 and the front end of the upper connector electrode 71 may be, for example, 0 μm or more. In this embodiment, the first protective layer 91 is disposed forward and spaced apart from the upper connector electrode 71, and the distance Lg is a value greater than 0 μm.

[0052] Although the suppression of wear of the lead 75b and the suppression of poor conduction between the upper connector electrode 71b and the contact metal fitting 52b have been described above, the same can be said about the lead 75c and the upper connector electrode 71c. For example, if the thickness T1 of the portion of the first protective layer 91 covering the lead 75c is 2 μm or more, the porosity P1 of the first protective layer 91 is 20% or less, and the height difference D1 between the first protective layer 91 and the upper connector electrode 71c is 22 μm or less, the wear of the lead 75c can be suppressed while the poor conduction between the upper connector electrode 71c and the contact metal fitting 52c can be suppressed. In this way, when there are multiple leads covered by the first protective layer 91, if the above-mentioned conditions of thickness T1, porosity P1, and height difference D1 are satisfied for each lead, the connector electrode connected to the lead, and the first protective layer 91, the wear of the lead can be suppressed and the poor conduction of the connector electrode can be suppressed. In the case where there are a plurality of leads covered by the first protective layer 91, it is sufficient that the above-mentioned conditions of thickness T1, porosity P1, and height difference D1 are satisfied for at least one of the leads and the connector electrode connected to the lead. It is also preferable that the above-mentioned conditions of thickness T1, porosity P1, and height difference D1 are satisfied for each of the leads covered by the first protective layer 91 and the connector electrode connected to the lead. In this embodiment, the lead 75b and the lead 75c have the same thickness, the upper connector electrode 71b and the upper connector electrode 71c have the same thickness, and the thickness T1 of the first protective layer 91 is the same value in the portion covering the lead 75b and the portion covering the lead 75c. Therefore, the gas sensor 10 of this embodiment has the advantages of being able to suppress poor conductivity between the upper connector electrode 71b and the contact fitting 52b while suppressing wear on the lead 75b, and being able to suppress poor conductivity between the upper connector electrode 71c and the contact fitting 52c while suppressing wear on the lead 75c.

[0053] In this embodiment, the first protective layer 91 does not cover the leads connected to the upper connector electrodes 71a, 71d, but it is preferable that the height difference between the first protective layer 91 and each of the upper connector electrodes 71a, 71d is also 22 μm or less. This makes it possible to prevent poor conduction between the contact fittings 52 and the upper connector electrodes 71a, 71d. In this embodiment, the second protective layer 92 does not cover the leads and is therefore not related to the effect of preventing wear of the leads, but it is preferable that the height difference between the second protective layer 92 and the lower connector electrodes 72 is 22 μm or less. This makes it possible to prevent poor conduction between the contact fittings 52 and the lower connector electrodes 72.

[0054] The first protective layer 91 is preferably a ceramic containing ceramic particles as constituent particles, and more preferably contains at least one of alumina, zirconia, spinel, cordierite, titania, and magnesia particles. The first protective layer 91 is further preferably a ceramic containing at least one of alumina and zirconia particles as constituent particles. In this embodiment, the first protective layer 91 is made of a ceramic containing alumina particles. The porous layer 80, the first dense layer 86, the second dense layer 87, and the second protective layer 92 can also be made of the same ceramic as the first protective layer 91. In this embodiment, these are also made of alumina ceramic like the first protective layer 91.

[0055] The porosity P1 of the first protective layer 91 is a value derived as follows using an image (SEM image) obtained by observation using a scanning electron microscope (SEM). First, the sensor element 20 is cut along the thickness direction of the first protective layer 91 so that the cross section of the first protective layer 91 is the observation surface, and the cut surface is filled with resin and polished to obtain an observation sample. Next, the magnification of the SEM is set to 1000 to 10000 times, and an observation surface of the observation sample is photographed to obtain an SEM image of the first protective layer 91. Next, the obtained image is analyzed, and a threshold value is determined from the brightness distribution of the brightness data of the pixels in the image by a discriminant analysis method (Otsu's binarization). After that, each pixel in the image is binarized into an object part and a pore part based on the determined threshold value, and the area of ​​the object part and the area of ​​the pore part are calculated. Then, the ratio of the area of ​​the pore part to the total area (the total area of ​​the object part and the pore part) is derived as the porosity (unit: %). The porosities of the porous layer 80, the first dense layer 86, and the second dense layer 87 are also values ​​derived in a similar manner.

[0056] The thicknesses T1 to T3, the height difference D1, and the height difference D2 are values ​​measured using an SEM image as follows, similar to the porosity P1. For example, when measuring the thicknesses T1 to T3, the height difference D1, and the height difference D2 for the first protective layer 91, the lead 75b, and the upper connector electrode 71b, the measurements are performed as follows. First, a cross section (a cross section along the longitudinal direction of the sensor element) of the first protective layer 91 passing through the center of the upper connector electrode 71b in the short-side direction (here, the left-right direction) of the sensor element is set as an observation surface for capturing an SEM image. Next, based on the brightness data of pixels in the obtained SEM image, the areas in the SEM image where the first protective layer 91, the lead 75b, and the upper connector electrode 71b exist are identified. Then, in the SEM image, the thickness of the first protective layer 91 is measured at three points, the center and both ends along the longitudinal direction of the sensor element, in the portion of the first protective layer 91 covering the lead 75b (the portion directly above the lead 75b), and the average of the thicknesses at these three points is defined as thickness T1. Similarly, in the SEM image, the thickness of the lead 75b is measured at three points, the center and both ends of the portion of the lead 75b covered by the first protective layer 91 (the portion directly below the first protective layer 91), and the average of the thicknesses at these three points is defined as thickness T2. For the upper connector electrode 71b, the average of the thicknesses at the center and both ends in the SEM image is defined as thickness T3. The height difference D2 is measured as the distance in the height direction (here, the vertical direction) between the average value of the height positions of the leads 75b (here, the positions of the upper surfaces of the leads 75b) at the same three measurement points as the measurement points of the thickness T2 in the SEM image and the average value of the height positions of the upper connector electrodes 71b (here, the positions of the upper surfaces of the upper connector electrodes 71b) at the same three measurement points as the measurement points of the thickness T3. The height difference D1 is calculated as the sum of the thickness T1 and the height difference D2.

[0057] A method for manufacturing the gas sensor 10 thus configured will be described below. First, a method for manufacturing the sensor element 20 will be described. When manufacturing the sensor element 20, first, a plurality of (here, six) unfired ceramic green sheets corresponding to the element body 60 are prepared. In each green sheet, notches, through holes, grooves, etc. are provided by punching processing or the like as necessary, and electrodes and wiring patterns are screen-printed. The wiring patterns include patterns of unfired leads that become the leads 75b and 75c after firing. In addition, the unfired porous layers that become the first inner porous layer 83 and the second inner porous layer 84 after firing, the unfired dense layers that become the first dense layer 86 and the second dense layer 87 after firing, the unfired protective layers that become the first protective layer 91 and the second protective layer 92 after firing, and the unfired connector electrodes that become the upper connector electrode 71 and the lower connector electrode 72 after firing are also formed by screen printing on the corresponding surfaces of the first and second surfaces 60a and 60b of the green sheets. Then, the plurality of green sheets are stacked. The stacked green sheets are an unsintered element body that will become an element body after sintering. Then, this unsintered element body is sintered to obtain an element body 60 including leads 75b, 75c, upper connector electrode 71, lower connector electrode 72, first protective layer 91, and second protective layer 92. Next, an outer porous layer 85 is formed by plasma spraying to obtain a sensor element 20.

[0058] The porosity P1 of the first protective layer 91 can be adjusted, for example, by adjusting the amount of pore-forming material contained in the unsintered protective layer. The thickness T1 of the first protective layer 91 can be adjusted, for example, by adjusting the amount of solvent contained in the unsintered protective layer to adjust the viscosity of the unsintered protective layer. The thickness T1 can also be adjusted by the number of times screen printing is performed when forming the unsintered protective layer. The same applies to the adjustment of the thickness T2 of the lead 75b and the thickness T3 of the upper connector electrode 71b. The height differences D1 and D2 can also be adjusted by adjusting these thicknesses T1 to T3. The length L of the first protective layer 91 can be adjusted by the shape of a mask used for screen printing when forming the unsintered protective layer.

[0059] Next, the gas sensor 10 incorporating the sensor element 20 is manufactured. First, the sensor element 20 is inserted axially into the cylindrical body 41, and the insulator 44a, the powder compact 45a, the insulator 44b, the powder compact 45b, the insulator 44c, and the metal ring 46 are arranged in this order between the inner circumferential surface of the cylindrical body 41 and the sensor element 20. Next, the metal ring 46 is pressed to compress the powder compacts 45a and 45b, and in this state, the reduced diameter portions 43c and 43d are formed to manufacture the element sealing body 40, which seals the gap between the inner circumferential surface of the cylindrical body 41 and the sensor element 20. Thereafter, the protective cover 30 is welded to the element sealing body 40, and the bolts 47 are attached to obtain the assembly 15.

[0060] Next, the plurality of (eight here) lead wires 55 are passed through the rubber plug 57, and then the core wires of the lead wires 55 are surrounded and crimped by the holding portion 53e of each of the plurality of (eight here) contact fittings 52, so that the contact fittings 52 and the lead wires 55 are electrically connected to each other. Next, in a state in which four contact fittings 52 are held in each of the first housing 51a and the second housing 51b, the sensor element 20 is sandwiched between the first housing 51a and the second housing 51b, and the first housing 51a and the second housing 51b are sandwiched and fixed by the clamp 54. As a result, each of the plurality of contact fittings 52 is in a state in which the support portion 53b contacts the first protective layer 91 or the second protective layer 92, and the conductive portion 53c contacts the upper connector electrode 71 or the lower connector electrode 72. After the connector 50 is connected to the rear end side of the sensor element 20 in this manner, the outer cylinder 48 is welded and fixed to the main metal shell 42 to obtain the gas sensor 10.

[0061] Next, an example of use of the gas sensor 10 thus constructed will be described below. When the gas sensor 10 is attached to the pipe 58 as shown in FIG. 1 and a measurement gas flows through the pipe 58, the measurement gas flows through the protective cover 30 and flows into the element chamber 33, and the front end side of the sensor element 20 is exposed to the measurement gas. When the measurement gas passes through the porous layer 80 and reaches the outer electrode 64 and also reaches the sensor element 20 from the measurement gas inlet 61, the detection unit 63 generates an electric signal corresponding to the NOx concentration in the measurement gas, as described above. This electric signal is extracted via the upper and lower connector electrodes 71 and 72, and the NOx concentration is detected based on the electric signal.

[0062] Here, the correspondence between the components of this embodiment and the components of the present invention will be clarified. The element body 60 of this embodiment corresponds to the element body of the present invention, the upper connector electrode 71b corresponds to the connector electrode, the lead 75b corresponds to the lead, the first protective layer 91 corresponds to the protective layer, and the contact metal fitting 52b corresponds to the contact metal fitting.

[0063] According to the gas sensor 10 of the present embodiment described above, the thickness T1 of the first protective layer 91 is 2 μm or more, the porosity P1 is 20% or less, and the height difference D1 is 22 μm or less, so that it is possible to suppress wear of the lead 75b while suppressing poor conduction between the upper connector electrode 71b and the contact metal fitting 52b. When the lead 75b wears, the resistance value of the lead 75b changes, which may change the electrical signal extracted from the sensor element 20 and reduce the detection accuracy of the specific gas concentration. Furthermore, when the lead 75b wears, the lead 75b may break. By suppressing wear of the lead 75b, it is possible to suppress such a decrease in detection accuracy and breakage.

[0064] Furthermore, by setting the porosity P1 of the first protective layer 91 to 10% or less, the effect of the first protective layer 91 in suppressing wear of the leads 75b is enhanced.

[0065] Furthermore, the element body 60 has an elongated shape having a longitudinal direction, the support portion 53b and the conductive portion 53c of the contact fitting 52b are arranged along the longitudinal direction of the element body 60, and the length L of the first protective layer 91 in this longitudinal direction is 2 mm or more. Since the length L is 2 mm or more, even if the relative position between the first protective layer 91 and the support portion 53b is shifted in the longitudinal direction, the first protective layer 91 is likely to be present between the support portion 53b and the lead 75b and protect the lead 75b. Therefore, it is possible to prevent the support portion 53b from directly contacting the lead 75b and causing wear on the lead 75b. Examples of cases in which the relative position between the first protective layer 91 and the support portion 53b is shifted in the longitudinal direction include a case in which a manufacturing error occurs such that the connection position of the connector 50 is shifted when the connector 50 is connected to the sensor element 20 during the manufacture of the gas sensor 10, and a case in which the gas sensor 10 vibrates due to the vibration of the vehicle during use of the gas sensor 10.

[0066] Furthermore, the height difference D2 obtained by subtracting the height of the upper connector electrode 71b from the height of the lead 75b exceeds 0 μm. When the height difference D2 exceeds 0 μm, that is, when the lead 75b is taller than the upper connector electrode 71b, the presence of the first protective layer 91 on the lead 75b tends to increase the height difference D1. Even in such a case, by keeping the height difference D1 at 22 μm or less, poor electrical connection between the upper connector electrode 71b and the contact fitting 52b can be suppressed.

[0067] It goes without saying that the present invention is not limited to the above-described embodiment, and can be embodied in various forms within the technical scope of the present invention.

[0068] For example, in the above-described embodiment, the first protective layer 91 covers the leads 75b and 75c, but this is not limited thereto. The first protective layer 91 only needs to cover at least one lead. The first protective layer 91 may cover three or more leads.

[0069] In the above-described embodiment, the left and right width of the first protective layer 91 is the same as the left and right width of the first surface 60a, but as long as the first protective layer 91 covers at least one lead, the left and right width of the first protective layer 91 may be smaller than the left and right width of the first surface 60a.

[0070] In the above-mentioned embodiment, the height difference D2 exceeds 0 μm, but is not limited thereto. The height difference D2 may be 0 μm or less than 0 μm (negative value). For example, the height difference D2 may be a negative value because the thickness T2 of the lead 75b is smaller than the thickness T3 of the upper connector electrode 71b. The height difference D2 may be -5 μm or more, or may be 0 μm or more. Also, in the above-mentioned embodiment, the height difference D2 is a positive value because the thickness T2 is greater than the thickness T3, but is not limited thereto. For example, the height difference D2 may be a positive value because another layer exists between the lead 75b and the element body 60, so that the thickness T2 is less than the thickness T3.

[0071] In the above-described embodiment, the height difference D1 exceeds 0 μm, but is not limited to this. The height difference D1 may be 0 μm or less than 0 μm (a negative value). For example, if the sum of the thickness T1 of the first protective layer 91 and the thickness T2 of the lead 75b is less than the thickness T3 of the upper connector electrode 71b, the height difference D1 can be less than 0 μm. The height difference D1 may be -22 μm or more, -10 μm or more, or 0 μm or more.

[0072] In the above-described embodiment, the gas sensor 10 detects the NOx concentration as the specific gas concentration, but the specific gas concentration is not limited to this, and other oxide concentrations may be used as the specific gas concentration. When the specific gas is an oxide, oxygen is generated when the specific gas itself is reduced around the measurement electrode 67 as in the above-described embodiment, so that the specific gas concentration can be detected based on the detection value of the detection unit 63 corresponding to this oxygen. The specific gas may also be a non-oxide such as ammonia. When the specific gas is a non-oxide, the specific gas is converted to an oxide around the inner main pump electrode 65 (for example, ammonia is oxidized and converted to NO), and oxygen is generated when the converted oxide is reduced around the measurement electrode 67, so that the specific gas concentration can be detected based on the detection value of the detection unit 63 corresponding to this oxygen. In this way, whether the specific gas is an oxide or a non-oxide, the gas sensor 10 can detect the specific gas concentration based on the oxygen generated around the measurement electrode 67 derived from the specific gas. EXAMPLES

[0073] Specific examples of gas sensors that have been fabricated will be described below as examples. Experimental Examples 2 to 9, 12, and 13 correspond to examples of the present invention, and Experimental Examples 1, 10, 11, and 14 correspond to comparative examples. Note that the present invention is not limited to the following examples.

[0074] [Experimental Example 1] A gas sensor similar to the gas sensor 10 shown in Figs. 1 to 10 was produced by the above-mentioned production method, except that the first protective layer 91 was not provided, and was used as Experimental Example 1. The sensor element 20 of Experimental Example 1 was produced as follows. First, six ceramic green sheets were prepared by mixing zirconia particles to which 4 mol% of yttria as a stabilizer was added, an organic binder, and an organic solvent, and forming the mixture by tape casting. Patterns of electrodes and the like were formed on each green sheet by screen printing. The formed patterns included a pattern of unfired leads that would become the leads 75b and 75c after firing, and a pattern of an unfired connector electrode that would become the upper connector electrode 71 after firing. The pattern of the unfired leads was formed using a slurry in which platinum particles, zirconia particles, and a solvent were kneaded. The pattern of the unfired connector electrode was formed using a slurry in which platinum particles, zirconia particles, and a solvent were kneaded. Then, the six green sheets were stacked and fired. Thus, the sensor element 20 including the leads 75b, 75c and the upper connector electrode 71 was produced. Next, the assembly 15 incorporating the sensor element 20 was produced, and the connector 50 was connected to the sensor element 20 to conduct the conductive portion 53c of each of the eight contact metal fittings 52 to the upper connector electrode 71 or the lower connector electrode 72. Then, the outer tube 48 was welded to the metal shell 42 to produce the gas sensor 10 of Experimental Example 1. Since the sensor element 20 of Experimental Example 1 does not include the first protective layer 91, the support portion 53b of the contact metal fitting 52b is in direct contact with the lead 75b, and the support portion 53b of the contact metal fitting 52c is in direct contact with the lead 75c. In the sensor element 20 of Experimental Example 1, the thickness T2 of the lead 75b was 12 μm, the thickness T3 of the upper connector electrode 71b was 10 μm, and the height difference D2 was 2 μm.

[0075] [Experimental Example 2] The gas sensor 10 shown in Figs. 1 to 10 was produced by the above-mentioned production method as Experimental Example 2. The gas sensor 10 of Experimental Example 2 was produced by the same method as Experimental Example 1, except that the sensor element 20 was provided with the first protective layer 91. In producing the sensor element 20 of Experimental Example 2, the pattern of the unfired protective layer that becomes the first protective layer 91 after firing was formed using a slurry prepared by mixing raw material powder (alumina powder), binder solution (polyvinyl acetal and butyl carbitol), solvent (acetone), and a pore former. The thickness T1 of the portion of the first protective layer 91 covering the lead 75b of Experimental Example 2 was 2 µm. The thicknesses T2 and T3 were the same as those of Experimental Example 1, and the height difference D1 (= T1 + D2) between the first protective layer 91 and the upper connector electrode 71b was 4 µm. The porosity P1 of the first protective layer 91 was measured by the above-mentioned method and was 8.9%.

[0076] [Experimental Examples 3-14] Experimental Examples 3 to 14 were produced by fabricating the same gas sensor 10 as in Experimental Example 2, except that the thickness T1, porosity P1, and height difference D1 were variously changed as shown in Table 1. The thicknesses T2 and T3 in Experimental Examples 3 to 14 were the same as in Experimental Examples 1 and 2. Therefore, in all of Experimental Examples 3 to 14, the height difference D1 was equal to the sum of the thickness T1 and the height difference D2 (= 2 μm).

[0077] [Checking wear resistance and conductivity] A heat vibration test was performed on the gas sensors 10 of Experimental Examples 1 to 14 to confirm the wear resistance of the leads 75b and the electrical continuity between the upper connector electrodes 71b and the contact fittings 52b. The heat vibration test was performed twice, and after each test, the leads 75b were observed by photographing their appearance to confirm the wear resistance of the leads 75b. Specifically, if no wear was observed on the leads 75b even after the second heat vibration test, the wear resistance was judged to be "very good (A)". If no wear was observed on the leads 75b after the first heat vibration test but wear was observed after the second heat vibration test, the wear resistance was judged to be "good (B)". If wear was observed on the leads 75b after the first heat vibration test, the wear resistance was judged to be "poor (F)". In the cases where the abrasion resistance was evaluated as "B" or "F", the first protective layer 91 was worn away and the lead 75b was exposed, and it was considered that the lead 75b was worn away due to direct contact between the support portion 53b and the lead 75b. In addition, during the first heating vibration test, the potential of the upper connector electrode 71b was continuously measured to check whether or not a momentary potential abnormality occurred due to vibration. If no momentary potential abnormality occurred, the result of the continuity check was judged to be "good (A)" since no conduction failure occurred between the contact fitting 52b and the upper connector electrode 71b. If a momentary potential abnormality occurred, it was considered that a momentary conduction failure occurred between the contact fitting 52b and the upper connector electrode 71b due to vibration, and the result of the continuity check was judged to be "poor (F)". The heating vibration test was performed under the following conditions with the gas sensor 10 attached to the exhaust pipe of a propane burner installed in a vibration tester.

[0078] Gas temperature: 850℃; Gas air ratio λ:1.05; Vibration conditions: 50Hz→100Hz→150Hz→250Hz sweep for 30 minutes; Acceleration: 30G, 40G, 50G; Test duration: 150 hours.

[0079] The thickness T1, porosity P1, height difference D1, abrasion resistance evaluation results, and electrical continuity confirmation results for each of Experimental Examples 1 to 14 are summarized in Table 1. Note that in Experimental Example 1, since the first protective layer 91 was not present, the values ​​of porosity P1 and height difference D1 are "-" (no value).

[0080] [Table 1]

[0081] As can be seen from Table 1, in Experimental Examples 2 to 9, and 12 to 14, in which the thickness T1 of the portion of the first protective layer 91 covering the lead 75b is 2 μm or more and the porosity P1 of the first protective layer 91 is 20% or less, the abrasion resistance was evaluated as "very good (A)" or "good (B)". In contrast, in Experimental Example 1, in which the thickness T1 is less than 2 μm, and Experimental Examples 10 and 11, in which the porosity P1 exceeds 20%, the abrasion resistance was evaluated as "poor (F)". From these results, it was confirmed that abrasion of the lead 75b can be suppressed if the thickness T1 is 2 μm or more and the porosity P1 is 20% or less.

[0082] Among experimental examples 2 to 9 and 12 to 14, experimental examples 2 to 7 and 12 to 14 in which the porosity P1 was 10% or less were evaluated as "very good (A)" in terms of wear resistance, while experimental examples 8 and 9 in which the porosity P1 was more than 10% and 20% or less were evaluated as "good (B)" in terms of wear resistance. These results confirmed that when the porosity P1 was 10% or less, the effect of the first protective layer 91 in suppressing wear of the leads 75b was enhanced.

[0083] In all of the experimental examples 2 to 13, in which the height difference D1 was 22 μm or less, the continuity check result was "good (A)". In contrast, in the experimental example 14, in which the height difference D1 was more than 22 μm, the continuity check result was "poor (F)". From these results, it was confirmed that if the height difference D1 is 22 μm or less, it is possible to suppress poor continuity between the upper connector electrode 71b and the contact metal fitting 52b. The continuity check result was also "good (A)" in the experimental example 1, which does not include the first protective layer 91. This is thought to be because the first protective layer 91 is not included and the height difference D2 is a small value of 2 μm. However, as described above, the abrasion resistance of the experimental example 1 was evaluated as "poor (F)" because it does not include the first protective layer 91.

[0084] From the above results, it was confirmed that in experimental examples 2 to 9, 12, and 13, in which the thickness T1 is 2 μm or more, the porosity P1 is 20% or less, and the height difference D1 is 22 μm or less, it is possible to suppress wear of the lead 75b while suppressing poor conductivity between the upper connector electrode 71b and the contact fitting 52b. [Industrial Applicability]

[0085] INDUSTRIAL APPLICABILITY The present invention can be used in a sensor element and a gas sensor for detecting the concentration of a specific gas, such as NOx, in a measurement gas, such as an exhaust gas from an automobile. [Explanation of symbols]

[0086] 10 gas sensor, 15 assembly, 20 sensor element, 30 protective cover, 31 inner protective cover, 32 outer protective cover, 33 element chamber, 40 element sealing body, 41 cylindrical body, 42 metal shell, 42a thick portion, 42b bottom surface, 43 inner cylinder, 43a flange portion, 43c, 43d reduced diameter portion, 44a to 44c insulator, 45a, 45b powder compact, 46 metal ring, 47 bolt, 48 outer cylinder, 49 space, 50 connector, 51a first housing, 51b second housing, 52, 52a to 52d contact metal, 53a tip portion, 53b support portion, 53c conductive portion, 53d hook portion, 53e holding portion, 54 clamp, 55 lead wire, 57 rubber plug, 58 piping, 59 Fixing member, 60 element body, 60a to 60f first to sixth surfaces, 61 measured gas inlet, 62 reference gas inlet, 63 detection unit, 64 outer electrode, 65 inner main pump electrode, 66 inner auxiliary pump electrode, 67 measurement electrode, 68 reference electrode, 69 heater, 71, 71a to 71d upper connector electrodes, 72 lower connector electrode, 75b, 75c leads, 80 porous layer, 81 inner porous layer, 83 first inner porous layer, 84 second inner porous layer, 85 outer porous layer, 86 first dense layer, 87 second dense layer, 91 first protective layer, 92 second protective layer, C1, C2 contact portions.

Claims

1. A gas sensor for detecting a specific gas concentration in a measurement gas, comprising: An element body having an oxygen ion conductive solid electrolyte layer; a connector electrode disposed on the outside of the element body; a lead disposed on the outside of the element body and electrically connected to the connector electrode; a protective layer covering the lead, the thickness T1 of the portion covering the lead being 2 μm or more, the porosity P1 being 20% ​​or less, and the height difference D1 between the protective layer and the connector electrode being 22 μm or less; A sensor element having a contact metal fitting having a conductive portion that protrudes toward the connector electrode and is in contact with the connector electrode to be electrically conductive, and a support portion that protrudes toward the lead and is in contact with the protective layer; A gas sensor comprising:

2. The porosity P1 of the protective layer is 10% or less.

2. The gas sensor according to claim 1.

3. The element body has an elongated shape having a longitudinal direction, The conductive portion and the support portion of the contact fitting are arranged along the longitudinal direction, The protective layer has a length L in the longitudinal direction of 2 mm or more.

3. The gas sensor according to claim 1 or 2.

4. A height difference D2 obtained by subtracting the height of the connector electrode from the height of the lead is greater than 0 μm. The gas sensor according to any one of claims 1 to 3.

5. The height difference D1 is 4 μm or more. The gas sensor according to any one of claims 1 to 4.

6. The protective layer is a ceramic containing particles of at least one of alumina and zirconia. The gas sensor according to any one of claims 1 to 5.

7. A sensor element for detecting a specific gas concentration in a measurement gas, comprising: An element body having an oxygen ion conductive solid electrolyte layer; a connector electrode disposed on the outside of the element body; a lead disposed on the outside of the element body and electrically connected to the connector electrode; a protective layer covering the lead, the thickness T1 of the portion covering the lead being 2 μm or more, the porosity P1 being 20% ​​or less, and the height difference D1 between the protective layer and the connector electrode being 22 μm or less; A sensor element comprising:

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