Gas sensor and sensor element

Abstract

The present invention provides a gas sensor and a sensor element, which suppress lead wear and conduction failure between a connector electrode and a contact metal member. The gas sensor includes a sensor element (20) and a contact metal member (52b). The sensor element (20) includes: an element main body (60) having a solid electrolyte layer with oxygen ion conductivity; an upper connector electrode (71b) disposed outside the element main body (60); a lead (75b) disposed outside the element main body (60) and electrically connected to the upper connector electrode (71b); and a first protective layer (91) covering the lead (75b), the thickness T1 of the covered portion of the lead (75b) being 2 μm or more, the porosity P1 being 20% or less, and the height difference D1 between the first protective layer and the upper connector electrode (71b) being 22 μm or less. The contact metal member (52b) has a conduction portion (53c) protruding toward the upper connector electrode (71b) and electrically connected to the upper connector electrode 71b in contact therewith, and a support portion (53b) protruding toward the lead (75b) and in contact with the first protective layer (91).

Description

Technical Field

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

[0002] Conventionally, there has been known a gas sensor that detects the concentration of a specific gas such as NOx in a gas to be measured such as exhaust gas of an automobile. For example, the gas sensor of Patent Document 1 includes a sensor element and a contact metal member, and the contact metal member is electrically connected to an electrode provided on the surface of the sensor element. The contact metal member is an elongated member formed by bending a metal, and includes a support portion and a conduction portion that protrude toward the sensor element. When the contact metal member is pressed against the sensor element, the support portion contacts the surface of the sensor element, and the conduction portion contacts the electrode of the sensor element. Accordingly, electrical conduction between the sensor element and the contact member is maintained through the conduction portion, and the support portion also contacts the sensor element, thereby preventing the sensor element from cracking due to the pressing force from the conduction portion.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2014-209104 Summary of the Invention

[0006] However, a lead wire is connected to the electrode of the sensor element. When the lead wire is disposed outside the sensor element, the lead wire sometimes contacts the support portion of the contact metal member and is worn due to friction. In order to suppress such wear, it is considered to coat the lead wire with a protective layer to prevent direct contact between the lead wire and the support portion. However, if the lead wire is coated with a protective layer, the conduction between the conduction portion and the electrode may sometimes become insufficient due to the thickness of the protective layer.

[0007] The present invention has been made to solve the above problems, and a main object thereof is to suppress wear of a lead wire and suppress poor conduction between a connector electrode and a contact metal member.

[0008] The present invention employs the following means to achieve the above main object.

[0009] The gas sensor of the present invention is a gas sensor for detecting the concentration of a specific gas in a gas to be measured, and includes a sensor element and a contact metal member,

[0010] The sensor element includes:

[0011] an element main body having a solid electrolyte layer with oxygen ion conductivity;

[0012] a connector electrode disposed outside the element main body;

[0013] a lead wire disposed outside the element body and electrically connected to the connector electrode; and

[0014] A protective layer, the protective layer covers the lead wire, the thickness T1 of the portion covering the lead wire is greater than 2 μm, the porosity P1 is less than 20%, and the height difference D1 between the protective layer and the connector electrode is less than 22 μm,

[0015] The contact metal member includes a conducting portion that protrudes toward the connector electrode and contacts with the connector electrode to be electrically connected, and a supporting portion that protrudes toward the lead wire and contacts with the protective layer.

[0016] In the gas sensor, the porosity P1 of the protective layer between the lead and the support portion is less than 20% and the thickness T1 of the portion of the protective layer covering the lead is greater than 2μm. Therefore, the protective layer can protect the lead from being damaged by the support portion, thereby suppressing lead wear. In addition, although there is a tendency that the greater the thickness T1, the greater the height difference D1 between the protective layer and the connector electrode, by making the height difference D1 less than 22μm, it is possible to suppress: the height of the protective layer is too large relative to the height of the connector electrode, resulting in insufficient contact between the conductive part and the connector electrode, resulting in poor conduction between the conductive part and the connector electrode. Accordingly, in the gas sensor of the present invention, it is possible to suppress lead wear and poor conduction between the connector electrode and the contact metal part. 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 the value obtained by subtracting the height of the connector electrode from the height of the protective layer.

[0017] In the gas sensor of the present invention, the porosity P1 of the protective layer may be 10% or less, thereby improving the effect of the protective layer in suppressing abrasion of the lead wire.

[0018] In the gas sensor of the present invention, the element body may be in the shape of an elongated strip having a length direction, the conductive portion and the support portion of the contact metal member are arranged along the length direction, and the length L of the protective layer in the length direction is greater than 2 mm. Accordingly, even when the relative positions of the protective layer and the support portion are offset in the length direction, it is easy to maintain the state in which the protective layer exists between the support portion and the lead to protect the lead. Therefore, it is possible to prevent the support portion from directly contacting the lead and causing the lead to be worn.

[0019] 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 wire can exceed 0 μm. When the height difference D2 exceeds 0 μm, that is, when the height of the lead wire is greater than the height of the connector electrode, since there is a protective layer further above the lead wire, the height difference D1 tends to become large. However, even in such a case, by making the height difference D1 22 μm or less, conduction failure between the connector electrode and the contact metal member can be suppressed.

[0020] In the gas sensor of the present invention, the height difference D1 can be 4 μm or more. In the gas sensor of the present invention, the protective layer can be a ceramic containing particles of at least any one of alumina and zirconia.

[0021] The sensor element of the present invention is a sensor element for detecting the concentration of a specific gas in a gas to be measured, and includes:

[0022] An element main body having a solid electrolyte layer with oxygen ion conductivity;

[0023] A connector electrode disposed outside the element main body;

[0024] A lead wire disposed outside the element main body and electrically connected to the connector electrode; and

[0025] A protective layer covering the lead wire, the thickness T1 of the portion covering the lead wire being 2 μm or more, the porosity P1 being 20% or less, and the height difference D1 from the connector electrode being 22 μm or less.

[0026] This sensor element, like the sensor element of the above gas sensor, has a protective layer with a porosity P1 of 20% or less, the thickness T1 of the portion covering the lead wire being 2 μm or more, and the height difference D1 from the connector electrode being 22 μm or less. Therefore, this sensor element is suitable for the sensor element used in the above gas sensor of the present invention. For example, when a contact metal member is mounted on this sensor element, if the conduction portion of the contact metal member is made to conduct with the connector electrode and the support portion of the contact metal member is made to contact the portion of the protective layer covering the lead wire, lead wire wear can be suppressed and conduction failure between the connector electrode and the contact metal member can be suppressed. It should be noted that various modes of the above gas sensor of the present invention can be adopted in this sensor element. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a longitudinal sectional view showing the state where the gas sensor 10 is mounted on the pipe 58.

[0028] Figure 2It is a perspective view of the sensor element 20.

[0029] Figure 3 is Figure 2 the A - A sectional view of.

[0030] Figure 4 It is a top view of the sensor element 20.

[0031] Figure 5 It is a perspective view of the connector 50.

[0032] Figure 6 is Figure 5 the B - B sectional view of.

[0033] Figure 7 It is a perspective view of the contact metal part 52.

[0034] Figure 8 It is an explanatory diagram showing the contact portions C1, C2 between the sensor element 20 and the contact metal part 52.

[0035] Figure 9 is Figure 8 a partial enlarged view of the C - C section of.

[0036] Figure 10 is Figure 8 a partial enlarged view of the D - D section of.

[0037] Symbol Explanation

[0038] 10…Gas sensor, 15…Assembly, 20…Sensor element, 30…Protective cover, 31…Inner protective cover, 32…Outer protective cover, 33…Element chamber, 40…Element seal, 41…Cylindrical body, 42…Main body metal part, 42a…Thick wall part, 42b…Bottom surface, 43…Inner cylinder, 43a…Flange part, 43c, 43d…Reduced diameter part, 44a~44c…Insulator, 45a, 45b…Pressurized powder body, 46…Metal ring, 47…Bolt, 48…Outer cylinder, 49…Space, 50…Connector, 51a…First housing, 51b…Second housing, 52, 52a~52d…Contact metal part, 53a…End part, 53b…Support part, 53c…Conduction part, 53d…Hook part, 53e…Retention part, 54…Clamping part, 55…Lead wire, 57…Rubber plug, 58…Pipe, 59…Fixing part, 60…Element main body, 60a~60f…First surface~Sixth surface, 61…Measured gas inlet, 62…Reference gas inlet, 63…Detection part, 64…Outer electrode, 65…Inner main pump electrode, 66…Inner auxiliary pump electrode, 67…Measurement electrode, 68…Reference electrode, 69…Heater, 71, 71a~71d…Upper connector electrode, 72…Lower connector electrode, 75b, 75c…Lead wire, 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 part. Detailed implementation mode

[0039] Next, the implementation mode of the present invention will be described with reference to the drawings. Figure 1 It is a longitudinal sectional view showing the state where the gas sensor 10 as one implementation mode of the present invention is installed in the pipe 58. Figure 2 It is a perspective view of observing the sensor element 20 from the upper right front. Figure 3 It is Figure 2 A - A sectional view of Figure 4 It is a top view of the sensor element 20. In this implementation mode, as shown in Figure 2 、 Figure 3 The length direction of the element main body 60 of the sensor element 20 is set as the front - rear direction (length direction), the stacking direction (thickness direction) of the element main body 60 is set as the up - down direction, and the direction perpendicular to the front - rear direction and the up - down direction is set as the left - right direction (width direction).

[0040] As shown in Figure 1As shown, the gas sensor 10 includes: an assembly 15, a bolt 47, an outer cylinder 48, a connector 50, a lead wire 55, and a rubber plug 57. The assembly 15 includes: a sensor element 20, a protective cover 30, and an element seal 40. The gas sensor 10 is installed in a pipe 58 such as an exhaust pipe of a vehicle, and is used to measure the concentration of specific gases such as NOx and O2 contained in the exhaust gas as the gas to be measured (specific gas concentration). In the present embodiment, the gas sensor 10 measures the NOx concentration as the specific gas concentration. The front end side of the two ends (front end and rear end) of the sensor element 20 along the length direction is the side exposed to the gas to be measured.

[0041] As Figure 1 shown, the protective cover 30 includes: a bottomed cylindrical inner protective cover 31 that covers the front end side of the sensor element 20; and a bottomed cylindrical outer protective cover 32 that covers the inner protective cover 31. A plurality of holes for allowing the gas to be measured to flow through are respectively formed in the inner protective cover 31 and the outer protective cover 32. An element chamber 33 is formed as a space surrounded by the inner protective cover 31, and the fifth surface 60e (front end surface) of the sensor element 20 is disposed in the element chamber 33.

[0042] The element seal 40 is a component for sealing and fixing the sensor element 20. The element seal 40 includes: a cylindrical body 41 having a main body metal part 42 and an inner cylinder 43; insulators 44a to 44c; pressure powder bodies 45a, 45b; and a metal ring 46. The sensor element 20 is located on the central axis of the element seal 40 and penetrates the element seal 40 in the vertical direction.

[0043] The main body metal part 42 is a cylindrical metal component. The main body metal part 42 forms a thick wall part 42a whose inner diameter at the front side is smaller than that at the rear side. The protective cover 30 is installed on the same side (front side) of the main body metal part 42 as the front end of the sensor element 20. The rear end of the main body metal part 42 is welded to the flange part 43a of the inner cylinder 43. A part of the inner peripheral surface of the thick wall part 42a forms a bottom surface 42b that is a stepped surface. This bottom surface 42b presses the insulator 44a so that the insulator 44a does not fly forward.

[0044] The inner cylinder 43 is a cylindrical metal component and has a flange part 43a at the front end. The inner cylinder 43 and the main body metal part 42 are welded and fixed coaxially. In addition, in the inner cylinder 43, there are formed: a reduced diameter part 43c for pressing the pressure powder body 45b in the central axis direction of the inner cylinder 43, and a reduced diameter part 43d for pressing the insulators 44a to 44c, the pressure powder bodies 45a, 45b Figure 1 downward by means of the metal ring 46.

[0045] Insulators 44a to 44c and pressure powder bodies 45a, 45b are disposed between the inner peripheral surface of the cylindrical body 41 and the sensor element 20. The insulators 44a to 44c function as supports for the pressure powder bodies 45a, 45b. The pressure powder bodies 45a, 45b are obtained by molding ceramic powder such as talc powder. The pressure powder bodies 45a, 45b are filled between the cylindrical body 41 and the sensor element 20 and compressed, whereby the pressure powder bodies 45a, 45b seal 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.

[0046] The bolt 47 is coaxially fixed to the outside of the main body metal member 42. An external thread portion is formed on the outer peripheral surface of the bolt 47. The external thread portion is inserted into the fixing member 59, the fixing member 59 is welded to the pipe 58, and an internal thread portion is provided on the inner peripheral surface of the fixing member 59. Accordingly, the gas sensor 10 can be fixed to the pipe 58 in a state where a part of the sensor element 20 and the protective cover 30 protrude into the pipe 58 on the front end side of the gas sensor 10.

[0047] The outer cylinder 48 is a cylindrical metal member that covers the inner cylinder 43, the rear end side of the sensor element 20, and the connector 50. The rear part of the main body metal member 42 is inserted inside the outer cylinder 48. The front end of the outer cylinder 48 is welded to the main body metal member 42. A plurality of lead wires 55 connected to the connector 50 are led out to the outside from the rear end of the outer cylinder 48. The connector 50 is in contact with and electrically connected to the upper connector electrode 71 and the lower connector electrode 72 disposed on the surface of the rear end side of the sensor element 20. Through the connector 50, the lead wires 55 are electrically connected to the respective electrodes 64 to 68 and the heater 69 inside the sensor element 20. Hereinafter, the details of the connector 50 will be described. The gap between the outer cylinder 48 and the lead wire 55 is sealed by a rubber plug 57. The space 49 inside the outer cylinder 48 is filled with a reference gas. The sixth surface 60f (rear end surface) of the sensor element 20 is disposed in the space 49.

[0048] As Figures 2 to 4 shown, the sensor element 20 includes: an element main 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 main body 60 has: a plurality of ( Figure 3A laminate obtained by laminating six oxygen ion conductive solid electrolyte layers such as zirconia (ZrO2). The element body 60 has a long rectangular parallelepiped shape with its length direction along the front-rear direction, and has first to sixth surfaces 60a to 60f as the outer surfaces of the up, down, left, right, front, and back respectively. The first to fourth surfaces 60a to 60d are the surfaces of the element body 60 along the length direction, corresponding to the side surfaces of the element body 60. The fifth surface 60e is the front end surface of the element body 60, and the sixth surface 60f is the rear end surface of the element body 60. The dimensions of the element body 60 can be, for example, a length of 25 mm or more and 100 mm or less, a width of 2 mm or more and 10 mm or less, and a thickness of 0.5 mm or more and 5 mm or less. In the element body 60, there are formed a measured gas introduction port 61 that is open on the fifth surface 60e for introducing the measured gas into its interior, and a reference gas introduction port 62 that is open on the sixth surface 60f for introducing a reference gas (here, the atmosphere) serving as a detection reference for the specific gas concentration into its interior.

[0049] The detection unit 63 is used to detect the concentration of a specific gas in the measured gas. The detection unit 63 has a plurality of electrodes disposed on the front end side of the element body 60. In this embodiment, the detection unit 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 peripheral surface of the internal space of the element body 60 and have a tunnel-like structure.

[0050] Since the principle by which the detection unit 63 detects the concentration of a specific gas in the gas to be measured is well-known, a detailed description thereof will be omitted. For example, the detection unit 63 detects the concentration of the specific gas as follows. The detection unit 63 sucks out or sucks in oxygen in the gas to be measured around the inner main pump electrode 65 with respect to the outside (element chamber 33) based on the voltage applied between the outer electrode 64 and the inner main pump electrode 65. In addition, the detection unit 63 sucks out or sucks in oxygen in the gas to be measured around the inner auxiliary pump electrode 66 with respect to the outside (element chamber 33) based on the voltage applied between the outer electrode 64 and the inner auxiliary pump electrode 66. Accordingly, the gas to be measured after the oxygen concentration is adjusted to a specified value reaches around the measurement electrode 67. The measurement electrode 67 functions as a NOx reduction catalyst and reduces the specific gas (NOx) in the gas to be measured that has reached. Then, the detection unit 63 generates an electromotive force between the measurement electrode 67 and the reference electrode 68 according to the reduced oxygen concentration, or generates a current flowing between the measurement electrode 67 and the outer electrode 64 based on the electromotive force, and uses the electromotive force or the current as an electrical signal. The electrical signal generated by the detection unit 63 in this way is a signal representing a value corresponding to the concentration of the specific gas in the gas to be measured (a value from which the concentration of the specific gas can be derived), and is equivalent to the detection value detected by the detection unit 63.

[0051] The heater 69 is a resistor disposed inside the element main body 60. The heater 69 generates heat when powered from the outside and heats the element main body 60. The heater 69 heats and keeps warm the solid electrolyte layer forming the element main body 60, so that the temperature at which the solid electrolyte layer is activated (for example, 800 °C) can be adjusted.

[0052] The upper connector electrode 71 and the lower connector electrode 72 are electrodes respectively disposed on the rear end side of either side surface of the element main body 60 and used for electrical conduction with the outside. Both the upper connector electrode 71 and the lower connector electrode 72 are exposed outside the sensor element 20. In the present embodiment, as the upper connector electrode 71, four upper connector electrodes 71a to 71d are arranged side by side in the left-right direction and disposed on the rear end side of the first surface 60a. Similarly, as the lower connector electrode 72, four electrodes are arranged side by side in 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). Regarding the lower connector electrode 72, Figures 1 to 3Only a part of the lower connector electrodes among the four lower connector electrodes is shown. The upper connector electrode 71 and the lower connector electrode 72 are electrically connected to any one of the plurality of electrodes 64 to 68 and the heater 69 of the detection unit 63, respectively. In the present embodiment, the upper connector electrode 71a is connected to the measurement electrode 67, the upper connector electrode 71b is connected to the outer electrode 64, the upper connector electrode 71c is connected to the inner auxiliary pump electrode 66, the upper connector electrode 71d is connected to the inner main pump electrode 65, and the four lower connector electrodes 72 are respectively connected to the heater 69 and the reference electrode 68. The upper connector electrode 71b and the outer electrode 64 are connected through a lead 75b disposed on the first surface 60a (see Figure 3 , Figure 4 ). The upper connector electrode 71c and the inner auxiliary pump electrode 66 are connected through a lead 75c disposed on the first surface 60a and the fourth surface 60d (see Figure 2 , Figure 4 ) and a lead disposed inside the element body 60. The other connector electrodes are connected to the corresponding electrodes or the heater 69 through leads, through holes, etc. disposed inside the element body 60.

[0053] The leads 75b and 75c are conductors containing precious metals such as platinum (Pt) or high melting point metals such as tungsten (W) and molybdenum (Mo). The leads 75b and 75c are preferably cermet conductors containing precious metals or high melting point metals and the oxygen ion conductive solid electrolyte (zirconia in the present embodiment) contained in the element body 60. In the present embodiment, the leads 75b and 75c are made of a cermet conductor containing platinum and zirconia. The porosity of the leads 75b and 75c can be, for example, 5% or more and 40% or less. The line width (thickness) of the leads 75b and 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 and 75c from the solid electrolyte layer of the element body 60 may be provided between the leads 75b and 75c and the first surface 60a of the element body 60.

[0054] The porous layer 80 is a porous body that covers at least the front end side of the side surfaces, i.e., the first surface 60a and the second surface 60b, of the element body 60 provided with the upper and lower connector electrodes 71 and 72. In the present embodiment, the porous layer 80 includes an inner porous layer 81 that covers the first surface 60a and the second surface 60b, and an outer porous layer 85 disposed outside the inner porous layer 81.

[0055] 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 region from the front end of the first surface 60a where the upper connector electrodes 71a to 71d are disposed to the first dense layer 86 (see Figures 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 protects the outer electrode 64 and the lead 75b from, for example, components such as sulfuric acid in the gas to be measured in the element chamber 33, thereby playing a role in suppressing their corrosion and the like. The second inner porous layer 84 covers the entire region from the front end of the second surface 60b where the lower connector electrode 72 is disposed to the second dense layer 87 (see Figure 2 , 3 ). The second inner porous layer 84 is arranged to be vertically symmetric with the first inner porous layer 83.

[0056] The outer porous layer 85 covers the first to fifth surfaces 60a to 60e. On the first surface 60a and the second surface 60b, the outer porous layer 85 covers the inner porous layer 81, thereby covering these surfaces. The outer porous layer 85 is shorter in the front-back direction than the inner porous layer 81. Different from the inner porous layer 81, the outer porous layer 85 only covers the front end and the region near the front end of the element body 60. Accordingly, the outer porous layer 85 covers the peripheral portions of the electrodes 64 to 68 of the detection unit 63 in the element body 60, in other words, covers the portion of the element body 60 that is disposed in the element chamber 33 and exposed to the gas to be measured. Accordingly, the outer porous layer 85 plays a role in suppressing, for example, cracking in the element body 60 caused by the attachment of moisture and the like in the gas to be measured.

[0057] The porosity of the porous layer 80 is 10% or more. The porous layer 80 covers the outer electrode 64 and the gas inlet 61 to be measured. Nevertheless, if the porosity is 10% or more, the gas to be measured can pass through the porous layer 80. The porosity of the inner porous layer 81 can be 10% or more and 50% or less. The porosity of the outer porous layer 85 can be 10% or more and 85% or less. The porosity of the outer porous layer 85 can be higher than the porosity of the inner porous layer 81.

[0058] The first dense layer 86 and the second dense layer 87 suppress the capillary phenomenon of water along the length direction of the element body 60. The first dense layer 86 is disposed on: the first surface 60a where the upper connector electrode 71 and the first inner porous layer 83 are disposed. The first dense layer 86 is disposed such that: it is more rearward than the outer electrode 64 and more forward than the first protective layer 91. The first dense layer 86 is disposed such that: it is more rearward than any one of the plurality of electrodes 64 to 68 included in the detection unit 63 that also includes the outer electrode 64 (see Figure 3 ). The first dense layer 86 is disposed at a position overlapping the insulator 44b in the front-rear direction (see Figure 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 rearward due to capillary phenomenon in the first inner porous layer 83, the first dense layer 86 plays a role of suppressing the passage of moisture through the first dense layer 86, thereby suppressing 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. 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 so as to be separated from the first protective layer 91. As shown in Figure 4 , the first dense layer 86 covers a part of the lead 75b. There is a gap region where the porous layer 80 and the first protective layer 91 do not exist between the first dense layer 86 and the first protective layer 91, and the lead 75b is exposed in the gap region.

[0059] The second dense layer 87 is disposed on: the second surface 60b where the lower connector electrode 72 and the second inner porous layer 84 are disposed. Since the second dense layer 87 is disposed symmetrically with the first dense layer 86 in the up-down direction, the detailed description of the configuration of the second dense layer 87 is omitted. When moisture moves rearward due to capillary phenomenon in the second inner porous layer 84, the second dense layer 87 plays a role of suppressing the passage of moisture through the second dense layer 87, thereby suppressing 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%.

[0060] The length of each of the first dense layer 86 and the second dense layer 87 in the length direction is preferably 0.5 mm or more. By having a length of 0.5 mm or more, the passage of moisture through the first dense layer 86 and the second dense layer 87 can be sufficiently suppressed. The length of the first dense layer 86 and the second dense layer 87 can be 25 mm or less, and can be 20 mm or less. It should be noted that the length of the first dense layer 86 and the length of the second dense layer 87 are the same value in this embodiment, and the two can be different values.

[0061] The first protective layer 91 is a component for protecting the leads 75b and 75c from the contact metal parts 52 of the connector 50. The first protective layer 91 is disposed on: the first surface 60a where the upper connector electrode 71 and the leads 75b and 75c are disposed. The first protective layer 91 covers at least a part of the leads 75b and 75c formed on the first surface 60a. The first protective layer 91 is disposed to be more rearward than the first dense layer 86 and more forward than the upper connector electrode 71. The first protective layer 91 is configured to be more rearward than the insulator 44c (refer to Figure 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 at a position adjacent to the rear end of the upper connector electrode 71 or slightly forward from the upper connector electrode 71. The porosity P1 of the first protective layer 91 is 20% or less. The porosity P1 is preferably 10% or less. The porosity P1 can be lower than the porosity of the porous layer 80.

[0062] The second protective layer 92 is disposed on: the second surface 60b where the lower connector electrode 72 is disposed. The second protective layer 92 is configured to be vertically symmetric with the first protective layer 91. In the present embodiment, since no lead is disposed on the surface of the second surface 60b, the second protective layer 92 does not cover the lead. The second protective layer 92 functions to protect the second surface 60b.

[0063] The connector 50 will be described in detail. Figure 5 is a perspective view of the connector 50. Figure 6 is Figure 5 the B - B cross - sectional view of Figure 7 is a perspective view of the contact metal part 52. Figure 8 is an explanatory view showing the contact portions C1 and C2 between the sensor element 20 and the contact metal part 52. Figure 6 shows a cross - section passing through the upper connector electrode 71b of the sensor element 20. Additionally, Figure 6 the illustration of the lead 75b is omitted in Figure 8 In Figure 4 the periphery of the first protective layer 91 in

[0064] The first housing 51a and the second housing 51b are ceramic components such as alumina sintered bodies. The first housing 51a and the second housing 51b respectively hold a plurality (here, 4) of contact metal parts 52 side - by - side in the direction (left - right direction) orthogonal to the length direction of the sensor element 20.

[0065] The contact metal part 52 is a part made by bending a plate-shaped metal, for example. The contact metal part 52 includes: a terminal part 53a, a support part 53b, a conduction part 53c, a hook part 53d, and a holding part 53e. The terminal part 53a and the hook part 53d are bent in shape, and they are engaged with the first housing 51a and the second housing 51b so that the contact metal part 52 is held by the first housing 51a and the second housing 51b (refer to Figure 6 ). The support part 53b and the conduction part 53c are arranged along the length direction of the contact metal part 52, and the conduction part 53c is arranged at a position closer to the holding part 53e than the support part 53b. Both the support part 53b and the conduction part 53c protrude by bending toward the sensor element 20. The holding part 53e crimps and holds a plurality of core wires of the lead 55 outside the connector 50. It should be noted that Figure 7 shows the state of the holding part 53e before crimping.

[0066] Both the support part 53b and the conduction part 53c of the contact metal part 52 are formed to be elastically deformable, and the spring constant is in the range of, for example, 500 to 4000 N / mm. As shown in Figure 7 , the support part 53b protrudes toward the sensor element 20 with a protruding height H1. The conduction part 53c protrudes toward the sensor element 20 with a protruding height H2. The protruding height H2 of the conduction part 53c is preferably 90% to 110% of the protruding height H1. The closer the protruding height H1 and the protruding height H2 are, the more ideal it is, and it is more preferably that the protruding height H1 and the protruding height H2 are equal. It should be noted that "the protruding height H1 and the protruding height H2 are equal" includes the case where the protruding heights are substantially equal. The protruding heights H1 and H2 are not particularly limited, for example, they are 0.1 mm to 1 mm. For the support part 53b, the radius of curvature R1 of the inner peripheral surface of the end part of the protruding shape ( Figure 7 the upper surface of the support part 53b in Figure 7 ) is, for example, 0.8 to 1.6 mm, and the radii of curvature R2 and R3 of the curved outer peripheral surfaces of both shoulders of the protruding shape ( Figure 7 the upper surface in Figure 7The curvature radii R5 and R6 of the upper surfaces (in ) are, for example, 1.2 mm to 1.5 mm. It should be noted that the curvature radius R2 may be equal to R3, or the curvature radius R5 may be equal to R6. In addition, the curvature radii R5 and R6 may be the same as the curvature radii R2 and R3, or may be greater than the curvature radii R2 and R3. It should be noted that the values of the protrusion height H1, the protrusion height H2, and the curvature radii R1 to R6 described here are all values in the state where the connector 50 is mounted on the sensor element 20 (in the state where the contact metal member 52 is in contact with the sensor element 20).

[0067] The plurality of contact metal members 52 are held by the first housing 51a and the second housing 51b such that the conduction portions 53c thereof are opposed to the upper connector electrode 71 and the lower connector electrode 72 of the sensor element 20 in pairs. Accordingly, the conduction portions 53c of the plurality of contact metal members 52 come into contact with the opposed upper connector electrode 71 and lower connector electrode 72, thereby being electrically connected thereto. In addition, the support portions 53b of the plurality of contact metal members 52 come into contact with the sensor element 20 at positions in front of the upper connector electrode 71 and the lower connector electrode 72 of the sensor element 20. More specifically, they come into contact with the first protective layer 91 and the second protective layer 92 of the sensor element 20. Figure 8 In, the positions of the contact portion C1 between the support portion 53b and the first protective layer 91 and the contact portion C2 between the conduction portion 53c and the upper connector electrode 71 are indicated by a dotted line frame. The positions of the contact portions of the contact metal member 52 with the lower connector electrode 72 and the second protective layer 92 are the same as those of Figure 8 and are thus not shown for simplicity.

[0068] The contact metal members held by the first housing 51a and in contact with the upper connector electrodes 71a to 71d among the plurality of contact metal members 52 are referred to as contact metal members 52a to 52d for distinction (see Figure 5 ). For example, the conduction portion 53c of the contact metal member 52b comes into contact with the upper connector electrode 71b at the contact portion C2 shown in Figure 8 , and the support portion 53b of the contact metal member 52b comes into contact with the first protective layer 91 at the contact portion C1 in front of the upper connector electrode 71b. The conduction portion 53c of the contact metal member 52c comes into contact with the upper connector electrode 71c at the contact portion C2 shown in Figure 8 , and the support portion 53b of the contact metal member 52c comes into contact with the first protective layer 91 at the contact portion C1 in front of the upper connector electrode 71c. As shown in Figure 8 , a lead 75b exists directly below the contact portion C1 between the support portion 53b of the contact metal member 52b and the first protective layer 91. A lead 75c exists directly below the contact portion C1 between the support portion 53b of the contact metal member 52c and the first protective layer 91.

[0069] The clamping member 54 is obtained by bending a plate-shaped metal into a C shape, and has an elastic force capable of pressing in a direction in which the first housing 51a and the second housing 51b are clamped and brought closer to each other. The clamping member 54 holds the first housing 51a and the second housing 51b by using this elastic force. In addition, due to the pressing force from the clamping member 54, the support portion 53b and the conduction portion 53c of the contact metal member 52 are elastically deformed respectively, so that the sensor element 20 is clamped and fixed. Due to the pressing force brought about by the elastic deformation of the support portion 53b and the conduction portion 53c, the connector 50 can clamp and fix the sensor element 20. In addition, since the conduction portion 53c is elastically deformed, the electrical conduction between the conduction portion 53c and the upper connector electrode 71 and the lower connector electrode 72 can be maintained.

[0070] Here, the positional relationship among the upper connector electrode 71b, the lead wire 75b, the first protective layer 91, and the contact metal member 52b will be described in detail. Figure 9 is Figure 8 A partial enlarged view of the C-C cross section of. Figure 10 is Figure 8 A partial enlarged view of the D-D cross section of. It should be noted that, for the convenience of explanation, Figure 10 the height differences D1 and D2 described later are exaggeratedly illustrated in. As Figure 9 , 10 shown, the first protective layer 91 covers the lead wire 75b, and thus exists between the lead wire 75b and the support portion 53b of the contact metal member 52b located directly above the lead wire 75b. Accordingly, the first protective layer 91 protects the lead wire 75b from the support portion 53b. The thickness T1 of the portion of the first protective layer 91 that covers the lead wire 75b is 2 μm or more. The thickness T1 is the thickness of the portion of the first protective layer 91 directly above the lead wire 75b. In addition, 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 existing between the lead wire 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 can protect the lead wire 75b from the support portion 53b, thereby suppressing the wear of the lead wire 75b. In addition, the height difference D1 between the upper connector electrode 71b connected to the lead wire 75b and the first protective layer 91 (refer to Figure 10) is 22 μm or less. Here, when the height difference D1 is too large, that is, when the height of the first protective layer 91 (here, the height of the upper surface of the first protective layer 91) is too large relative 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 conduction portion 53c of the contact metal member 52b and the upper connector electrode 71b may be insufficient. As a result, conduction failure between the conduction portion 53c and the upper connector electrode 71b may easily occur. By making the height difference D1 22 μm or less, such conduction failure can be suppressed. Accordingly, in the gas sensor 10 of the present embodiment, by making the thickness T1 of the first protective layer 91 2 μm or more, the porosity P1 20% or less, and the height difference D1 22 μm or less, wear of the lead 75b can be suppressed and conduction failure between the upper connector electrode 71b and the contact metal member 52b can be suppressed. The larger the thickness T1, the higher the effect of suppressing wear of the lead 75b. However, there is a tendency that the larger the thickness T1, the larger the height difference D1. In the gas sensor 10 of the present embodiment, by making the thickness T1 2 μm or more and the height difference D1 22 μm or less, the above-mentioned wear suppression and conduction failure suppression are achieved concurrently. It should be noted 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 the 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 can exceed 0 μm or can be 4 μm or more.

[0071] In addition, in the present embodiment, the height difference D2 obtained by subtracting the height of the upper connector electrode 71b from the height of the lead 75b (see Figure 10 ) exceeds 0 μm. That is, the height of the lead 75b is greater than the height of the upper connector electrode 71b. In the present embodiment, as Figure 10 shows, the thickness T2 of the lead 75b is greater than the thickness T3 of the upper connector electrode 71b, and thus 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 and is a positive value, the height difference D1 will not be 0 μm and will surely exceed 0 μm (positive value). Even in this case, if the height difference D1 is 22 μm or less, for the above reasons, conduction failure between the conduction portion 53c of the contact metal member 52b and the upper connector electrode 71b can be suppressed. The height difference D2 can be 2 μm or more. When the thickness T2 > the thickness T3, a part of the lead 75b can cover the front end portion of the upper connector electrode 71b. That is, the lead 75b and the upper connector electrode 71b can partially overlap. Accordingly, conduction between the lead 75b and the upper connector electrode 71b can be made more reliable.

[0072] 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 is dense, and wear of the first protective layer 91 itself at the contact portion C1 between the first protective layer 91 and the support portion 53b is suppressed. Accordingly, wear of the first protective layer 91 that causes contact between the support portion 53b and the lead wire 75b can be suppressed, and further wear of the lead wire 75b is thus suppressed.

[0073] The thickness T1 of the first protective layer 91 can be 10 μm or more. The greater the thickness T1, the more improved the effect of the first protective layer 91 in suppressing wear of the lead wire 75b. The thickness T1 can be 20 μm or less.

[0074] The length L of the first protective layer 91 in the length direction of the sensor element 20 (here, the front-rear direction) (refer to Figure 4 , Figure 10 ) is preferably 2 mm or more. If the length L is 2 mm or more, even when the relative position of the first protective layer 91 and the support portion 53b of the contact metal member 52b is displaced in the length direction, it is easy to maintain a state in which the first protective layer 91 exists between the support portion 53b and the lead wire 75b to protect the lead wire 75b. In other words, the position of the contact portion C1 between the sensor element 20 and the contact metal member 52b is not likely to deviate from the first protective layer 91. Therefore, direct contact between the support portion 53b and the lead wire 75b that causes wear of the lead wire 75b can be suppressed. The length L can be 6 mm or less. The distance Lg between the first protective layer 91 and the front end of the upper connector electrode 71 (refer to Figure 4 , Figure 10 ) can be, for example, 0 μm or more. In the present embodiment, the first protective layer 91 is disposed to be separated from the upper connector electrode 71 toward the front, and the distance Lg is a value greater than 0 μm.

[0075] It should be noted that the wear of the lead 75b and the poor conduction between the upper connector electrode 71b and the contact metal member 52b have been described above. However, it can be said that the same applies to 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 and the poor conduction between the upper connector electrode 71c and the contact metal member 52c can be suppressed. In this way, when there are multiple leads covered by the first protective layer 91, if each lead, the connector electrode connected to the lead, and the first protective layer 91 all satisfy the above conditions of the thickness T1, porosity P1, and height difference D1, the wear of the lead can be suppressed and the poor conduction of the connector electrode can be suppressed. When there are multiple leads covered by the first protective layer 91, it is sufficient that at least one of the multiple leads and the connector electrode connected to the lead satisfy the above conditions of the thickness T1, porosity P1, and height difference D1. In addition, regarding the multiple leads covered by the first protective layer 91, it is preferable that the lead and the connector electrode connected to the lead satisfy the above conditions of the thickness T1, porosity P1, and height difference D1. In the present embodiment, the leads 75b and 75c have the same thickness, the upper connector electrodes 71b and 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, in the gas sensor 10 of the present embodiment, the effects of suppressing the wear of the lead 75b and the poor conduction between the upper connector electrode 71b and the contact metal member 52b, and the effects of suppressing the wear of the lead 75c and the poor conduction between the upper connector electrode 71c and the contact metal member 52c can be obtained simultaneously.

[0076] In the present embodiment, the first protective layer 91 does not cover the leads connected to the upper connector electrodes 71a and 71d. However, the height difference between the first protective layer 91 and each of the upper connector electrodes 71a and 71d is also preferably 22 μm or less. Accordingly, the poor conduction between the contact metal member 52 and the upper connector electrodes 71a and 71d can be suppressed. In the present embodiment, since the second protective layer 92 does not cover the leads, it has nothing to do with the effect of suppressing the wear of the leads. However, the height difference between the second protective layer 92 and the lower connector electrode 72 is preferably 22 μm or less. Accordingly, the poor conduction between the contact metal member 52 and the lower connector electrode 72 can be suppressed.

[0077] The first protective layer 91 is preferably a ceramic containing ceramic particles as constituent particles, more preferably containing at least any one of alumina, zirconia, spinel, cordierite, titanium dioxide, and magnesia particles. The first protective layer 91 is further preferably a ceramic containing at least any one of alumina and zirconia particles as constituent particles. In the present embodiment, the first protective layer 91 is 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 may also be made of the same ceramic as the first protective layer 91. In the present embodiment, they are the same alumina ceramic as the first protective layer 91.

[0078] The porosity P1 of the first protective layer 91 is set to a value derived as follows using an image (SEM image) obtained by observing with 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 cross-section is filled with resin and polished to prepare an observation specimen. Next, the magnification of the SEM is set from 1000 times to 10000 times, and the observation surface of the observation specimen is photographed to obtain an SEM image of the first protective layer 91. Next, the obtained image is subjected to image analysis, and based on the brightness distribution of the pixel brightness data in the image, a threshold value is determined by discriminant analysis (Otsu's binarization). Thereafter, based on the determined threshold value, each pixel in the image is binarized into an object part and a pore part, 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 set to values derived in the same manner.

[0079] The thicknesses T1 to T3, the height differences D1, and the height difference D2 are set to values measured as follows using SEM images in the same manner as 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 measurement is performed as follows. First, the cross-section passing through the center of the upper connector electrode 71b in the width direction (here, the left-right direction) of the sensor element in the first protective layer 91 (the cross-section along the length direction of the sensor element) is set as the observation surface for taking the SEM image. Next, based on the pixel brightness data in the obtained SEM image, the existence regions of the first protective layer 91, the lead 75b, and the upper connector electrode 71b in the SEM image are determined respectively. Then, in the SEM image, the thickness of the first protective layer 91 is measured with the three points including the center and both ends along the length direction of the part covering the lead 75b (the part directly above the lead 75b) in the first protective layer 91 as the measurement sites, and the average value of the thicknesses of these three points is set as the thickness T1. Similarly, in the SEM image, the thickness of the lead 75b is measured with the three points including the center and both ends of the part covered by the first protective layer 91 (the part directly below the first protective layer 91) as the measurement sites, and the average value of the thicknesses of these three points is set as the thickness T2. Regarding the upper connector electrode 71b, the average value of the thicknesses of the three points including the center and both ends in the SEM image is also set as the thickness T3. For the height difference D2, it is measured in the form of the distance in the height direction (here, the up-down direction) between the average value of the height positions (here, the position of the upper surface of the lead 75b) of the three measurement sites of the lead 75b at the same three measurement sites as those for measuring the thickness T2 in the SEM image and the average value of the height positions (here, the position of the upper surface of the upper connector electrode 71b) of the three measurement sites of the upper connector electrode 71b at the same three measurement sites as those for measuring the thickness T3. For the height difference D1, the height difference D1 is calculated in the form of the sum of the thickness T1 and the height difference D2.

[0080] Next, a method for manufacturing the gas sensor 10 configured as described above will be described. First, a method for manufacturing the sensor element 20 will be described. When manufacturing the sensor element 20, first, a plurality of (six in this case) unburned ceramic green sheets corresponding to the element main body 60 are prepared. In each green sheet, cuts, through holes, grooves, etc. are provided as needed by stamping or the like, or electrode and wiring patterns are screen-printed. The wiring pattern also includes a pattern of unburned leads that become leads 75b and 75c after firing. In addition, by screen printing, unburned porous layers that become the first inner porous layer 83 and the second inner porous layer 84 after firing, unburned dense layers that become the first dense layer 86 and the second dense layer 87 after firing, unburned protective layers that become the first protective layer 91 and the second protective layer 92 after firing, and unburned connector electrodes that become the upper connector electrode 71 and the lower connector electrode 72 after firing are formed on the surfaces corresponding to the first surface 60a and the second surface 60b among the green sheets. After that, a plurality of green sheets are stacked. The plurality of stacked green sheets are an unburned element main body that becomes the element main body after firing. Then, the unburned element main body is fired to obtain an element main body 60 having leads 75b, lead 75c, upper connector electrode 71, lower connector electrode 72, first protective layer 91, and second protective layer 92, etc. Next, an outer porous layer 85 is formed by plasma spraying to obtain the sensor element 20.

[0081] It should be noted that the porosity P1 of the first protective layer 91 can be adjusted by adjusting, for example, the amount of pore-forming material contained in the unburned protective layer. The viscosity of the unburned protective layer can be adjusted by adjusting, for example, the amount of solvent contained in the unburned protective layer, thereby adjusting the thickness T1 of the first protective layer 91. In addition, the thickness T1 can also be adjusted by the number of screen printing times when forming the unburned protective layer. The adjustment of the thickness T2 of the lead 75b and the thickness T3 of the upper connector electrode 71b is the same. By adjusting the thicknesses T1 to T3 as described above, the height differences D1 and D2 can also be adjusted. The length L of the first protective layer 91 can be adjusted by the shape of the screen printing mask when forming the unburned protective layer.

[0082] Next, a gas sensor 10 embedded with a sensor element 20 is manufactured. First, the sensor element 20 is axially passed through the inside of the cylindrical body 41, and an insulator 44a, a pressure powder body 45a, an insulator 44b, a pressure powder body 45b, an insulator 44c, and a metal ring 46 are arranged in this order between the inner peripheral surface of the cylindrical body 41 and the sensor element 20. Next, the metal ring 46 is pressed to compress the pressure powder bodies 45a and 45b, and in this state, reduced diameter portions 43c and 43d are formed, thereby manufacturing an element sealing body 40 to seal between the inner peripheral surface of the cylindrical body 41 and the sensor element 20. After that, the protective cover 30 is welded to the element sealing body 40, and the mounting bolt 47 is installed to obtain an assembly 15.

[0083] Next, a plurality (here, eight) of lead wires 55 are passed through the rubber plug 57, and then, the core wires of the lead wires 55 are surrounded by the holding portions 53e of the plurality (here, eight) of contact metal members 52 and crimped, thereby electrically connecting the contact metal members 52 and the lead wires 55. Next, with the first housing 51a and the second housing 51b each holding four contact metal members 52, 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 clamped and fixed by a clamping member 54. Accordingly, the plurality of contact metal members 52 are respectively in a state where the support portion 53b contacts and conducts with the first protective layer 91 or the second protective layer 92 and the conduction portion 53c contacts with the upper connector electrode 71 or the lower connector electrode 72. After connecting the connector 50 to the rear end side of the sensor element 20 in this way, the outer cylinder 48 is welded and fixed to the main body metal member 42 to obtain the gas sensor 10.

[0084] Next, a usage example of the gas sensor 10 configured as described above will be described below. When the gas sensor 10 is installed in the pipe 58 as Figure 1 shown, when the gas to be measured flows in the pipe 58, the gas to be measured 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 gas to be measured. Moreover, when the gas to be measured passes through the porous layer 80 and reaches the outer electrode 64 and reaches the inside of the sensor element 20 from the gas to be measured inlet 61, as described above, the detection unit 63 generates an electric signal corresponding to the NOx concentration in the gas to be measured. By taking out this electric signal via the upper connector electrode 71 and the lower connector electrode 72, the NOx concentration is detected based on the electric signal.

[0085] Here, the correspondence between the components of this embodiment and the components of the present invention is clarified. The element main body 60 of this embodiment corresponds to the element main body of the present invention, the upper connector electrode 71b corresponds to the connector electrode, the lead wire 75b corresponds to the lead wire, the first protective layer 91 corresponds to the protective layer, and the contact metal member 52b corresponds to the contact metal member.

[0086] For the gas sensor 10 of the present embodiment described in detail above, when 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, wear of the lead wire 75b can be suppressed and poor conduction between the upper connector electrode 71b and the contact metal piece 52b can be suppressed. It should be noted that if the lead wire 75b is worn, the resistance value of the lead wire 75b may change, causing the electrical signal taken out from the sensor element 20 to change, resulting in a decrease in the detection accuracy of a specific gas concentration. In addition, if the wear of the lead wire 75b intensifies, the lead wire 75b may sometimes break. By suppressing the wear of the lead wire 75b, such a decrease in detection accuracy and wire breakage can be suppressed.

[0087] In addition, when the porosity P1 of the first protective layer 91 is 10% or less, the effect of the first protective layer 91 in suppressing the wear of the lead wire 75b is improved.

[0088] Furthermore, the element main body 60 has a long strip shape with a length direction, the support portion 53b and the conduction portion 53c of the contact metal piece 52b are arranged along the length direction of the element main body 60, and the length L of the first protective layer 91 in this length direction is 2 mm or more. When the length L is 2 mm or more, even when the relative position of the first protective layer 91 and the support portion 53b is displaced in the length direction, it is easy to maintain the state where the first protective layer 91 exists between the support portion 53b and the lead wire 75b to protect the lead wire 75b. Therefore, direct contact between the support portion 53b and the lead wire 75b can be suppressed, and the lead wire 75b can be prevented from being worn. It should be noted that as an example of the relative position of the first protective layer 91 and the support portion 53b being displaced in the length direction, for example, a case of manufacturing error such as the connection position of the connector 50 being displaced when connecting the connector 50 and the sensor element 20 during the manufacture of the gas sensor 10, and a case where the gas sensor 10 vibrates due to the vibration of the vehicle during the use of the gas sensor 10 can be cited.

[0089] Furthermore, the height difference D2 obtained by subtracting the height of the upper connector electrode 71b from the height of the lead wire 75b exceeds 0 μm. When the height difference D2 exceeds 0 μm, that is, when the height of the lead wire 75b is greater than the height of the upper connector electrode 71b, since the first protective layer 91 further exists above the lead wire 75b, the height difference D1 is likely to increase. Even in this case, when the height difference D1 is 22 μm or less, poor conduction between the upper connector electrode 71b and the contact metal piece 52b can be suppressed.

[0090] It should be noted that the present invention is not limited by any of the above embodiments. Of course, as long as it belongs to the technical scope of the present invention, it can be implemented in various ways.

[0091] For example, in the above-described embodiment, the first protective layer 91 covers the lead wires 75b and 75c, but is not limited thereto. The first protective layer 91 only needs to cover at least one lead wire. The first protective layer 91 may cover three or more lead wires.

[0092] In the above-described embodiment, the left and right widths of the first protective layer 91 are the same as the left and right widths of the first surface 60a. However, the first protective layer 91 only needs to cover at least one lead wire, and the left and right widths of the first protective layer 91 may be smaller than the left and right widths of the first surface 60a.

[0093] In the above-described embodiment, the height difference D2 exceeds 0 μm, but is not limited thereto. The height difference D2 may be 0 μm or may be less than 0 μm (negative value). For example, if the thickness T2 of the lead wire 75b is less than the thickness T3 of the upper connector electrode 71b, the height difference D2 may be a negative value. The height difference D2 may be -5 μm or more or may be 0 μm or more. In addition, in the above-described embodiment, the height difference D2 is positive because the thickness T2 > thickness T3, but is not limited thereto. For example, by providing another layer between the lead wire 75b and the element main body 60, it is also possible to make the thickness T2 < thickness T3 and the height difference D2 positive.

[0094] In the above-described embodiment, the height difference D1 exceeds 0 μm, but is not limited thereto. The height difference D1 may be 0 μm or may be less than 0 μm (negative value). For example, if the sum of the thickness T1 of the first protective layer 91 and the thickness T2 of the lead wire 75b is less than the thickness T3 of the upper connector electrode 71b, the height difference D1 can be made less than 0 μm. The height difference D1 may be -22 μm or more, may be -10 μm or more, or may be 0 μm or more.

[0095] In the above-described embodiment, the gas sensor 10 detects the NOx concentration as the concentration of a specific gas, but is not limited thereto, and the concentration of other oxides may be set as the specific gas concentration. When the specific gas is an oxide, similar to the above-described embodiment, oxygen is generated when the specific gas itself is reduced around the measurement electrode 67, and thus the specific gas concentration can be detected based on the detection value of the detection unit 63 corresponding to the oxygen. In addition, the specific gas may be a non-oxide such as ammonia. When the specific gas is a non-oxide, the specific gas is converted into an oxide around, for example, the inner main pump electrode 65 (for example, if it is ammonia, it is oxidized and converted into NO), and oxygen is generated when the converted oxide is reduced around the measurement electrode 67. Therefore, the specific gas concentration can be detected based on the detection value of the detection unit 63 corresponding to the oxygen. In this way, regardless of 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 from the specific gas.

[0096] Example

[0097] Hereinafter, an example of specifically manufacturing a gas sensor will be described as an embodiment. Experimental Examples 2 to 9, 12, and 13 correspond to the embodiments of the present invention, and Experimental Examples 1, 10, 11, and 14 correspond to comparative examples. It should be noted that the present invention is not limited to the following embodiments.

[0098] [Experimental Example 1]

[0099] Except for not having the first protective layer 91, a gas sensor similar to the gas sensor 10 shown in Figures 1 to 10 was manufactured using the above manufacturing method, and it was designated as Experimental Example 1. The sensor element 20 of Experimental Example 1 was manufactured as follows. First, six ceramic green sheets were prepared. The ceramic green sheets were obtained by mixing yttria-stabilized zirconia particles added with 4 mol% stabilizer, an organic binder, and an organic solvent and molding them by tape casting. For each green sheet, patterns such as each electrode were formed by screen printing. The formed patterns included: patterns of unburned leads that would become leads 75b and 75c after firing, and patterns of unburned connector electrodes that would become upper connector electrodes 71 after firing. The pattern of the unburned lead was formed using a slurry obtained by kneading platinum particles, zirconia particles, and a solvent. The pattern of the unburned connector electrode was formed using a slurry obtained by kneading platinum particles, zirconia particles, and a solvent. Then, the six green sheets were stacked and fired. Accordingly, a sensor element 20 having leads 75b and 75c and an upper connector electrode 71 was manufactured. Next, an assembly 15 in which the sensor element 20 was embedded was manufactured, and the connector 50 was connected to the sensor element 20 so that the conduction portions 53c of the eight contact metal members 52 were respectively conducted with the upper connector electrode 71 or the lower connector electrode 72. Then, the outer cylinder 48 was welded and fixed to the main body metal member 42 to manufacture the gas sensor 10 of Experimental Example 1. Since the sensor element 20 of Experimental Example 1 does not have the first protective layer 91, the support portion 53b of the contact metal member 52b is in direct contact with the lead 75b, and the support portion 53b of the contact metal member 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 is 12 μm, the thickness T3 of the upper connector electrode 71b is 10 μm, and the height difference D2 is 2 μm.

[0100] [Experimental Example 2]

[0101] A gas sensor similar to the gas sensor 10 shown in Figures 1 to 10The gas sensor 10 shown is set as Experimental Example 2. The sensor element 20 is provided with a first protective layer 91, and the gas sensor 10 of Experimental Example 2 is fabricated in the same manner as Experimental Example 1 except for this. When fabricating the sensor element 20 of Experimental Example 2, the pattern of the unburned protective layer that becomes the first protective layer 91 after firing is formed using a slurry prepared by mixing raw material powder (aluminum oxide powder), binder solution (polyvinyl butyral and butyl carbitol), solvent (acetone), and pore-forming material. The thickness T1 of the portion of the first protective layer 91 in Experimental Example 2 that covers the lead wire 75b is 2 μm. The thicknesses T2 and T3 are the same as those in Experimental Example 1, and the height difference D1 (=T1 + D2) between the first protective layer 91 and the upper connector electrode 71b is 4 μm. The porosity P1 of the first protective layer 91 is measured by the above method, and the result is 8.9%.

[0102] [Experimental Examples 3 to 14]

[0103] As shown in Table 1, various changes are made to the thickness T1, porosity P1, and height difference D1, and except for this, the gas sensor 10 identical to Experimental Example 2 is fabricated and set as Experimental Examples 3 to 14. The thicknesses T2 and T3 in Experimental Examples 3 to 14 are the same as those in Experimental Examples 1 and 2. Therefore, in Experimental Examples 3 to 14, the height difference D1 is equal to the sum of the thickness T1 and the height difference D2 (=2 μm).

[0104] [Confirmation of Abrasion Resistance and Conductivity]

[0105] The gas sensors 10 of Experimental Examples 1 to 14 were subjected to a heating vibration test to confirm the abrasion resistance of the lead wire 75b and the conduction between the upper connector electrode 71b and the contact metal piece 52b. The heating vibration test was carried out twice. Each time it was carried out, the lead wire 75b was observed through the appearance photo after the implementation, and the abrasion resistance was confirmed by whether the abrasion of the lead wire 75b was seen. Specifically, when no abrasion of the lead wire 75b was seen even after the second heating vibration test was carried out, the abrasion resistance was judged as "very good (A)". When no abrasion of the lead wire 75b was seen after the first heating vibration test was carried out, but abrasion was seen after the second heating vibration test was carried out, the abrasion resistance was judged as "good (B)". When abrasion of the lead wire 75b was seen after the first heating vibration test was carried out, the abrasion resistance was judged as "poor (F)". It should be noted that when the evaluation of the abrasion resistance is "B" or "F", it is considered that: since the first protective layer 91 is worn and the lead wire 75b is exposed, the support portion 53b and the lead wire 75b are in direct contact, resulting in abrasion of the lead wire 75b. In addition, in the first heating vibration test, the potential of the upper connector electrode 71b was continuously measured to confirm whether an instantaneous potential abnormality occurred due to vibration. When no instantaneous potential abnormality occurred, no conduction failure occurred between the contact metal piece 52b and the upper connector electrode 71b. Therefore, the result of the conduction confirmation was judged as "good (A)". When an instantaneous potential abnormality occurred, it was regarded that an instantaneous conduction failure occurred between the contact metal piece 52b and the upper connector electrode 71b due to vibration, and thus the result of the conduction confirmation was judged as "poor (F)". For the heating vibration test, the gas sensor 10 was installed in the exhaust pipe of the propane burner provided in the vibration testing machine, and the heating vibration test was carried out under the following conditions.

[0106] Gas temperature: 850 °C;

[0107] Gas-air ratio λ: 1.05;

[0108] Vibration conditions: Scanning from 50 Hz → 100 Hz → 150 Hz → 250 Hz for 30 minutes;

[0109] Acceleration: 30G, 40G, 50G;

[0110] Test time: 150 hours.

[0111] The respective thicknesses T1, porosities P1, height differences D1, determination results of abrasion resistance, and conduction confirmation results of Experimental Examples 1 to 14 are summarized in Table 1. It should be noted that in Experimental Example 1, since there is no first protective layer 91, the values of the porosity P1 and the height difference D1 are set to "-" (no value).

[0112] Table 1

[0113]

[0114] As can be seen from Table 1, for Test Examples 2 to 9 and 12 to 14 where the thickness T1 of the portion of the first protective layer 91 covering the lead wire 75b is 2 μm or more and the porosity P1 of the first protective layer 91 is 20% or less, the evaluation of abrasion resistance is "very good (A)" or "good (B)". In contrast, for Test Example 1 where the thickness T1 is less than 2 μm, and Test Examples 10 and 11 where the porosity P1 exceeds 20%, the evaluation of abrasion resistance is "poor (F)". From these results, it is confirmed that if the thickness T1 is 2 μm or more and the porosity P1 is 20% or less, abrasion of the lead wire 75b can be suppressed.

[0115] In Test Examples 2 to 9 and 12 to 14, for Test Examples 2 to 7 and 12 to 14 where the porosity P1 is 10% or less, the evaluation of abrasion resistance is "very good (A)", and for Test Examples 8 and 9 where the porosity P1 exceeds 10% and is 20% or less, the evaluation of abrasion resistance is "good (B)". From these results, it is confirmed that if the porosity P1 is 10% or less, the effect of the first protective layer 91 in suppressing abrasion of the lead wire 75b is improved.

[0116] For Test Examples 2 to 13 where the height difference D1 is 22 μm or less, the conduction confirmation results are all "good (A)". In contrast, for Test Example 14 where the height difference D1 exceeds 22 μm, the conduction confirmation result is "poor (F)". From these results, it is confirmed that if the height difference D1 is 22 μm or less, poor conduction between the upper connector electrode 71b and the contact metal member 52b can be suppressed. It should be noted that in Test Example 1 without the first protective layer 91, the conduction confirmation result is also "good (A)". It is considered that this is because there is no first protective layer 91 and the height difference D2 is a small value of 2 μm. However, as described above, in Test Example 1, since there is no first protective layer 91, the evaluation of abrasion resistance is "poor (F)".

[0117] From the above results, it is confirmed that in Test Examples 2 to 9, 12, and 13 where 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, abrasion of the lead wire 75b can be suppressed and poor conduction between the upper connector electrode 71b and the contact metal member 52b can be suppressed.

[0118] Industrial Applicability

[0119] The present invention can be used for sensor elements and gas sensors for detecting the concentration of specific gases such as NOx in measured gases such as automotive exhaust gas.

Claims

1. A gas sensor for detecting the concentration of a specific gas in a gas to be measured, characterized in that the gas sensor includes a sensor element and a contact metal part, the sensor element includes: an element main body having a solid electrolyte layer with oxygen ion conductivity; a connector electrode disposed outside the element main body; a lead wire disposed outside the element main body and electrically connected to the connector electrode; and a protective layer that covers the lead wire, the thickness T1 of the portion covering the lead wire is 2 μm or more, the porosity P1 of the protective layer is 20% or less, and the height difference D1 from the connector electrode is 22 μm or less, the contact metal part has a conduction part that protrudes toward the connector electrode and is in electrical contact with the connector electrode, and a support part that protrudes toward the lead wire and is in contact with the protective layer, the height difference D2 obtained by subtracting the height of the connector electrode from the height of the lead wire exceeds 0 μm.

2. The gas sensor according to claim 1, characterized in that the porosity P1 of the protective layer is 10% or less.

3. The gas sensor according to claim 1 or 2, characterized in that the element main body has a long strip shape with a length direction, the conduction part and the support part of the contact metal part are arranged along the length direction, the length L in the length direction of the protective layer is 2 mm or more.

4. The gas sensor according to claim 1 or 2, characterized in that the height difference D1 is 4 μm or more.

5. The gas sensor according to claim 1 or 2, characterized in that the protective layer is a ceramic containing particles of at least one of alumina and zirconia.

6. A sensor element for detecting the concentration of a specific gas in a gas to be measured, characterized in that the sensor element includes: an element main body having a solid electrolyte layer with oxygen ion conductivity; a connector electrode disposed outside the element main body; a lead wire disposed outside the element main body and electrically connected to the connector electrode; and a protective layer that covers the lead wire, the thickness T1 of the portion covering the lead wire is 2 μm or more, the porosity P1 of the protective layer is 20% or less, and the height difference D1 from the connector electrode is 22 μm or less, the height difference D2 obtained by subtracting the height of the connector electrode from the height of the lead wire exceeds 0 μm.

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