Gas Sensors

Abstract

To provide a gas sensor capable of effectively increasing the sealing effect of an insulator and a sensor element by a sealing material.SOLUTION: A gas sensor 1 includes: a sensor element 2 for detecting gas concentration; an insulator 42 for holding the sensor element 2; a sealing material 5 arranged in a recess 421 of the insulator 42; and a housing for holding the insulator 42. The recess 421 of the insulator 42 is in communication with the insertion hole 420 through which the sensor element 2 is inserted, and the sensor element 2 is placed inside. The opening edge portion 421b connected to the insertion hole 420 on the inner bottom surface 421a of the recess 421 protrudes relative to the surrounding area of the opening edge area 421b.SELECTED DRAWING: Figure 6

Description

[Technical field]

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

[0002] Gas sensors are used to detect the concentration of oxygen gas, other specific gases, and other gases contained in a detection target gas such as exhaust gas. A sensor element is used in the gas sensor, which is provided with a detection electrode exposed to the detection target gas and a reference electrode exposed to the atmosphere. The gas sensor employs a sealing structure that prevents the detection target gas from leaking into the atmosphere through a gap between the sensor element and an insulator that holds the sensor element.

[0003] For example, in the gas sensor of Patent Document 1, it is described that the gap between the inner surface of the insulator and the outer surface of the sensor element is sealed with a glass sealant. It is also described that the contact interface of the glass sealant with the insulator and the contact interface of the glass sealant with the sensor element are in a protruding state from other parts. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2002-82089 A Summary of the Invention [Problem to be solved by the invention]

[0005] The technology described in Patent Document 1 enhances the sealing effect between the insulator and the sensor element by the deformation that occurs in the shape of the glass sealant when the glass sealant melts and solidifies. In other words, in Patent Document 1, no ingenuity is given to the shape of the recess of the insulator in which the glass sealant is housed. Therefore, further ingenuity is required to enhance the sealing effect of the glass sealant.

[0006] The present invention has been made in view of the above problems, and has an object to provide a gas sensor capable of effectively enhancing the sealing effect between the insulator and the sensor element by the sealing material. [Means for solving the problem]

[0007] One aspect of the present invention is a sensor element (2) for detecting a gas concentration; an insulator (42) having an insertion hole (420) through which the sensor element is inserted, and a recess (421) communicating with the insertion hole and continuing from the insertion hole, in which the sensor element is disposed; a sealant (5) disposed in the recess for holding the sensor element to the insulator; a housing (41) having a holding hole (410) for holding the insulator; An opening edge portion (421b) connected to the insertion hole on the inner bottom surface (421a) of the recess is in the gas sensor (1) and protrudes in comparison with the surrounding area of ​​the opening edge portion. Effect of the Invention

[0008] In the gas sensor of the above aspect, an opening edge portion in the inner bottom surface of the recess of the insulator, which is connected to the insertion hole, is protruded in comparison with the surrounding portion of the opening edge portion. With this configuration, when a sealant is placed in the recess of the insulator and the sensor element is held on the insulator, the sealant can be easily brought into contact with the opening edge portion protruding from the inner bottom surface of the recess, and the contact area between the sealant and the insulator can be increased by the sealant contacting the opening edge portion.

[0009] Therefore, according to the gas sensor of the above aspect, the sealing effect between the insulator and the sensor element by the sealing material can be effectively improved.

[0010] In addition, the symbols in parentheses for each component shown in one aspect of the present invention indicate a correspondence with the symbols in the figures in the embodiment, but do not limit each component to only the contents of the embodiment. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram showing a cross section of a gas sensor according to an embodiment. [Diagram 2] FIG. 2 is an explanatory diagram showing a cross section of a sensor element of the gas sensor according to the embodiment. [Diagram 3] FIG. 3 is an explanatory diagram showing a cross section taken along line III-III in FIG. 2 according to the embodiment. [Figure 4] FIG. 4 is an explanatory diagram showing a cross section taken along line IV-IV of FIG. 2 according to the embodiment. [Diagram 5] FIG. 5 is an explanatory diagram showing an intermediate body in which a sensor element, an insulator, and a sealing material are assembled according to the embodiment. [Figure 6] FIG. 6 is an enlarged view of a portion of FIG. 5 according to the embodiment. [Figure 7] FIG. 7 is an explanatory view showing an enlarged view of a part of an intermediate body having a different sealing material configuration according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A preferred embodiment of the above-mentioned gas sensor will now be described with reference to the drawings. <Embodiment> As shown in FIG. 1, the gas sensor 1 of this embodiment includes a sensor element 2, an insulator 42, a sealant 5, and a housing 41. The sensor element 2 is for detecting a gas concentration. The housing 41 has a holding hole 410 for holding the insulator 42. As shown in FIG. 5, the insulator 42 has an insertion hole 420 through which the sensor element 2 is inserted, and a recess 421 that communicates with the insertion hole 420 and is continuous from the insertion hole 420 and in which the sensor element 2 is disposed. The sealant 5 is disposed in the recess 421 and is for holding the sensor element 2 to the insulator 42. As shown in FIG. 6, an opening edge portion 421b connected to the insertion hole 420 in an inner bottom surface 421a of the recess 421 protrudes compared to a surrounding portion of the opening edge portion 421b.

[0013] The gas sensor 1 of this embodiment will be described in detail below. (Gas sensor 1) 1, the gas sensor 1 is disposed at a mounting port 71 of an exhaust pipe 7 of an internal combustion engine of a vehicle, and is used to detect the concentrations of oxygen, specific gases, etc. contained in exhaust gas G flowing through the exhaust pipe 7 as the detection target gas. The gas sensor 1 may be used as an air-fuel ratio sensor (A / F sensor) that determines the air-fuel ratio in the internal combustion engine based on the concentrations of oxygen, unburned gas, etc. in the exhaust gas G.

[0014] A catalyst for purifying harmful substances in the exhaust gas G is disposed in the exhaust pipe 7, and the gas sensor 1 may be disposed either upstream or downstream of the catalyst in the flow direction of the exhaust gas G in the exhaust pipe 7. The gas sensor 1 may also be disposed in a pipe on the intake side of a supercharger that uses the exhaust gas G to increase the density of the air taken in by the internal combustion engine. The pipe in which the gas sensor 1 is disposed may also be a pipe in an exhaust gas recirculation mechanism that recirculates a portion of the exhaust gas G exhausted from the internal combustion engine to the exhaust pipe 7 to the intake pipe of the internal combustion engine.

[0015] (Sensor element 2) 2 to 4, the sensor element 2 of this embodiment is formed in a long rectangular shape, and includes a solid electrolyte body 31, an exhaust electrode 311, an air electrode 312, a first insulator 33A, a second insulator 33B, a gas chamber 35, an air duct 36, and a heating element 34. The sensor element 2 is of a laminated type in which the insulators 33A, 33B, and the heating element 34 are laminated on the solid electrolyte body 31.

[0016] In this embodiment, the longitudinal direction L of the sensor element 2 refers to the direction in which the sensor element 2 extends in an elongated shape. A direction perpendicular to the longitudinal direction L in which the solid electrolyte body 31 and the insulators 33A and 33B are stacked, in other words, a direction in which the solid electrolyte body 31, the insulators 33A and 33B, and the heating element 34 are stacked, is referred to as a stacking direction D. A direction perpendicular to the longitudinal direction L and the stacking direction D is referred to as a width direction W. In addition, in the longitudinal direction L of the sensor element 2, a side exposed to the exhaust gas G is referred to as a tip side L1, and a side opposite to the tip side L1 is referred to as a base side L2.

[0017] (Solid electrolyte body 31, exhaust electrode 311, and air electrode 312) As shown in FIGS. 2 to 4, the solid electrolyte body 31 converts oxygen ions (O 2- ) conductivity. An exhaust electrode 311 exposed to exhaust gas G is provided on a first surface 301 of the solid electrolyte body 31, and an air electrode 312 exposed to air A is provided on a second surface 302 of the solid electrolyte body 31. The exhaust electrode 311 and the air electrode 312 are arranged in a position overlapping with each other in a stacking direction D via the solid electrolyte body 31 at a portion of the tip side L1 exposed to exhaust gas G in the longitudinal direction L of the sensor element 2. At a portion of the tip side L1 in the longitudinal direction L of the sensor element 2, a detection unit 21 is formed by the exhaust electrode 311, the air electrode 312, and a portion of the solid electrolyte body 31 sandwiched between these electrodes 311 and 312. The first insulator 33A is laminated on the first surface 301 of the solid electrolyte body 31, and the second insulator 33B is laminated on the second surface 302 of the solid electrolyte body 31.

[0018] The solid electrolyte body 31 is made of a zirconia-based oxide, and is made of stabilized zirconia or partially stabilized zirconia, which is mainly composed of zirconia (containing 50 mass% or more) and in which a part of the zirconia is replaced by a rare earth metal element or an alkaline earth metal element. A part of the zirconia constituting the solid electrolyte body 31 can be replaced by yttria, scandia, or calcia.

[0019] The exhaust electrode 311 and the air electrode 312 contain platinum as a precious metal that exhibits catalytic activity against oxygen, and a zirconia-based oxide as a common material with the solid electrolyte body 31. The common material is intended to maintain the bonding strength between the exhaust electrode 311 and the air electrode 312, which are formed of the electrode material, and the solid electrolyte body 31, when a paste-like electrode material is printed (applied) on the solid electrolyte body 31 and the solid electrolyte body 31 and the electrode material are fired.

[0020] 2, an electrode lead portion 313 is connected to the exhaust electrode 311 and the atmosphere electrode 312 for electrically connecting these electrodes 311, 312 to the outside of the gas sensor 1. The electrode lead portion 313 is extended to a portion of the base end side L2 in the longitudinal direction L of the sensor element 2.

[0021] (Gas Chamber 35) As shown in Figs. 2 to 4, a gas chamber 35 surrounded by the first insulator 33A and the solid electrolyte body 31 is formed adjacent to the first surface 301 of the solid electrolyte body 31. The gas chamber 35 is formed at a position on the tip side L1 of the first insulator 33A in the longitudinal direction L, where the gas chamber 35 accommodates the exhaust electrode 311. The gas chamber 35 is formed as a space enclosed by the first insulator 33A, the diffusion resistance portion 32, and the solid electrolyte body 31. The exhaust gas G flowing in the exhaust pipe 7 passes through the diffusion resistance portion 32 and is introduced into the gas chamber 35.

[0022] (Diffusion resistor 32) 2, the diffusion resistance portion 32 is provided adjacent to the tip side L1 in the longitudinal direction L of the gas chamber 35. In other words, the diffusion resistance portion 32 is formed on the tip surface 201 in the longitudinal direction L of the element body 20. The diffusion resistance portion 32 is formed by disposing a porous body of a metal oxide such as aluminum oxide in an inlet port opened in the first insulator 33A adjacent to the tip side L1 in the longitudinal direction L of the gas chamber 35. The diffusion speed (flow rate) of the exhaust gas G introduced into the gas chamber 35 is determined by limiting the speed at which the exhaust gas G passes through the pores of the porous body in the diffusion resistance portion 32.

[0023] The diffusion resistance portion 32 may be formed adjacent to both sides of the gas chamber 35 in the width direction W. In this case, the diffusion resistance portion 32 is disposed in an inlet that is opened in the first insulator 33A adjacent to both sides of the gas chamber 35 in the width direction W. Note that the diffusion resistance portion 32 can be formed using a pinhole, which is a small through hole communicating with the gas chamber 35, other than being formed using a porous body.

[0024] (Atmospheric Duct 36) As shown in Figs. 2 and 3, an air duct 36 surrounded by the second insulator 33B and the solid electrolyte body 31 is formed adjacent to the second surface 302 of the solid electrolyte body 31. The air duct 36 is formed from a portion of the second insulator 33B in the longitudinal direction L that houses the air electrode 312 to a base end position in the longitudinal direction L of the sensor element 2 that is exposed to the air A. A base end opening 361 is formed at the base end position in the longitudinal direction L of the sensor element 2 as an air introduction part of the air duct 36. The air duct 36 is formed from the base end opening 361 to a position that overlaps with the gas chamber 35 in the stacking direction D via the solid electrolyte body 31. The air A is introduced into the air duct 36 from the base end opening 361.

[0025] (Insulators 33A and 33B) As shown in Figs. 2 to 4, the first insulator 33A forms the gas chamber 35, and the second insulator 33B forms the air duct 36 and embeds the heating element 34. The first insulator 33A and the second insulator 33B are made of a metal oxide such as alumina (aluminum oxide). Each of the insulators 33A and 33B is formed as a dense body through which the gas, which is the exhaust gas G or the air A, cannot pass, and each of the insulators 33A and 33B has almost no pores through which the gas can pass.

[0026] (Terminal portion 22 of sensor element 2) 1 and 2, the terminal portion 22 of the sensor element 2 is electrically connected to the base ends in the longitudinal direction L of the electrode lead portions 313 of the exhaust electrode 311 and the atmosphere electrode 312, and a pair of heating element lead portions 342 (described later). The terminal portion 22 is disposed on both side surfaces of the base end in the longitudinal direction L of the sensor element 2. The base ends in the longitudinal direction L of the electrode lead portions 313 and the heating element lead portions 342 are connected to the terminal portion 22 via through holes formed in the insulators 33A, 33B.

[0027] (Another configuration of sensor element 2) Although not shown in the drawings, the sensor element 2 is not limited to having one solid electrolyte body 31, but may have two or more solid electrolyte bodies 31. The electrodes 311, 312 provided on the solid electrolyte body 31 are not limited to a pair of the exhaust electrode 311 and the air electrode 312, but may be multiple pairs of electrodes.

[0028] (Heater 34) 2 to 4, the heating element 34 is embedded in the second insulator 33B forming the atmosphere duct 36, and has a heating portion 341 that generates heat when current is applied, and a heating element lead portion 342 connected to a base end side L2 in the longitudinal direction L of the heating portion 341. The heating portion 341 is disposed at a position where at least a portion of it overlaps with the exhaust electrode 311 and the atmosphere electrode 312 in the stacking direction D of the solid electrolyte body 31 and the insulators 33A, 33B. The heating element 34 may be embedded in the first insulator 33A.

[0029] Moreover, the heat generating portion 341 is formed by a linear conductor portion that meanders with straight and curved portions. The straight portions of the heat generating portion 341 in this embodiment are formed parallel to the longitudinal direction L. The heat generating element lead portion 342 is formed by a linear conductor portion that is parallel to the longitudinal direction L. The resistance value per unit length of the heat generating portion 341 is greater than the resistance value per unit length of the heat generating element lead portion 342. The heat generating element lead portion 342 is drawn out from the heat generating portion 341 to a portion on the base end side L2 in the longitudinal direction L. The heat generating element 34 contains a metallic material having electrical conductivity.

[0030] (Protective layer 37) 1, the protective layer 37 is made of a plurality of ceramic particles bonded together as a ceramic material having pores. Pores (gaps) through which the exhaust gas G can pass are formed between the ceramic particles.

[0031] (Housing 41) 1, the housing 41 is used to fasten the gas sensor 1 to a mounting port 71 of the exhaust pipe 7. The housing 41 has a flange portion 411 constituting a maximum outer diameter portion, a tip side tubular portion 412 formed on a tip side L1 in the longitudinal direction L of the flange portion 411, and a base side tubular portion 413 formed on a base side L2 in the longitudinal direction L of the flange portion 411. A male thread that is fastened to the female thread of the mounting port 71 is formed on the outer periphery of the base side L2 in the longitudinal direction L of the tip side tubular portion 412.

[0032] (Insulator 42) As shown in FIG. 1 and FIG. 5, the insulator 42 is disposed in a holding hole 410 that penetrates the center of the housing 41 in the longitudinal direction L. The insulator 42 is also called a first insulator and is made of an insulating ceramic material. An insertion hole 420 that penetrates in the longitudinal direction L is formed in the center of the insulator 42 to insert the sensor element 2. A recess 421 in which a sealant 5 is disposed is formed and communicates with the end of the insertion hole 420 on the base end side L2 in the longitudinal direction L. The sensor element 2 is fixed to the insulator 42 by the sealant 5 disposed in the recess 421 in a state where it is inserted into the insertion hole 420 of the insulator 42.

[0033] As shown in Fig. 6, the recess 421 is formed by an inner bottom surface 421a as an end surface on the inside in the longitudinal direction L, and an annular inner wall surface 421e perpendicular to the inner bottom surface 421a. The cross-sectional area perpendicular to the longitudinal direction L of the recess 421 is larger than the cross-sectional area perpendicular to the longitudinal direction L of the insertion hole 420. In the inner bottom surface 421a of the recess 421, an opening edge portion 421b, which is a portion on the center side near the insertion hole 420, and an outer peripheral side portion 421c near the inner wall surface 421e, protrude from a remaining portion 421d of the inner bottom surface 421a. The protrusion means that the insulator 42 is in a state of being raised from the inner bottom surface 421a toward the opening side (base end side L2) in the longitudinal direction L.

[0034] In this embodiment, the opening edge portion 421b is formed to be 20 μm or more higher than the surrounding portions. In other words, the opening edge portion 421b is formed to protrude from a general portion as the remaining portion 421d of the inner bottom surface 421a toward the opening side (base end side L2) in the longitudinal direction L by 20 μm or more. With this configuration, the sealing effect of the sealant 5 between the insulator 42 and the sensor element 2 can be more effectively improved. The protruding height of the opening edge portion 421b may be, for example, 20 to 200 μm.

[0035] In this embodiment, the opening edge portion 421b is formed as a protruding portion 422 that protrudes in an annular shape. The insertion hole 420 of the insulator 42 is formed as a rectangular hole in accordance with the sensor element 2, whose cross section perpendicular to the longitudinal direction L is formed as a rectangular shape. The protruding portion 422 protrudes in a rectangular ring shape around the insertion hole 420. The cross-sectional area of ​​the insertion hole 420 is larger than the cross-sectional area of ​​the sensor element 2. A gap S is formed between the insertion hole 420 and the sensor element 2.

[0036] The outer periphery side portion 421c is formed as a portion where the inner corner portion between the inner bottom surface 421a and the inner wall surface 421e is tapered. The protruding height of the outer periphery side portion 421c may be, for example, 20 to 200 μm.

[0037] The insulator 42 is formed by compressing a granular ceramic material into a compact and firing the compact. The inner bottom surface 421a and the inner wall surface 421e of the recess 421 of the insulator 42 are formed with unevenness by the granular ceramic material. The surface roughness of the inner bottom surface 421a and the inner wall surface 421e of the recess 421 of the insulator 42 is 10 μm or less in ten-point mean roughness Rz. This configuration makes it easier for the sealant 5 to adhere to the inner bottom surface 421a and the inner wall surface 421e, and makes it easier to ensure airtightness by the sealant 5. The protruding height of the protruding portion 422 as the opening edge portion 421b is greater than the height of the protruding portion of the unevenness on the inner bottom surface 421a.

[0038] 1, a protrusion 423 that forms the maximum outer diameter portion of the insulator 42 is formed on the outer periphery of the insulator 42. When the insulator 42 is placed in the holding hole 410 of the housing 41, a sealant 424 is placed on a tip end side L1 of the protrusion 423 in the longitudinal direction L of the holding hole 410, and crimping materials 425, 426, and 427 are placed on a base end side L2 of the protrusion 423 in the longitudinal direction L of the holding hole 410. The crimping materials 425, 426, and 427 are composed of a powder sealant 425, a cylindrical body 426, and a crimping material 427. The crimping portion 414 of the base end side cylindrical portion 413 of the housing 41 is bent inward in the radial direction R, so that the insulator 42 is crimped and fixed in the holding hole 410 of the housing 41 via the sealing material 424 and crimping materials 425, 426, and 427.

[0039] (Sealant 5) 5 and 6, the sealing material 5 is formed by melting and solidifying various granular ceramic materials, or by compressing various granular ceramic materials. The sealing material 5 may be made of glass obtained by melting and solidifying a glass material. The sealing material 5 may also be made of ceramics obtained by compressing ceramic powder other than glass.

[0040] The sealing material 5 may also contain talc powder as ceramic powder. The entire sealing material 5 may be formed as compressed talc powder. Talc, also known as talc, has excellent heat resistance and is the softest of all inorganic minerals. By compressing the talc powder, the sealing material 5 adheres closely to the insulator 42 and the sensor element 2, and the sealing effect between the insulator 42 and the sensor element 2 can be improved.

[0041] The sealing material 5 may be composed of a glass layer 51 formed by melting and solidifying a glass material, and a ceramic layer 52 formed by compressing ceramic powder other than the glass material, which are laminated in the longitudinal direction L, which is the insertion direction of the sensor element 2. The ceramic layer 52 may be a layer formed by compressing talc powder.

[0042] The sealing material 5 is disposed in the recess 421 of the insulator 42 in which the sensor element 2 is disposed, and is also disposed in the gap S between the sensor element 2 and the insertion hole 420 of the insulator 42. The sensor element 2 is held by the insulator 42 by the sealing material 5.

[0043] 7, the sealing material 5 may be formed in such a manner that the ceramic layers 52 are disposed on both sides in the longitudinal direction L, and the glass layers 51 are disposed between the ceramic layers 52 in the longitudinal direction L. With this configuration, the sealing effect between the insulator 42 and the sensor element 2 can be effectively improved.

[0044] (Auxiliary insulator 43) As shown in FIG. 1, the auxiliary insulator 43 is disposed on the base end side L2 of the insulator 42 in the longitudinal direction L, and holds the contact terminal 44 that contacts the terminal portion 22 of the sensor element 2. The auxiliary insulator 43 is also called a second insulator, and is made of an insulating ceramic material. An insertion hole 430 through which the sensor element 2 is inserted is formed in the center of the auxiliary insulator 43, penetrating the center in the longitudinal direction L. A groove portion 431 for arranging the contact terminal 44 is formed in the auxiliary insulator 43 at a position communicating with the insertion hole 430. The auxiliary insulator 43 is disposed on the inner circumferential side of the base end cover 46A in the radial direction R. The auxiliary insulator 43 is pressed against the insulator 42 by the base end cover 46A via a leaf spring 433.

[0045] (Contact terminal 44) 1, the contact terminal 44 comes into contact with the terminal portion 22 of the sensor element 2 and electrically connects the terminal portion 22 to the lead wire 48. The contact terminal 44 is disposed in the groove portion 431 of the auxiliary insulator 43. The contact terminal 44 is connected to the lead wire 48 via a connecting metal fitting 441, and comes into contact with the terminal portion 22 by applying a restoring force of elastic deformation. A plurality of contact terminals 44 are disposed in accordance with the number of the terminal portions 22 of the sensor element 2, in other words, the number of the electrode lead portions 313 of the exhaust electrode 311 and the atmosphere electrode 312, and the pair of heating element lead portions 342.

[0046] (Tip side cover 45A, 45B) 1, the tip side covers 45A, 45B cover the detection portion 21 of the sensor element 2 protruding from an end face of the tip side L1 in the longitudinal direction L of the housing 41 to the tip side L1. The tip side covers 45A, 45B are attached to the tip side cylindrical portion 412 of the housing 41. The tip side covers 45A, 45B are formed with gas flow holes 451 through which exhaust gas G can flow.

[0047] The detection unit 21 of the sensor element 2 and the tip side covers 45A, 45B are disposed in the exhaust pipe 7 of the internal combustion engine. A part of the exhaust gas G flowing in the exhaust pipe 7 flows into the tip side covers 45A, 45B from the gas communication holes 451 of the tip side covers 45A, 45B. Then, the exhaust gas G in the tip side covers 45A, 45B passes through the protective layer 37 and the diffusion resistance portion 32 of the sensor element 2 and is guided to the exhaust electrode 311.

[0048] (Base end cover 46A, 46B) 1, the base-end covers 46A, 46B cover the wiring portion located on the base-end side L2 in the longitudinal direction L of the gas sensor 1 to protect the wiring portion from water and the like in the atmosphere A. The wiring portion is composed of a contact terminal 44 as a part electrically connected to the sensor element 2, a connection metal fitting 441 between the contact terminal 44 and a lead wire 48, and the like.

[0049] The base end covers 46A, 46B are formed as two separate parts in order to sandwich a water-repellent filter 462 that prevents water in the atmosphere A from entering the gas sensor 1. A bush 47 that holds a plurality of lead wires 48 is held on the inner periphery of a portion of the base end cover 46B on the base end side L2 in the longitudinal direction L. The water-repellent filter 462 is sandwiched between the base end covers 46A, 46B and between the base end cover 46B and the bush 47.

[0050] The base end cover 46B has an air inlet hole 461 for introducing air A from the outside of the gas sensor 1. The water-repellent filter 462 is disposed in a state of covering the air inlet hole 461 from the inner circumferential side of the base end cover 46B. The base end opening 361 of the air duct 36 in the sensor element 2 is open to the space in the base end covers 46A, 46B. The air A that has passed through the water-repellent filter 462 and been taken into the base end covers 46A, 46B flows from the base end opening 361 of the air duct 36 of the sensor element 2 into the air duct 36 and is led to the air electrode 312 in the air duct 36.

[0051] (Bush 47 and lead wire 48) As shown in FIG. 1, the bush 47 is disposed on the inner periphery of the base end cover 46B and holds the plurality of lead wires 48 by sealing them. The bush 47 is made of an elastically deformable rubber material in order to function as a sealing material. The bush 47 has through holes through which the lead wires 48 are inserted. The base end cover 46B is crimped to the bush 47, thereby sealing gaps between the lead wires 48 and the through holes and between the bush 47 and the base end cover 46B. The lead wires 48 are for connecting the contact terminals 44 to a sensor control device 6 outside the gas sensor 1.

[0052] (Sensor control device 6) As shown in Fig. 1, the lead wires 48 of the gas sensor 1 are electrically connected to a sensor control device 6 that controls gas detection in the gas sensor 1. The sensor control device 6 performs electrical control of the gas sensor 1 in cooperation with an engine control device that controls the combustion operation of the engine. As shown in Fig. 2, the sensor control device 6 is provided with a current measurement circuit 61 that measures a current flowing between the exhaust electrode 311 and the atmospheric electrode 312, a voltage application circuit 62 that applies a voltage between the exhaust electrode 311 and the atmospheric electrode 312, an energization circuit that energizes the heating element 34, and the like. The sensor control device 6 may be built in the engine control device.

[0053] (Other gas sensor 1) The gas sensor 1 may detect the concentration of a specific gas component such as NOx (nitrogen oxides). In the NOx sensor, a pump electrode that pumps oxygen to an air electrode 312 by application of a voltage is disposed on the upstream side of the flow of exhaust gas G in contact with the exhaust electrode 311 in the solid electrolyte body 31. The air electrode 312 is also formed at a position overlapping the pump electrode in the stacking direction D via the solid electrolyte body 31.

[0054] (Manufacturing method of gas sensor 1) 5, when manufacturing the gas sensor 1, the sensor element 2 is inserted into the insertion hole 420 of the insulator 42, and glass or ceramic powder constituting the sealant 5 is placed in the recess 421 of the insulator 42 in which the sensor element 2 is placed. At this time, a part of the glass or ceramic powder is also placed in the gap S of the insertion hole 420 through which the sensor element 2 is inserted from the recess 421. Then, the intermediate body in which the sensor element 2, the insulator 42, and the sealant 5 are assembled is heated for heat treatment.

[0055] When a calcined solid glass is used as the sealing material 5, the glass melts when the intermediate body is heated. At this time, in the initial stage of softening of the glass, the softened glass deforms so as to cling to the sensor element 2 due to surface tension. The softened glass also adheres closely to the protruding portion 422 as the opening edge portion 421b of the inner bottom surface 421a. In particular, when the heat treatment temperature is increased to improve the heat resistance, water resistance, etc. of the gas sensor 1, glass with a high melting point may be used. In this case, although there is a risk that the wettability of the glass may decrease, the glass adheres closely to the protruding portion 422, and thus the sealing material 5 can ensure airtightness between the insulator 42 and the sensor element 2.

[0056] Furthermore, when ceramic powder is used for the sealing material 5, the protrusion 422 is formed on the inner bottom surface 421a as the opening edge portion 421b, so that it is possible to increase the pressure applied to the ceramic powder from the protrusion 422 and the sensor element 2 in the vicinity of the protrusion 422. Therefore, it is possible to ensure airtightness between the insulator 42 and the sensor element 2 by the sealing material 5.

[0057] In the gas sensor 1 manufactured as described above, whether glass or ceramic powder is used for the sealing material 5, the sealing effect between the insulator 42 and the sensor element 2 is enhanced. Thus, the exhaust gas G is prevented from leaking into the atmosphere A through the gap between the insulator 42 and the sensor element 2.

[0058] (Action and effect) In the gas sensor 1 of this embodiment, an opening edge portion 421b in an inner bottom surface 421a of a recess 421 of an insulator 42, which is connected to the insertion hole 420, is made to protrude in comparison with a portion surrounding the opening edge portion 421b. With this configuration, when the sealant 5 is disposed in the recess 421 of the insulator 42 and the sensor element 2 is held by the insulator 42, the sealant 5 comes into contact with the opening edge portion 421b protruding from the inner bottom surface 421a of the recess 421, so that the sealant 5 can easily come into contact with the insulator 42. Furthermore, the contact area between the sealant 5 and the insulator 42 can be increased by the sealant 5 coming into contact with the opening edge portion 421b.

[0059] Therefore, according to the gas sensor 1 of this embodiment, the sealing effect of the sealing material 5 between the insulator 42 and the sensor element 2 can be effectively improved.

[0060] The present invention is not limited to the respective embodiments, and further different embodiments can be configured without departing from the scope of the present invention. The present invention also includes various modified examples, modifications within the scope of equivalents, etc. Furthermore, the combinations and forms of various components envisioned from the present invention are also included in the technical spirit of the present invention. [Explanation of symbols]

[0061] 1 Gas sensor 2 Sensor element 41 Housing 410 Retaining hole 42 Insulator 420 Insertion hole 421 Recess 421a Inner bottom surface 421b Opening edge area 5. Encapsulating material

Claims

1. A sensor element (2) for detecting a gas concentration; an insulator (42) having an insertion hole (420) through which the sensor element is inserted, and a recess (421) communicating with the insertion hole and continuing from the insertion hole, in which the sensor element is disposed; a sealant (5) disposed in the recess for holding the sensor element to the insulator; and a housing (41) having a holding hole (410) for holding the insulator. The gas sensor (1), wherein an opening edge portion (421b) connected to the insertion hole in the inner bottom surface (421a) of the recess protrudes compared to a surrounding portion of the opening edge portion.

2. 2. The gas sensor according to claim 1, wherein the opening edge portion is higher than the surrounding portion by 20 [mu]m or more.

3. 3. The gas sensor according to claim 1, wherein the opening edge portion is formed as a protruding portion protruding in an annular shape.

4. 3. The gas sensor according to claim 1, wherein the sealing material contains talc powder.

5. 3. The gas sensor according to claim 1, wherein the sealing material has a glass layer (51) formed by melting and solidifying glass, and a ceramic layer (52) formed by compressing ceramic powder other than the glass, which are laminated in an insertion direction of the sensor element.

6. 3. The gas sensor according to claim 1, wherein the recess of the insulator has a surface roughness of 10 [mu]m or less in ten-point height difference Rz.

Images