Gas sensor and method for its manufacture

Abstract

Gas sensor (1) comprising: a sensor element (10) having a plate shape extending in one direction along an axial line (O) and having an electrode contact point (11a) on an outer surface of a rear end section thereof; a metallic connection element (20, 30, 40, 50) extending in the direction of the axial line (O) and electrically connected to the electrode contact point (11a); a tubular separator (90, 95) holding the metallic connection element (20, 30, 40, 50) and surrounding the rear end section of the sensor element (10); and a conductor wire (146) which is connected to a rear end section of the metallic connection element (20, 30, 40, 50) and extends behind the separator (90, 95), wherein the metallic connection element (20, 30, 40, 50) has a front locking section (29, 35f, 59) and a rear locking section (45e, 58e) which are attached to the front and rear respectively.are provided at the rear end of the metallic connecting element; wherein the separator (90, 95) consists of a front separator (90) and a rear separator (95) which are located at the front and rear end of the metallic connecting element respectively.rear side in the direction of the axial line (O) are arranged and connected to each other, wherein the front separator (90) has a first locking section with a rearward-facing surface (90s1, 90s2), wherein the rear separator (95) has a second locking section with a forward-facing surface (95s); and wherein the metallic connecting element (20, 30, 40, 50) is held between the front separator (90) and the rear separator (95) such that the front locking section (29, 35f, 59) abuts the rearward-facing surface (90s1, 90s2), and the front locking section (29, 35f, 59) is thereby in locking engagement with the rearward-facing surface (90s1, 90s2) and the rear locking section (45e, 58e) is in locking engagement with the forward-facing surface (95s).

Description

Technical FieldThe present invention relates to a gas sensor having a sensor element for detecting the concentration of a particular gas to be detected, and a method of manufacturing the same.BackgroundA known gas sensor for detecting the concentration of oxygen or NOx in the exhaust gas of an automobile or the like has a plate-like sensor element using solid electrolyte. For example, DE 10 2017 210 236 A1 discloses a gas sensor having a sensor element with an electrode pad and a metal terminal connected thereto, which has a front part, a rear part and a middle part, which are connected to one another and to a lead wire connecting part by a first and a second neck part.In a widely used gas sensor of such a type, a plurality of electrode pads are provided on the outer surface of a rear end portion of the plate-like sensor element, and metal terminal members are brought into electrical contact with the electrode pads to output a sensor output signal from the sensor element and supply electric power to a heater stacked on the sensor element (Patent Document 1).As shown in FIG. 14, each metal terminal member 200 is formed of a metal plate by, for example, cutting and drawing, and has a strip-shaped shape. The metal terminal member 200 includes a folded-back portion 202 whose distal end portion is folded back to a sensor element (not shown) for elastic contact with an electrode pad of the sensor element, and a crimping portion 204 to which a distal end of a lead wire 146 is fixed by crimping.The metal terminal member 200 also has a locking portion 206 protruding in a direction opposite to its folded-back portion 202 and having an L-shaped cross section. The locking portion 206 is accommodated in an L-shaped groove 300 gformed on the front side of a separation hole 300 hof a separator 300. The locking portion 206 comes into locking engagement with a front surface 300 sof the groove 300 g, thereby holding the terminal metal member 200 in the separator 300.Specifically, in the example of FIG. 14, the metal terminal member 200 is rotated counterclockwise by about 90°, with the locking portion 206 being inserted into the upper right groove 300 g. In total, four such metal terminal elements 200 are individually accommodated in different grooves 300 g.The lead wire 146 is connected (crimped) to the metal terminal member 200 as follows. First, the lead wire 146 is inserted into the separation hole 300 hof the separator 300 from the rear side of the separator 300 and pulled out toward the front F side of the separator 300. Next, a distal end portion of the lead wire 146 is fixed by crimping to the crimping portion 204 of the terminal metal member 200 disposed on the front side of the separator 300, thereby connecting the lead wire 146 to the terminal metal member 200.Then, when the lead wire 146 is pulled toward the R rear side so that the lead wire 146 is pulled out behind the separator 300, the metal terminal member 200 connected to the lead wire 146 is also pulled toward the R rear side. As a result, the locking portion 206 is accommodated in the groove 300 gand is in locking engagement with the forward surface 300 sof the groove 300 g, thereby preventing rearward coming-out of the metal terminal member 200. In this way, the metal terminal member 200 is assembled into the separator 300.Prior Art DocumentPatent Document 1Patent Document 1: JP 2012-230 076 A (FIGS. 3 and 4 )SUMMARY OF THE INVENTIONProblem to be Solved by the InventionHowever, in the case of the conventional metal terminal 200, the locking portion 206 prevents only rearward jumping of the metal terminal 200. Therefore, when an external force or the like acts on the metal terminal 200, the metal terminal 200 may move forward, and the electrical connection between the metal terminal 200 and the corresponding electrode pad may become unstable. Also, in the case where the spring-off resistance is increased by decreasing the distance between the locking portion 206 and the wall surface of the groove 300 g, when the metal terminal member 200 is assembled into the separator 300, a larger frictional force is generated between the locking portion 206 and the wall surface of the groove 300 g. In such a case, the lead wire 146 receives a larger drawing load toward the rear R side, thereby decreasing the efficiency of the mounting work.Thus, it is an object of the present invention to provide a gas sensor that can reliably hold metal terminal elements within a separator and can realize a stable electrical connection between the metal terminal elements and the electrode pads of a sensor element. Another object of the present invention is to provide a method for manufacturing such a gas sensor.Means for Solving the ProblemIn order to solve the above problem, a gas sensor of the present invention includes a sensor element; a tubular separator that holds the metal terminal element and surrounds the rear end portion of the sensor element; and a lead wire according to claim 1.According to this gas sensor, the front locking portion of the metal terminal member to which the lead wire is connected is brought into locking engagement with and held by the rear facing surface of the front separator and the front facing surface of the rear separator, respectively. Therefore, it is possible to prevent the metal terminal from dropping toward the front side and the rear side inside the front separator and the rear separator, respectively.As a result, the metallic terminal member is reliably held within the front separator and the rear separator, and the metallic terminal member is prevented from moving in the axial direction due to, for example, the application of an external force or the like, whereby a stable electrical connection can be established between the electrode pad of the sensor element and the above-mentioned metallic terminal member.In addition, since the terminal metal member is held inside the front separator and the rear separator, it is not necessary to excessively reduce the clearances between the terminal metal member and the wall surfaces of the insertion holes of these separators. Therefore, it is possible to prevent an increase in the rear drawing load acting on the lead wire, which would otherwise increase due to an increase in the frictional force generated between the metal terminal member and the wall surfaces of the insertion holes. Thus, a decrease in efficiency of assembly work can be prevented.In the gas sensor of the present invention, a contact point at which the metal terminal member comes into contact with the electrode pad may be disposed between the rearward surface and the forward surface.According to this gas sensor, the metal terminal member is in interlocking engagement with the front separator and the rear separator at two positions located on the front side and the back side of the contact pad. Therefore, it is possible to reliably prevent the metal terminal member that is in contact with the electrode pad at the contact location from moving in the axial direction due to, for example, the application of an external force or the like. Thus, the electrical connection between the metal terminal and the electrode pad becomes more stable.The gas sensor of the present invention may be such that the metal terminal is composed of a front metal terminal and a rear metal terminal disposed at the front and rear sides, respectively, and connected to each other, the front metal terminal having the front locking portion, the rear metal terminal having the rear locking portion; the rear metal terminal being connected to the lead wire and being at least partially accommodated in the rear separator; and the front metal terminal being in contact with the electrode pad and being at least partially accommodated in the front separator.According to this gas sensor, the front metal terminal member having an elastic portion for connection to the electrode pad and thus being complex in shape can be separated from the rear metal terminal member connected to the lead wire and requiring complex work such as a crimping step. Therefore, in the crimping step, it is only necessary to handle the rear metal terminal with a simple shape. Thus, productivity is improved.The gas sensor of the present invention may be such that a front end portion of the rear metal terminal member takes the form of at least a part of a circular column or a cylindrical tube, the front metal terminal member having, at its rear end, a connecting portion taking the form of at least a part of a cylindrical tube, and the front end portion being installed in the connecting portion.According to this gas sensor, the connecting portion and the front end portion are arranged rotationally symmetrically about the axis. Therefore, although the rear metal terminal and the front metal terminal are positionally deviated to some extent about the axis, the front end portion can be fitted into the connecting portion, whereby the rear metal terminal and the front metal terminal can be easily and reliably connected to each other.A gas sensor manufacturing method of the present invention is a method for manufacturing a gas sensor, including: a sensor element having a plate shape extending in an axial line direction and having an electrode pad on an outer surface of a rear end portion thereof; a metallic terminal member extending in the axial line direction and electrically connected to the electrode pad; a tubular separator holding the metallic terminal member and surrounding the rear end portion of the sensor element; and a lead wire connected to a rear end portion of the metallic terminal member and extending to behind the separator, the metallic terminal member having a front locking portion and a rear locking portion provided on the front and rear end sides of the metallic terminal member, respectively, the separator being made up of a front separator and a rear separator, A front separator having a first locking portion with a rearward surface, the rear separator having a second locking portion with a forward surface, the method comprising a step of disposing the front separator and the rear separator on the front side and the rear surface of the metal terminal member, respectively, and holding the metal terminal member between the front separator and the rear separator such that the front locking portion is lockingly engaged with the rearward surface and the rear locking portion is lockingly engaged with the forward surface.This method of manufacturing a gas sensor can also prevent the metal terminal member from dropping toward the front side and the rear side inside the front separator and the rear separator. As a result, the metallic terminal member is reliably held within the front separator and the rear separator, and the metallic terminal member is prevented from moving in the axial direction due to, for example, the application of an external force or the like, whereby a stable electrical connection can be established between the electrode pad of the sensor element and the above-mentioned metallic terminal member. In addition, since the terminal metal member is held inside the front separator and the rear separator, it is not necessary to excessively reduce the clearances between the terminal metal member and the wall surfaces of the insertion holes of these separators. Therefore, it is possible to prevent an increase in the rear drawing load acting on the lead wire, which would otherwise increase due to an increase in the frictional force generated between the metal terminal member and the wall surfaces of the insertion holes. Thus, a decrease in efficiency of assembly work can be prevented.Effect of the inventionThe present invention provides a gas sensor that can reliably hold metal terminal elements within a separator and realizes a stable electrical connection between the metal terminal elements and the electrode pads of a sensor element.Brief Description of the DrawingsFIG. 1 is a sectional view of a gas sensor according to an embodiment of the present invention taken along an axial direction. FIG. 2 shows a perspective view of a front metal connection element. FIG. 3 is a perspective view of another front metal terminal element. FIG. 4 shows a perspective view of a rear metal connection element. FIG. 5 is a perspective view of a front separator. FIGS. 6( a) and 6( b) are views showing a step of mounting the front terminal metal members in the front separator. FIG. 7 is a sectional view showing a state in which the front terminal metal members are held in the front separator. FIGS. 8( a) and 8( b) are views showing a step of mounting the rear terminal metal members in a rear separator. FIGS. 9( a) and 9( b) are sectional views of the front separator having insertion holes thereof. FIGS. 10( a) and 10( b) are sectional views of the rear separator having insertion holes thereof. FIGS. 11( a) and 11( b) are views showing a step of combining the front separator and the rear separator, the views being sectional views along a predetermined cross section shown in FIGS. 9( a) and 9( b), and FIGS. 10( a) and 10( b). FIGS. 12( a) and 12( b) are views showing the step of combining the front separator and the rear separator, the views being sectional views along another cross section shown in FIGS. 9( a) and 9( b), and FIGS. 10( a) and 10( b). FIG. 13 is a perspective view showing a modification of the metal terminal member. FIG. 14 is a perspective view of a conventional metal terminal.Embodiments of the InventionAn embodiment of the present invention will be described next.FIG. 1 is an overall sectional view of a gas sensor 1 (NOx sensor) according to an embodiment of the present invention taken along the direction of an axial line O; FIGS. 2 and 3 are perspective views of front terminal metal members 20 and 30, respectively; FIG. 4 is a perspective view of a rear terminal metal member 40; FIG. 5 is a perspective view of a front separator 90; FIGS. 6 ( a) and 6 ( b) are views showing a step of attaching the front terminal metal members 20 and 30 to the front separator 90; FIG. 7 is a sectional view showing a state in which the front terminal metal members 20 and 30 are held in the front separator 90; FIGS. 8( a) and 8( b) are views showing a step of mounting the rear metal terminal members 40 in a rear separator 95. Note that FIG. 7 is a cross section taken along a line A-A of FIG. 6( b) that extends perpendicular to the direction of the axial line O.The gas sensor 1 is a NOx sensor for detecting the oxygen concentration in the exhaust gas of automobiles as well as various internal combustion engines.The gas sensor 1 shown in FIG. 1 includes: a tubular metallic shell 138 having a threaded portion 139 formed on its outer surface and configured to be fixed to an exhaust pipe; a plate-shaped sensor element 10 extending in the direction of the axial line O (the longitudinal direction of the gas sensor 1 or the vertical direction in the drawing); a tubular ceramic sleeve 106 disposed to radially surround the sensor element 10; a tubular front separator 90 made of ceramic and disposed to surround a rear end portion of the sensor element 10 inserted into a front internal space thereof; six front metal terminal members 20 and 30 (only four of them are illustrated in FIG. 1 ) inserted and held in insertion holes 90 h( 90 h 1 and 90 h 2) extending through the front separator 90 in the direction of the axial line O; a tubular rear separator 95 made of ceramic; and six rear metal terminal members 40 (only two of them are illustrated in FIG. 1 ) held in the rear separator 95.As will be described later, the rear separator 95 is disposed on the rear side and engages with the front separator 90.The front metal terminal members 20 and 30 and the rear metal terminal members 40 are disposed on the front side and the rear side, respectively, and are connected to each other. A member formed by connecting the front metal terminal member 20 (30) and the corresponding rear metal terminal member 40 corresponds to the "metal terminal member" appearing in the claims.As will be described later in detail, as shown in FIG. 5, the insertion holes 90 h 1 and 90 h 2 of the front separator 90 communicate with the front F-side internal space 90 vof the front separator 90, and the front metal terminal members 20 and 30 held in the insertion holes 90 h 1 and 90 h 2 are opposed to the outer surface of a rear end portion of the sensor element 10 and are electrically connected to the respective electrode pads 11 aformed on the outer surface.Three electrode pads 11 aare arranged side by side in the width direction of the sensor element 10 on each of the opposite sides of the rear end portion of the sensor element 10. The electrode pads 11 amay be formed of, for example, a sintered body mainly containing Pt.Meanwhile, a front end side gas sensing portion 11 of the sensor element 10 is covered with a porous protective layer 14 made of alumina or the like.The metallic shell 138 is a generally tubular member formed of stainless steel and has a through hole 154 extending therethrough in the direction of the axial line and a ledge portion 152 projecting radially inward from the through hole 154. The sensor element 10 is disposed in the through hole 154 such that a front end portion thereof protrudes from the front end of the through hole 154. Further, the rail portion 152 is inclined inwardly and inclined from a plane perpendicular to the direction of the axial line.Within the through hole 154 of the metallic shell 138, a generally annular ceramic holder 151 made of alumina, a powder filling layer 153 (hereinafter referred to as talc ring 153), and the above-mentioned ceramic sleeve 106 are stacked in this order from the front side to the back side to radially surround the sensor element 10.In addition, a crimp packing 157 is disposed between the ceramic sleeve 106 and a rear end portion 140 of the metallic shell 138. The rear end portion 140 of the metallic shell 138 is crimped so that the ceramic sleeve 106 is pushed forward by the crimp packing 157.Meanwhile, as shown in FIG. 1, a double protector made of metal (e.g., stainless steel) is fixed to the outer periphery of a front end portion (a lower portion in FIG. 1 ) of the metallic shell 138 by welding or the like and covers a protruding part of the sensor element 10.A sleeve 144 is fixed to the outer periphery of a rear end portion of the metallic shell 138. The lead wires 146 are connected to the rear end portions of the rear metal terminal members 40 and extend rearward from the rear end of the rear separator 95.A grommet 170 made of rubber is disposed in an opening portion provided at a rear end of the sleeve 144 (an upper end in FIG. 1 ), and has lead wire insertion holes 170 hinto which six lead wires 146 (only two of which are illustrated in FIG. 1 ) extending from the rear separator 95 are respectively inserted.The front separator 90 is disposed around a rear end portion (an upper end portion in FIG. 1 ) of the sensor element 10 protruding from the rear end portion 140 of the metallic shell 138, and has a collar portion 90 pprotruding radially outward from the outer surface thereof. The collar portion 90 pcontacts the sleeve 144 through a holding member 169, thereby holding the front separator 90 inside the sleeve 144.The rear separator 95 is disposed between the grommet 170 and the front separator 90, and the elastic force of the grommet 170 causes the rear separator 95 to press the front separator 90 forward. As a result, the collar portion 90 pis pressed against the holding member 169, and the front terminal member 90 and the rear separator 95 are held in the sleeve 144 in a mutually joined state (i.e., without separation in the axial line O direction).FIGS. 2 and 3 are perspective views of the front metal terminal members 20 and 30, respectively.As shown in FIG. 7, since the four front metal terminal members 30 are formed such that the front metal terminal members 30 adjacent to each other in the front separator 90 are axis-symmetric, one of the front metal terminal members 30 (one in the upper left position I in FIG. 7 ) is used for description.The front metal terminal 30 located at the lower left position II in FIG. 7 is asymmetric with the front metal terminal 30 located at the position I with respect to a line along a plane of the sensor element 10. The front metal terminal 30 located at the lower right position III in FIG. 7 is asymmetric with the front metal terminal 30 located at the position II with respect to a line perpendicular to the plane of the sensor element 10. The front metal terminal 30 located at the upper right position IV in FIG. 7 is asymmetric with the front metal terminal 30 located at the position I with respect to the line perpendicular to the plane of the sensor element 10.The two front metal terminal members 20 are disposed in the front separator 90 opposite to each other and have an asymmetric shape; therefore, one of the front metal terminal members 20 (one located at an upper position in FIG. 7 ) is used in the description.The lower front metal terminal 20 in FIG. 7 is axially symmetric with respect to the upper front metal terminal 20 with respect to the line along the plane of the sensor element 10. Each of the front metal terminal members 20 is disposed between the two front metal terminal members 30 with respect to the width direction of the sensor element 10.As shown in FIG. 2, the front metal terminal member 20 extends in the direction of the axial line O and integrally includes: a connection portion 23 to be connected to the rear metal terminal member 40, a substantially plate-like body portion 21 connected to the front end of the connection portion 23, and an elastic portion 22 bent toward the sensor element 10 at the front end of the body portion 21.The front metal terminal 20 can be manufactured, for example, as follows: a blank is punched out from a single metal plate (INCONEL (registered trademark) or the like), and then the blank is bent into a predetermined shape. The manufacturing method is not limited thereto.The connecting portion 23 has a cylindrical tubular shape having a C-shaped portion, and the rear metal terminal member 40 whose front end portion has a cylindrical tubular shape having a C-shaped portion is inserted into the connecting portion 23. In this case, the front metal terminal 20 is indirectly connected to the lead wire 146 via the rear metal terminal 40.A part of the body portion 21 at the center thereof with respect to the direction of the axial line O has wing portions on opposite sides with respect to the width direction thereof. The wing portions are bent 90° toward the sensor element 10 side to thereby form a pair of holding portions 27 whose portions partially form a square U-shaped cross section. The connecting portion 23 is integrally connected to the rear end of the body portion 21. The body portion 21 serves as a base portion of the front metal terminal member 20 to secure the strength of the front metal terminal member 20. The two holding portions 27 fan out towards the rear.Also, a rear end portion of the body portion 21 disposed on the rear side with respect to the orientation of the axial line O includes a pair of quadrangular rear holding portions 25 flush with the body portion 21 and extending outward from opposite sides of the rear end portion of the body portion 21 with respect to the width direction thereof. Similarly, a front end portion of the body portion 21 disposed on the front side with respect to the orientation of the axial line O includes a pair of quadrangular front holding portions 29 flush with the body portion 21 and extending outward from opposite sides of the front end portion of the body portion 21 with respect to the width direction thereof.The pair of quadrangular front holding portions 29 correspond to the "front locking portion" appearing in the claims.The elastic portion 22 is bent rearward from the front end of the body portion 21 and toward the sensor element 10, and is elastically connected to the electrode pad 11 a(see FIG. 1 ) at a contact P 1. The elastic portion 22 elastically bends radially with respect to the body portion 21.As shown in FIG. 3, the front metal terminal member 30 extends in the direction of the axial line O and integrally includes a connection portion 33 to be connected to the rear metal terminal member 40, a generally plate-like body portion 31 connected to the front end of the connection portion 33, and an elastic portion 32 bent toward the sensor element 10 at the front end of the body portion 31.The front metal terminal 30 may be manufactured, for example, as follows: a blank is punched out from a single metal plate (INCONEL (registered trademark) or the like), and then the blank is bent into a predetermined shape. The manufacturing method is not limited thereto. Similar to the connecting portion 23, the connecting portion 33 has a cylindrical tubular shape, and the rear terminal metal member 40 is inserted into the connecting portion 33.The body portion 31 has an L-shaped cross section and has a wing portion on one side with respect to the width direction of the body portion 31. The wing portion is bent 90° toward the sensor element 10 side to thereby form a position holding portion 35. The connecting portion 33 is integrally connected to the rear end of the body portion 31. The body portion 31 serves as a base portion of the front metal terminal member 30 to secure the strength of the front metal terminal member 30. Also, a portion of the position holding portion 35 located slightly forward of the center thereof with respect to the direction of the axial line O is recessed toward the body portion 31 to thereby form a stepped shape, and its front facing surface forms a front end portion 35 f.The front end portion 35 fcorresponds to the "front locking portion" appearing in the claims.The elastic portion 32 is bent rearward from the front end of the body portion 31 and toward the sensor element 10, and is elastically connected to the electrode pad 11 a(see FIG. 1 ) at a contact P 2. The elastic portion 32 elastically bends radially with respect to the body portion 31.Meanwhile, as shown in FIG. 4, the rear metal terminal member 40 extends in the direction of the axial line O and integrally includes a crimp terminal portion 47, a substantially plate-like neck portion 41, a large-diameter cylindrical tubular portion 45, and a cylindrical tubular front end portion 43. The neck portion 41 is connected to the front end of the crimp terminal portion 47. The large diameter portion 45 is connected to the front end of the neck portion 41 and is formed by bending a plate-like portion to have a C-shaped portion. The front end portion 43 is connected to the front end of the large diameter portion 45 and is formed by bending a plate-like portion to have a C-shaped portion.The rear metal terminal 40 may be manufactured, for example, as follows: a blank is punched out from a single metal plate (SUS304 or the like), and then the blank is bent into a predetermined shape. The manufacturing method is not limited thereto.The crimp terminal portion 47 squeezes the exposed conductors 146 wof a front end portion of the lead wire 146, thereby gripping the conductors 146 win a tubular shape.The front end portion 43 has a cylindrical tubular shape and tapers forward. The front end portion 43 is fitted into the tubular connecting portion 23 or 33, whereby the rear metal terminal 40 is electrically connected to the front metal terminal 20 or 30.The large diameter portion 45 has a larger diameter than the crimp terminal portion 47 and the front end portion 43, and a rearward surface 45 eof the large diameter portion 45 is disposed radially outside the crimp terminal portion 47.The rearward facing surface 45 ecorresponds to the "rear locking portion" appearing in the claims.As shown in FIG. 5, the front separator 90 has the insertion holes 90 h 1 and 90 h 2, and the insertion holes 90 h 1 and 90 h 2 communicate with the front F-side internal space 90 vof the front separator 90.The insertion holes 90 h 2 are disposed at four corners of the front separator 90, and the insertion holes 90 h 1 are disposed between two insertion holes 90 h 2 along the width direction of the sensor element 10.A rear facing surface 90 s 1 is formed on the front side of the insertion holes 90 h 1, and a rear facing surface 90 s 2 is formed on the front side of the insertion holes 90 h 2.Each of the rearward facing surfaces 90 s 1 and 90 s 2 corresponds to the "first locking portion" appearing in the claims.Note that recesses 90 rextending along the width direction of the sensor element are formed on the rear facing surface of the rear separator 90 so as to be disposed on opposite sides of the internal space 90 v. As will be described in detail later, the bottoms of the recesses 90 rengage with the protrusions 95 pof the rear separator 95.As shown in FIGS. 6( a) and 6( b), the front holding portions 29 of the front metal terminal member 20 abut against the rearward facing surface 90 s 1 when the front metal terminal member 20 is inserted from the rear side into the insertion hole 90 h 1 (FIG. 6( a) ), thereby preventing the front metal terminal member 20 from coming off toward the front side. Thus, the front metal terminal member 20 is held in the front separator 90 (FIG. 6( b)).Similarly, when the front metal terminal 30 is inserted from the rear side into the insertion hole 90 h 2 (FIG. 6( a) ), the front end portion 35 fof the front metal terminal 30 abuts against the rear facing surface 90 s 2, thereby preventing the front metal terminal 30 from coming off toward the front side. Thus, the front metal terminal 30 is held in the front separator 90 (FIG. 6( b)).In a state where the front terminal metal members 20 and 30 are held in the front separator 90, the connecting portions 23 and 33 protrude rearward from the front separator 90 (FIG. 6( b)).Meanwhile, as shown in FIGS. 8( a) and 8( b), the rear separator 95 has six circumferentially disposed insertion holes 95 h. Each of the insertion holes 95h has a large diameter on the front F side, the diameter gradually decreases near the center with respect to the direction of the axial line O, and the resultant stepped portion forms a front facing surface 95s (Fig. 8(a)).The front facing surface 95 scorresponds to the "second locking portion" appearing in the claims.In the periphery of the front end surface of the rear separator 95, two protrusions 95 pprotruding toward the axial line O are formed. The protrusions 95 pengage with the bottoms of the recesses 90 rof the front separator 90.The lead wire 146 is previously passed through the insertion hole 95 hsuch that a distal end of the lead wire 146 appears on the front side of the rear separator 95, the distal end of the lead wire 146 being connected to the rear metal terminal member 40 on the front side of the rear separator 95. Next, a portion of the rear metal terminal member 40 on the lead wire 146 side is inserted into the insertion hole 95 hfrom the front F side, and the lead wire 146 is pulled rearward. As a result, the rearward surface 45 e(see FIG. 4 ) of the large diameter portion 45 of the rear metal terminal member 40 comes into contact with the forward surface 95 s, thereby preventing the rear metal terminal member 40 from being pulled out toward the rear side. Thus, the rear metal terminal member 40 is held in the rear separator 95 (FIG. 8( b)).In this state, a front portion of the front end portion 43 (a portion of the front end portion 43 located forward of the center with respect to the axial line O direction) of the rear metal terminal member 40 protrudes from the front end surface of the rear separator 95.The outer diameter of the large diameter portion 45 is slightly smaller than the inner diameter of the insertion hole 95h. The large diameter portion 45 engages with the wall surface of the insertion hole 95 h, thereby holding the rear terminal metal member 40 inside the rear separator 95.Next, with reference to FIGS. 9( a) and 9( b), FIGS. 10( a) and 10( b), FIGS. 11( a) and 11( b), and FIGS. 12( a) and 12( b), a method of holding the front terminal metal members 20 and 30 and the rear terminal metal members 40 by the front separator 90 and the rear separator 95 such that the front terminal metal members 20 and 30 and the rear terminal metal members 40 are sandwiched between the front separator 90 and the rear separator 95 in the axial line O direction will be described.Since the front terminal metal members 20 and 30 and the corresponding rear terminal metal members 40 are inserted into different insertion holes of the separators 90 and 95, the cross sections of the separators 90 and 95 including their insertion holes are shown in FIGS. 9( a) and 9( b), and FIGS. 10( a) and 10( b).As shown in FIGS. 9( a) and 9( b), a cross section of the front separator 90 perpendicular to the plate surface of the sensor element 10 passes through the opposing insertion holes 90 h 1 and extends along the direction of the axial line O, which is represented by a line X 1-X 1. Also, a cross section of the front separator 90 perpendicular to the plate surface of the sensor element 10 passes through the opposing insertion holes 90 h 2 and extends along the direction of the axial line O, which is represented by a line X 2-X 2.Similarly to FIGS. 10( a) and 10( b), a cross section of the rear separator 95 extending along the line X 1-X 1 is represented by a line Y 1-Y 1, and a cross section of the rear separator 95 extending along the line X 2-X 2 is represented by a line Y 2-Y 2.FIGS. 11( a) and 11( b) are views showing a step of combining the front separator 90 and the rear separator 95 in which the front separator 90 is shown in cross section along the line X 1-X 1 in FIGS. 9( a) and 9( b) and the rear separator 95 is shown in cross section along the line Y 1-Y 1 in FIGS. 10( a) and 10( b).As shown in FIGS. 11( a) and 11( b), the front holding portion 29 (front locking portion) of the front metal terminal member 20 is in locking engagement with the rearward facing surface 90 s 1 (first locking portion). In addition, the rearward facing surface 45 e(front locking portion) of the corresponding rear metal terminal member 40 is engaged with the forward facing surface 95 s(second locking portion) (FIG. 11( a)).In this state, the protrusions 95 pof the rear separator 95 are brought into engagement with the bottoms of the recesses 90 rof the front separator 90 in the direction of the axial line O with the front separator 90 and the rear separator 95 sandwiched and held between the holding member 169 and the grommet 170, as shown in FIGS. 11( a) and 11( b), with the front separator 90 and the rear separator 95 connected to each other (FIG. 11( b)).At this time, the front end portion 43 of the rear terminal metal member 40 protruding toward the front side of the rear separator 95 is inserted into the connection portion 23 of the front terminal metal member 20 protruding on the rear side of the front separator 90, and the two terminal metal members are connected to each other.In the state where the two metal terminal members are connected to each other, the front holding portion 29 is brought into locking engagement with the rearward facing surface 90 s 1, thereby preventing the front metal terminal member 20 from being pulled out toward the front side. Similarly, the rearward facing surface 45 eis brought into locking engagement with the forward facing surface 95 s, thereby preventing the rearward metal terminal member 40 from being peeled off toward the rear side. Since the front metal terminal member 20 and the rear metal terminal member 40 are joined in the direction of the axial line O to thereby form an integral "metal terminal member", it is possible to prevent the front metal terminal member 20 and the rear metal terminal member 40 from protruding toward the front and the rear inside the front separator 90 and the rear separator 95, respectively.FIGS. 12( a) and 12( b) are views showing the step of combining the front separator 90 and the rear separator 95 in which the front separator 90 is in cross section along the line X 2-X 2 in FIGS. 9( a) and 9( b) and the rear separator 95 is in cross section along the line Y 2-Y 2 in FIGS. 10( a) and 10( b).As shown in FIGS. 12( a) and 12( b), the front end portion 35 f(front locking portion) of the front metal terminal member 30 is in locking engagement with the rearward facing surface 90 s 2 (first locking portion). Also, the rearward facing surface 45 e(front locking portion) of the corresponding rear metal terminal member 40 is in locking engagement with the forward facing surface 95 s(second locking portion) (FIG. 12( a)).In this state, the protrusions 95 pof the rear separator 95 are engaged with the bottoms of the recesses 90 rof the front separator 90 in the direction of the axial line O, and the front separator 90 and the rear separator 95 are sandwiched and held between the holding member 169 and the grommet 170 shown in FIGS. 12( a) and 12( b), with the front separator 90 and the rear separator 95 being joined to each other (FIG. 12( b)).At this time, the front end portion 43 of the rear terminal metal member 40 protruding toward the front side of the rear separator 95 is connected to the connection portion 33 of the front terminal metal member 30 protruding toward the rear side of the front separator 90, and the two terminal metal members are connected to each other.In the state where the two metal terminal members are joined together, the front end portion 35 fis brought into locking engagement with the rearward facing surface 90 s 2, thereby preventing the front metal terminal member 30 from being pulled out toward the front side. Similarly, the rearward facing surface 45 eis brought into locking engagement with the forward facing surface 95 s, thereby preventing the rearward metal terminal 40 from being peeled off toward the rear side. Since the front metal terminal member 30 and the rear metal terminal member 40 are joined in the direction of the axial line O to thereby form an integral "metal terminal member", it is possible to prevent the front metal terminal member 30 and the rear metal terminal member 40 from protruding toward the front and the rear inside the front separator 90 and the rear separator 95, respectively.Note that, in FIGS. 11( a), 11( b), 12( a), and 12( b), one of two metal terminal members (the front metal terminal members 20( 30) or the rear metal terminal members 40) disposed on opposite sides inside the separator (the front separator 90 and the rear separator 95) is omitted to facilitate understanding.As a result of the above-described assemblies, the terminal metal members (the front terminal metal members 20 and 30 and the rear terminal metal members 40) can be reliably held in the separator (the front separator 90 and the rear separator 95). Therefore, the metal terminal members 20 and 30 are prevented from moving in the direction of the axial line O due to, for example, application of an external force or the like, whereby the above-described metal terminal members can be electrically connected to the electrode pads 11 aof the sensor element 10 in a stable state.In addition, it is not necessary to hold the terminal metal members (the front terminal metal members 20 and 30 and the rear terminal metal members 40) by excessively reducing the clearances between the terminal metal members and the wall surfaces of the insertion holes 90 h 1, 90 h 2, and 95 hof the separator (the front separator 90 and the rear separator 95). Therefore, it is possible to prevent an increase in the rear drawing load acting on the lead wire 146, which would otherwise increase due to an increase in the frictional force generated between the metal terminal members and the wall surfaces of the insertion holes 90 h 1, 90 h 2, and 95 h. Thus, a decrease in efficiency of assembly work can be prevented.Note that, in the present embodiment, as shown in FIGS. 11( a) and 11( b), the contact point P 1 between the front metal terminal 20 and the electrode pad 11 ais located between the rearward surface 90 s 1 (the first locking portion) and the forward surface 95 s(the second locking portion) along the direction of the axial line O. Similarly to FIGS. 12( a) and 12( b), the contact point P 2 disposed between the front metal terminal 30 and the electrode pad 11 ais located between the rearward facing surface 90 s 2 (the first locking portion) and the forward facing surface 95 s(the second locking portion) along the direction of the axial line O.As a result, the terminal metal members (the front terminal metal members 20 and 30 and the rear terminal metal members 40) are brought into interlocking engagement with the separator (the front separator 90 and the rear separator 95) at two positions located on the front and rear sides of the pads P 1 and P 2. Therefore, for example, it is possible to more reliably prevent the metal terminal members 20 and 30 that are in contact with the electrode pads 11 aat the contact points P 1 and P 2 from moving toward the axial line O due to the application of external force or the like, for example. Thus, the electrical connection between the metal terminal members 20 and 30 and the electrode pads 11a becomes more stable.In the present embodiment, as described above, two metal terminal members (i.e., the front metal terminal member 20 connected to the electrode pad 11 aof the sensor element 10 and the rear metal terminal member 40 connected to the lead wire 146) are connected as metal terminal members.As a result, the front metal terminal 20 ( 30) having an elastic portion for connecting to the electrode pad 11 aand thus having a complex shape can be separated from the rear metal terminal 40 connected to the lead wire 146 and requiring a complex operation such as a crimping step. Therefore, in the crimping step, it is only necessary to handle the rear metal terminal 40 with a simple shape. Thus, productivity is improved.Also in the present embodiment, as shown in FIGS. 2, 3 to 4, the front end portion 43 of the rear metal terminal member 40 has a cylindrical tubular shape, and rear portions of the front metal terminal members 20 and 30 form the cylindrical tubular connection portions 23 and 33.As mentioned above, since the connecting portions 23 and 33 and the front end portion 43 are rotationally symmetrical about the axial line O, even if the rear metal terminal member 40 and the front metal terminal member 20 or 30 are positioned about the axial line O to some extent, the front end portion 43 can be fitted into the connecting portion 23 or 33, whereby the rear metal terminal member 40 and the front metal terminal member 20 or 30 can be easily and reliably connected to each other.The present invention is not limited to the above embodiment, but extends to various modifications and equivalents encompassed by the ideas and scope of the invention.For example, as shown in FIG. 13, a metal terminal member 50 may be formed as an integral member without dividing the metal terminal member 50 into front and rear portions. In this case, a front portion of the metal terminal member 50 has the same shape as the above-mentioned metal terminal member 20, with the connecting portion 23 removed therefrom and having a body portion 51, an elastic portion 52, rear holding portions 55, holding portions 57, and front holding portions 59 identical in shape to the body portion 21, the elastic portion 22, the rear holding portions 25, the holding portions 27, and the front holding portions 29.Similarly, a rear portion of the terminal metal member 50 has the same shape as the above-mentioned terminal metal member 40, with the front end portion 43 removed therefrom and having a crimp terminal portion 53 and a large diameter portion 58 identical in shape to the crimp terminal portion 47 and the large diameter portion 45, respectively. A portion of the terminal metal member 50 on the front side of the large diameter portion 58 is integrally connected to the body portion 51.In this metal terminal 50, the front holding portion 59 corresponds to the "front locking portion", and the rearward facing surface 58 eof the large-diameter portion 58 corresponds to the "rear locking portion".The terminal metal member and the separator are not limited in shape, etc. to those of the above embodiment.The connection structure (coupling structure) between the rear metal terminal and the front metal terminal is not limited to the above, but may be, for example, as follows: a rear end portion of the front metal terminal may be in the form of a male pin, and the male pin may be inserted into a tubular front end portion of the rear metal terminal.In the case where a rear end portion of the front metal fitting member and a front end portion of the rear metal fitting member take a tubular shape, the tubular shape is not limited to a cylindrical tube, but may be a prismatic tube such as a square tube. The tubular shape may not be a fully closed tube, but may be at least a part of a tube (for example, may have a C-shaped cross section). The pipe of the front metal fitting or the rear metal fitting may be replaced with a circular column or a part of the circular column.Examples of the gas sensor include an oxygen sensor and a full range gas sensor besides a NOx sensor.Description of the Reference Numerals1 Gas sensor 10 Sensor element 11 aElectrode pad 20, 30, 40, 50Metal terminal 20, 30Front metal terminal 23, 33 Connecting portion 29, 35 f, 59Front locking portion 40Metal terminal 43Front end portion of rear metal terminal 45 e, 58 eBack locking portion 90 Separator (front separator) 90 s 1, 90 s 2First locking portion (back surface) 95 Separator (back separator) 95 sSecond locking portion (front surface) 146 Lead wire O axial line P 1, P 2Contact point

Claims

A gas sensor (1) comprising: a sensor element (10) having a plate shape that extends in an axial line (O) direction and that has an electrode pad (11a) on an outer surface of a rear end portion thereof; a metallic terminal element (20, 30, 40, 50) that extends in the axial line (O) direction and is electrically connected to the electrode pad (11a); a tubular separator (90, 95) that holds the metallic terminal element (20, 30, 40, 50) and surrounds the rear end portion of the sensor element (10); and a lead wire (146) connected to a rear end portion of the metal terminal member (20, 30, 40, 50) and extending to behind the separator (90, 95), the metal terminal member (20, 30, 40, 50) having a front locking portion (29, 35f, 59) and a rear locking portion (45e, 58e) provided on the front and rear end sides of the metal terminal member, respectively; wherein the separator (90, 95) is composed of a front separator (90) and a rear separator (95) disposed at the front and rear sides, respectively, in the direction of the axial line (O) and joined to each other, the front separator (90) having a first locking portion having a rear surface (90s1, 90s2), the rear separator (95) having a second locking portion having a front surface (95s); and wherein the metal terminal member (20, 30, 40, 50) is held between the front separator (90) and the rear separator (95) such that the front locking portion (29, 35f, 59) abuts the rearward facing surface (90s1, 90s2), and the front locking portion (29, 35f, 59) is thereby in locking engagement with the rearward facing surface (90s1, 90s2), and the rear locking portion (45e, 58e) is in locking engagement with the forward facing surface (95s).The gas sensor (1) according to claim 1, wherein a contact point (P1, P2) at which the metal terminal member (20, 30, 40, 50) comes into contact with the electrode pad (11a) is disposed between the rearward facing surface (90s1, 90s2) and the forward facing surface (95s).The gas sensor (1) according to claim 1 or 2, wherein the metallic terminal member (20, 30, 40, 50) is composed of a front metallic terminal member (20, 30) and a rear metallic terminal member (40) that are disposed at the front and rear sides, respectively, and are connected to each other, wherein the front metallic terminal member (20, 30) includes the front locking portion (29, 35f), and wherein the rear metallic terminal member (40) includes the rear locking portion (45e); wherein the rear metallic terminal member (40) is connected to the lead wire (146) and is at least partially accommodated in the rear separator (95); and wherein the front metallic terminal member (20, 30) is in contact with the electrode pad (11a) and is at least partially accommodated in the front separator (90).The gas sensor (1) according to claim 3, wherein a front end portion (43) of the rear metal terminal member (40) takes the shape of at least a part of a circular column or a cylindrical tube, the front metal terminal member (20, 30) having, at its rear end, a connection portion (23, 33) taking the shape of at least a part of a cylindrical tube, and the front end portion (43) being fitted into the connection portion (23, 33).A method for manufacturing a gas sensor (1) comprising: a sensor element (10) having a plate shape extending in an axial line (O) direction and having an electrode pad (11a) on an outer surface of a rear end portion thereof; a metallic terminal element (20, 30, 40, 50) extending in the axial line (O) direction and electrically connected to the electrode pad (11a); a tubular separator (90, 95) holding the metallic terminal element (20, 30, 40, 50) and surrounding the rear end portion of the sensor element (10); and a lead wire (146) connected to a rear end portion of the metallic terminal element (20, 30, 40, 50) and extending to behind the separator (90, 95), the metallic terminal element (20, 30, 40, 50) having a front locking portion (29, 35f, 59 ) and a rear locking portion (45e, 58e) provided on the front and rear end sides, respectively, of the terminal metal member, the separator (90, 95) is composed of a front separator (90) and a rear separator (95) disposed on the front and rear sides, respectively, in the direction of the axial line (O) and joined to each other, the front separator (90) having a first locking portion having a rear surface (90s1, 90s2), the rear separator (95) having a second locking portion having a front surface (95s), the method comprising a step of disposing the front separator (90) and the rear separator (95) on the front and rear sides, respectively, of the terminal metal member (20, 30, 40, 50) and holding the terminal metal member (20, 30, 40, 50), 50) between the front separator (90) and the rear separator (95), such that the front locking portion (29, 35f, 59) abuts the rearward facing surface (90s1, 90s2), and the front locking portion (29, 35f, 59) is thereby lockingly engaged with the rearward facing surface (90s1, 90s2), and the rear locking portion (45e, 58e) is lockingly engaged with the forward facing surface (95s).

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