JP2009063591A - Oxygen sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxygen sensor for achieving high reliability and a product life by preventing the occurrence of chipping or cracking on the bottom face outer edge of a separator during assembly to avoid the conditions of poor or impossible operation while sufficiently securing the strength of the separator. <P>SOLUTION: A heating element end storage hole 72e has a bottom face 18e, and a lead wire insertion hole 18a2 is communicated with the heating element end storage hole 72e in the peripheral direction. In the direction perpendicular to an axis O2 of the separator 18, a clearance forming part S which forms a fixed-distance clearance between a heater terminal 3b and the bottom face outer edge 18e1 of the separator 18 is formed on the heater terminal 3b and/or the separator 18. With the clearance forming part S formed on at least one of the heater terminal 3b and the separator 18, contact/interference between the heater terminal 3b and the bottom face outer edge 18e1 is prevented when inserting and assembling the rear end of the heating element 3 into the heating element end storage hole 72e. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an oxygen sensor for detecting oxygen in a gas to be measured such as an exhaust gas of an internal combustion engine.

  As one form of such an oxygen sensor, an oxygen sensor having a hollow shaft shape with a closed front end and an oxygen detecting element that is directed to a gas to be measured on the front end side is known. In this type of oxygen sensor, the atmosphere as a reference gas is introduced into the inner surface of the oxygen detection element, while the outer surface of the oxygen detection element is in contact with the exhaust gas to be measured. Oxygen concentration cell electromotive force is generated according to the difference in oxygen concentration between the inner and outer surfaces. The oxygen concentration cell electromotive force is taken out from the inner and outer surfaces as a detection signal of the oxygen concentration in the exhaust gas via a lead wire or the like, whereby the oxygen concentration in the exhaust gas can be detected.

  In this type of oxygen sensor, when the exhaust gas temperature is low, such as immediately after the engine is started, the activity of the oxygen detection element constituted by the solid electrolyte member is not sufficient, and it takes a considerable time to obtain a measurable electromotive force. . Therefore, a shaft-like heating element with a heat generating part is inserted into the hollow part of the oxygen detection element, and the oxygen detection element is heated and activated at the time of engine start-up, thereby quickly measuring at the time of start-up with relatively many harmful components. The output (electromotive force) is raised.

  By the way, in order to efficiently transmit the amount of heat generated in the heating element to the oxygen detection element and to activate the rising of the oxygen detection element, oxygen that makes the heating part of the heating element contact the inner wall surface of the hollow part of the oxygen detection element A sensor may be configured. In the oxygen sensor having such a configuration, in order to bring the heat generating part of the heat generating element into contact with the inner wall surface of the hollow part of the oxygen detecting element, for example, the central axis of the heat generating element is installed inclined with respect to the central axis of the oxygen detecting element. Sometimes. As a result, the heating element is arranged eccentrically so that the central axis of the heating element is closer to one side with respect to the central axis of the oxygen detection element.

  On the other hand, in order to facilitate positioning of the heating element during assembly and reduce the total length of the oxygen sensor, a separator disposed on the rear side of the oxygen detection element is formed with a heating element end receiving hole having an open front end surface, In some cases, the rear end surface of the heat generating element (hereinafter referred to as the heat generating element end surface) is brought into contact with the bottom surface of the heat generating element end portion accommodation hole (hereinafter referred to as the separator bottom surface). At this time, as described above, if the central axis of the heating element is inclined with respect to the central axis of the oxygen detecting element or is eccentric so as to be closer to one side, When inserting and assembling the end portion, the heater terminal extending from the rear end side of the heating element easily contacts and interferes with the outer edge of the separator bottom surface (hereinafter referred to as the bottom surface outer edge). The contact / interference causes chipping (cracking), cracks, etc. at the outer edge of the bottom surface, and these fallen fragments may cause the oxygen sensor (oxygen detection element) to malfunction or become inoperable. Even if the heating element and the separator are not eccentric in design, the same situation may occur due to a manufacturing error, a non-uniform pushing force during assembly, or the like.

  Therefore, by making the bottom surface of the separator narrow (that is, keeping the area of the bottom surface of the separator small), contact / interference of the heater terminal with the outer edge of the bottom surface can be avoided. However, since the central skeleton formed in a shape including the central axis of the separator and the bottom surface of the separator is thinned, the strength of the separator may be insufficient. For example, if the bottom surface of the separator comes into contact with the end face of the heating element and is repeatedly subjected to vibrations or the like during operation of the internal combustion engine, fatigue failure or the like is likely to occur in the central skeleton portion of the separator in a relatively short period of time.

  Accordingly, an object of the present invention is to prevent the occurrence of chipping and cracking at the outer edge of the bottom surface of the separator during assembly while ensuring sufficient strength of the separator, avoiding malfunctions and inoperability, and providing high reliability. It is to provide an oxygen sensor that can realize the product life.

Means and actions / effects for solving the problems

In order to solve the above problems, the oxygen sensor of the present invention is
The front end portion has a closed hollow shaft shape, and the front end portion side is directed to the gas to be measured, and an oxygen detection element,
An axial heating element that is disposed in a hollow portion of the oxygen detection element and heats the oxygen detection element;
A separator having a heating element end accommodating hole that is disposed substantially coaxially with the hollow portion on the rear side of the oxygen detection element, has a front end surface opened, and a rear end portion of the heating element is inserted;
The heating element end accommodating hole has a bottom surface at an intermediate position in the axial direction of the separator, and a heater terminal extended from the rear end side of the heating element inserted into the heating element end accommodating hole, A lead wire insertion hole allowing insertion of a connected lead wire is communicated with the heating element end accommodating hole in the circumferential direction,
And, in order to prevent the heater terminal inserted through the lead wire insertion hole from contacting and interfering with the bottom surface outer edge, in a direction orthogonal to the axis, between the heater terminal and the bottom surface outer edge. A gap forming portion for forming a certain amount of gap is formed in the heater terminal and / or the separator.

  According to the present invention, the heating element end accommodation hole has a bottom surface, and the lead wire insertion hole communicates with the heating element end accommodation hole in the circumferential direction, and in a direction orthogonal to the axis of the separator, A gap forming portion that forms a certain amount of gap between the heater terminal and the bottom edge of the separator is formed in the heater terminal and / or the separator. By forming a gap forming part in at least one of the heater terminal and separator, contact / interference between the heater terminal and the outer edge of the bottom surface is prevented when inserting and assembling the rear end of the heating element into the heating element end receiving hole. can do. Therefore, chipping and cracks are less likely to occur on the outer edge of the bottom surface of the separator, and these falling pieces can prevent the oxygen sensor (oxygen detection element) from malfunctioning or becoming inoperable. And can increase the product life. Thus, in the present invention, for example, in order to bring the heating element into contact with the inner wall surface of the hollow portion of the oxygen detection element, the central axis of the heating element is inclined with respect to the central axis of the oxygen detection element. This is particularly effective in the case of being arranged eccentrically so as to be closer to one side with respect to the latter.

  In addition, by forming a gap forming portion in at least one of the heater terminal and the separator, the strength of the separator is reduced when the area of the bottom surface of the separator is reduced and the central skeleton portion of the separator need not be thinned. There is nothing. Therefore, even when the separator bottom surface is in contact with the end face of the heating element and repeatedly receives vibration during operation of the internal combustion engine, fatigue damage or the like hardly occurs in the central skeleton portion of the separator for a long time.

  Here, when the lead wire insertion hole penetrates the separator in the axial direction and the front end side in the axial direction communicates with the heating element end accommodation hole at the outer edge of the bottom surface and is integrated with the heating element end accommodation hole The operation of inserting the heating element and the heater terminal into the integrated heating element end receiving hole and the lead wire insertion hole is simplified, and this makes contact and interference between the heater terminal and the outer edge of the bottom surface more unlikely.

  And the said clearance gap formation part is formed in the heater terminal by which the base end part was fixed to the rear end side of a heat generating body, and the expansion part which expands continuously or stepwise in the radial direction outer side with respect to a bottom face outer edge, can do. As a result, the heater terminal that expands radially outward by matching the positional relationship between the heating element end receiving hole and the lead wire insertion hole and the shape of the heater terminal without contacting or interfering with the outer edge of the bottom surface of the separator. It can be smoothly inserted into the lead wire insertion hole from the heat generating element end accommodating hole. When the gap forming portion is not formed on the separator side, it is desirable that the expanded portion of the heater terminal is plastically deformed before insertion into the lead wire insertion hole.

  Further, the gap forming portion can be a chamfered portion that is provided on the outer edge of the bottom surface of the separator and has a predetermined inclination with respect to the axis. Since the outer edge of the bottom surface of the separator is formed to have a small diameter by the amount of the chamfered portion, the heater terminal is less likely to contact and interfere with the outer edge of the bottom surface. In addition, by chamfering the outer edge of the bottom surface of the separator that is likely to cause chipping, cracking, etc., and easily fall off, it is possible to effectively prevent these occurrences and the scattering of the falling pieces. Furthermore, there are also advantages in the manufacturing process as follows. In other words, when the molded body of the separator is manufactured by die molding, the variability caused by the fact that the mating surface of the mandrel that forms the heating element end receiving hole and the mandrel that forms the lead wire insertion hole is located on the outer edge of the bottom surface of the separator. This can be prevented by chamfering the outer edge of the bottom surface.

  Next, in the central skeleton portion of the separator surrounded by the bottom surface of the heating element end portion receiving hole and the lead wire insertion hole, the gap forming portion is inserted into the lead wire insertion hole from the central skeleton portion in a direction intersecting the axis. It can be a convex part protruding in While the heater terminal is supported by this convex part, it can be smoothly inserted into the lead wire insertion hole in a state separated from the outer edge of the bottom surface, and at this time, the convex part is accompanied by insertion of the heater terminal into the lead wire insertion hole. It has a function as a jig for gradually expanding the heater terminal. In this case, it is desirable that the heater terminal be elastically deformed by insertion into the lead wire insertion hole.

  Further, this gap forming portion is formed in the heater terminal, extends in a predetermined direction from one end, and a tongue piece located inside the cut extending from the one end to the other end in the insertion direction of the heating element. It can be an elastic support in the form of a trigger. Because the heater terminal is securely held in the lead wire insertion hole by this elastic support part, the heater terminal jumps out of the lead wire insertion hole due to the pushing force during assembly or vibration during internal combustion engine operation, etc. Etc. can be prevented. Then, in order to more smoothly insert the elastic support portion into the lead wire insertion hole, the support shaft is positioned on the rear side in the axial direction of the separator, and the tongue piece located on the front side of the support shaft is generated. It is desirable to form. The heater terminals other than the elastic support portion may be plastically deformed in advance before being inserted into the lead wire insertion hole, or may be elastically deformed by being inserted into the lead wire insertion hole.

  By the way, when the separator bottom face and the heating element end face are arranged to face each other, and at least one of the separator bottom face and the heating element end face has a protruding surface that protrudes in a form in which the tip side continuously reduces in cross section in the facing direction. There is. The projecting surfaces are arranged opposite to each other, and can prevent chipping, cracks, and the like from occurring on the bottom surface of the separator and the end surface of the heating element, which can be brought into contact with each other by a pushing force during assembly or vibration during internal combustion engine operation. .

  Here, when the bottom surface of the separator and the end surface of the heating element that face each other are in contact, it is desirable that they contact in a point-like contact state at the tip of the projecting surface. The occurrence of chipping, cracks and the like on the body end surface can be suppressed. In addition, as described above, since the strength of the separator can be sufficiently secured by forming the gap forming portion, even if the separator bottom surface comes into contact with the end surface of the heating element and is repeatedly subjected to vibration during operation of the internal combustion engine, In the central skeleton, fatigue failure or the like hardly occurs for a long time. In the present specification, the point-like contact state refers to a point contact or a state approximate thereto.

Hereinafter, embodiments of the present invention will be described based on examples shown in the drawings.
FIG. 1 shows an internal structure of an embodiment of an oxygen sensor according to the present invention, and FIG. 2 is an enlarged view of a main part. The oxygen sensor 1 includes a hollow shaft-shaped oxygen detection element 2 whose tip is closed, and a heating element 3 inserted into the hollow portion 2a of the oxygen detection element 2. The oxygen detection element 2 is formed in a hollow shaft shape by a solid electrolyte having oxygen ion conductivity. A typical example of such a solid electrolyte is ZrO _{2 in} which Y ₂ O ₃ or CaO is dissolved, but other alkaline earth metal or rare earth metal oxides and ZrO ₂ are used. A solid solution may be used. Furthermore, HfO ₂ may be contained in the ZrO ₂ as a base. As shown in FIGS. 2 and 3, the inner surface of the hollow portion 2a of the oxygen detecting element 2 has an internal electrode layer 2c formed porous, for example, of Pt or a Pt alloy so as to cover almost the entire surface. On the other hand, external electrode layers 2b are similarly provided on the outer surface so as to cover the front portion thereof. In addition, a cylindrical metal casing 10 is provided outside the intermediate portion of the oxygen detecting element 2 via insulators 6 and 7 made of insulating ceramic and ceramic powder 8 made of talc. In the following description, the side (closed side) toward the tip end in the axial direction of the oxygen detection element 2 is referred to as “front side”, and the side toward the opposite direction is referred to as “rear side”.

  The casing 10 includes a metal shell 9 having a threaded portion 9b for attaching the oxygen sensor 1 to an attachment portion such as an exhaust pipe, and a protector 11 attached so as to cover a front opening of the metal shell 9. The oxygen sensor 1 of the present embodiment is used in such a manner that the front side of the screw portion 9b is located in the engine such as an exhaust pipe, and the rear side thereof is located in the outside atmosphere. The metal shell 9 (casing 10) holds the oxygen detection element 2 in a state in which the front end side (detection part) of the oxygen detection element 2 is projected from the front opening so as to be directed to the exhaust gas to be measured. At the same time, a cap-like protector 11 is attached to a cylindrical protector attachment portion 9a formed in the opening, and covers the detection portion of the oxygen detection element 2 with a predetermined space therebetween. The protector 11 is formed with a plurality of gas permeation ports 12 through which exhaust gas permeates.

  A rear portion of the metal shell 9 is crimped between the insulator 6 and the insulator 15 via a ring 15, and an opening 16 </ b> F (see FIG. 6) formed at the front end of the cylindrical metal outer cylinder 16 in the metal shell 9. ) Is fitted from the outside. An all-around laser welded portion 16E formed along the circumferential direction of the metal shell 9 joins and fixes the inner peripheral surface of the front end opening 16F of the outer cylinder 16 and the outer peripheral surface of the metal shell 9. The rear end opening 16R of the outer cylinder 16 is sealed by fitting a grommet 17 made of rubber or the like, and a ceramic separator 18 (hereinafter simply referred to as a separator) is provided on the front side. It has been. The detection element side lead wires 20 and 21 and the heating element side lead wires 19 and 22 are arranged so as to penetrate the ceramic separator 18 and the grommet 17 (see FIG. 7).

  The ceramic separator 18 is provided substantially coaxially with the casing 10 on the rear side of the casing 10. The outer cylinder 16 has a cylindrical shape in which the front end opening portion 16F is connected to the casing 10 so as to be substantially coaxially overlapped from the rear outer side in a state of covering the ceramic separator 18 from the outside. The grommet 17 is positioned on the rear side of the ceramic separator 18 and is elastically fitted inside the rear end opening 16R of the outer cylinder 16.

Next, one lead wire 21 of the detection element side lead wires 20, 21 is a first terminal fitting 23 having a connector 23a, a lead wire portion 23b, a fixing portion 23c, and a downward pressing portion 23d that are integrally formed with each other. It is electrically connected to the internal electrode layer 2c (FIG. 2) of the oxygen detecting element 2 through the (pressing member). The other lead wire 20 passes through a second terminal fitting 33 having a connector 33a, a lead wire portion 33b, and a fitting main body portion 33c that are integrally formed with each other, and then the external electrode layer 2b of the oxygen detection element 2 (FIG. 3). ) And are electrically connected. The oxygen detection element 2 is activated by heating with the heating element 3 disposed inside thereof. The heating element 3 is a rod-shaped ceramic heater, and a heating part 3a having a resistance heating element (not shown) in a core material mainly composed of Al ₂ O _{3 is connected} to heater terminals 3b and 3b on the positive electrode side and the negative electrode side. The front end portion (detection portion) of the oxygen detection element 2 is heated by energization through the heating element side lead wires 19 and 22 (FIG. 7) connected to the oxygen detection element. The detection element side lead wires 20 and 21 and the heating element side lead lines 19 and 22 include two detection element side lead wire insertion holes 18a1 and 18a1 and heating element side lead wires that are provided penetrating in the axial direction of the ceramic separator 18. Insertion holes 18a2 and 18a2 (lead wire insertion holes), two detection element side lead wire insertion holes 17a1 and 17a1, and heating element side lead wire insertion holes 17a2 and 17a2 provided penetrating in the axial direction of the grommet 17. Are respectively inserted and drawn out to the outside.

  As shown in FIGS. 2 and 3, the first terminal fitting 23 presses the outer surface of the heating element 3 with the inner surface of the lower pressing portion 23d formed on the distal end side, and at least the distal end portion of the heating element 3 is moved to the oxygen detecting element. 2 is brought into contact with the inner wall surface of the hollow portion 2a. The outer surface of the fixing portion 23c following the downward pressing portion 23d is fitted into the inner surface of the oxygen detection element 2, thereby fixing the position of the first terminal fitting 23 in the axial direction. Further, one end of the lead wire portion 23b is integrated so as to be connected to one place in the circumferential direction of the fixed portion 23c, and the connector 23a is integrated to the other end. In the upper part (rear part) of the fixing part 23c, a U-shaped cut is provided in a part of the peripheral surface of the fixing part 23c in the vicinity of the left and right edges of the opening provided in the fixing part 23c. Is folded inward in the radial direction to form a pair of left and right upper pressing portions 23e. Reference numeral 23g denotes a hook for preventing the fixing portion 23c from entering the heating element end accommodating hole 18c.

  On the other hand, the second terminal fitting 33 has a cylindrical fitting main body portion 33c, and is integrated in such a manner that one end of the lead wire portion 33b is connected to one circumferential position of the fitting main body portion 33c, and further to the other end. The connector 33a is integrated. On the other hand, an axial slit 33e is formed on the side opposite to the connection point of the lead line portion 33b across the central axis. The rear end portion of the oxygen detection element 2 is inserted into the metal fitting main body portion 33c from the inside in such a manner as to elastically push it. Specifically, a conductive layer 2 f as an external output extraction portion is formed in a strip shape along the circumferential direction at the rear end portion of the outer peripheral surface of the oxygen detection element 2. The external electrode layer 2b covers the entire surface of the main part on the front end side of the engagement flange portion 2s of the oxygen detection element 2 by, for example, electroless plating. On the other hand, the conductive layer 2f is formed, for example, by pattern formation / baking using a metal paste, and is electrically connected to the external electrode layer 2b via the axially formed connection pattern layer 2h. Yes.

  As shown in FIG. 4, the heating element 3 is pressed by the lower pressing part 23d and the upper pressing part 23e in a direction intersecting the central axis O2 of the hollow part 2a of the oxygen detecting element 2, and the central axis O1 of the heating element 3 is oxygenated. The detection element 2 is arranged eccentrically (offset) so as to be closer to one side with respect to the central axis O2 of the hollow part 2a of the detection element 2, and at least a part of the heating element 3 contacts the inner wall surface of the hollow part 2a of the oxygen detection element 2. is doing.

  FIG. 5 shows the outer cylinder 16. The outer cylinder 16 is divided into two front and rear in the axial direction, and the rear cylinder member 162 on the rear side of the outer cylinder side support part 16A formed at the rear part of the front outer cylinder member 161 located on the front side is arranged. The front part is overlapped and connected substantially coaxially from the rear outside. In this overlapping connecting portion, an all-around laser welded portion 16C that joins the outer peripheral surface of the outer cylinder side support portion 16A of the first outer cylinder member 161 and the front inner peripheral surface of the second outer cylinder member 162 is a connecting portion. It is formed along the circumferential direction. The front end opening 16F of the outer cylinder 16 is connected to the metal shell 9 so as to be substantially coaxially overlapped from the rear outer side, and the front end opening 16F inner peripheral surface of the outer cylinder 16 and the outer peripheral surface of the metal shell 9 are connected. The all-around laser welded portion 16E to be joined is formed along the circumferential direction of the metal shell 9.

  Next, the outer cylinder side support part 16A formed at the rear part of the front outer cylinder member 161 will be described with reference to FIG. The outer cylinder side support portion 16A as a whole has a tapered shape whose outer diameter decreases toward the rear side, and this shape is realized by the following configuration. In the outer cylinder side support portion 16A, two reduced diameter portions having a form that decreases in an inclined manner as the outer diameter goes rearward are formed on the front and rear in the axial direction. Between the first reduced diameter portion 16a1 formed on the front side of the two reduced diameter portions and the second reduced diameter portion 16a2 formed on the rear side, the front side cylinder is substantially parallel to the axis. A shaped portion 16b1 is formed. The front inner peripheral surface of the rear outer cylindrical member 162 is overlapped and connected to the outer peripheral surface of the first cylindrical portion 16b1 from the rear outer side, and the all-around laser welded portion 16C is formed along the circumferential direction of the connecting portion. Has been.

  Moreover, the 2nd cylindrical part 16b2 is formed in the form which follows the outer peripheral surface of the main-body part 18B of the separator 18 in the back side rather than the 2nd diameter reduction part 16a2. Further, the rear side of the second cylindrical portion 16b2 is bent radially inward to form a bent portion 16c, and the rear support surface 16c1 of the bent portion 16c is supported on the front side of the separator side support portion 18A. The surface is in contact with the surface 18A1. The bent portion 16c formed in this way serves as a catch for the front side support surface 18A1 of the separator side support portion 18A when the main body portion 18B of the separator 18 is disposed inside the outer cylinder side support portion 16A. Function. The rear side support surface 16c1 of the bent part 16c is bent inward in the radial direction, and serves as a guide when the main body part 18B of the separator 18 is inserted into the outer cylinder side support part 16A. Yes.

  As described above, the outer cylinder side support portion 16A includes the first and second reduced diameter portions 16a1 and 16a2, the first and second cylindrical portions 16b1 and 16b2, and the bent portion 16c. When the outer cylinder side support portion 16A supports the separator side support portion 18A from below, the inner peripheral surface of the outer cylinder side support portion 16A is the space formed between the outer peripheral surface of the main body portion 18B of the separator 18 and the two. It is provided so as to enclose part S3 (see FIG. 2). Therefore, the impact force caused to the outer cylinder 16 by the spring stone or the like is attenuated by the spring effect by the two reduced diameter portions 16a1 and 16a2 and the isolation effect by the space portion S3 and transmitted to the separator 18. Can be prevented.

  On the other hand, the rear side outer cylinder member 162 has a grommet 17 inserted inside the rear end opening 16R, and the front side of the grommet 17 insertion portion is inclined (continuously) larger as the inner diameter becomes frontward. The enlarged diameter part 16B which has the form which becomes is provided. The inner peripheral surface of the rear end opening 16R of the rear side outer cylinder member 162 is used as an insertion guide for the outer peripheral surface of the separator side support portion 18A.

  The wall thickness t1 of the outer cylinder member 161 provided on the front side is set to the rear side in consideration of the impact resistance against the rock and the heat transfer amount to the grommet side (rear side). The thickness is equal to or greater than the thickness t2 of the rear side outer cylinder member 162 provided on the rear side. That is, the front-side outer cylinder member 161 on the front side (detection element side) that is often in a low position during attachment and has a high probability of hitting a rock is relatively thick and has high impact resistance. On the other hand, the second outer cylinder member 162 on the rear side close to the attachment position of the grommet 17 is relatively thin and reduces the amount of heat transfer to the grommet 17 side (rear side). Specifically, the thickness t1 of the front outer cylinder member 161 is 0.5 mm or more and 0.8 mm or less (for example, 0.6 mm), and the wall thickness t2 of the rear outer cylinder member 162 is 0.3 mm or more and 0. It is desirable that it is 5 mm or less (for example, 0.3 mm).

  In FIG. 2, an annular gap S <b> 0 having a radial interval of, for example, 0.3 mm or more is provided between the outer peripheral surface of the separator-side support portion 18 </ b> A and the inner peripheral surface of the rear-side outer cylinder member 162. The gap S <b> 0 forms an annular space for preventing the impact force that is brought to the outer cylinder 16 by the jumping stone or the like from being directly transmitted from the outer cylinder 16 to the separator 18. On the other hand, a small radial gap S1 is formed between the edge of the bent portion 16c of the outer cylinder side support portion 16A and the outer peripheral surface of the main body portion 18B of the ceramic separator 18. The gap S1 is a guide margin provided for smoothly inserting the main body portion 18B of the ceramic separator 18 into the outer cylinder side support portion 16A without rattling.

  FIG. 6 shows details of the ceramic separator 18. In the main body 18B of the ceramic separator 18 having a circular cross section perpendicular to the axis, two detection element side lead wires 20 and 21 and two heating element side lead wires 19 and 22 (see FIG. 7) are inserted. Detection element side lead wire insertion holes 18a1 and 18a1 and heating element side lead wire insertion holes 18a2 and 18a2 (hereinafter, collectively referred to as insertion holes 18a) are formed to penetrate in the axial direction. On the outer peripheral surface on the rear end side in the axial direction, a separator-side support portion 18A having a flange-like shape and a circular shape orthogonal to the axis is formed so as to integrally protrude outward over the entire circumference. The front-side support surface 18A1 of the separator-side support portion 18A is formed as an inclined surface whose outer diameter increases toward the rear side. On the rear end surface of the ceramic separator 18 (separator-side support portion 18A), the ventilation groove 18b is formed in a cross shape and in a direction perpendicular to the axis at a position where it does not interfere with the four insertion holes 18a. The ventilation groove 18b communicates with the gap K between the detection element side lead wire insertion holes 18a1, 18a1 and the detection element side lead wires 20, 21 (see FIG. 2).

  The ceramic separator 18 has four insertion holes 18a from the rear end side (the upper end side in FIGS. 6C and 6D) at intervals of approximately 90 ° along the pitch circle P centered on the central axis O2. It penetrates in the axial direction. Further, a terminal accommodating hole 72 is formed from the front end in the axial direction of the ceramic separator 18 (the lower end in FIGS. 6C and 6D) to the bottom surface 18e located at the substantially central portion of the entire length along the axial direction. The terminal accommodating hole 72 includes a first accommodating portion 72b, a second accommodating portion 72c, two heater terminal accommodating portions 72d and 72d, and a central communication portion 72e (a heating element end accommodating hole). The first accommodating portion 72b and the second accommodating portion 72c insert and hold the first connecting fitting 23 and the second connecting fitting 33 from the front side to the rear side, respectively, while the heater terminal accommodating portions 72d and 72d are + The pole-side and -pole-side heater terminals 3b and 3b are inserted and held from the front side to the rear side, respectively. The central communication portion 72e is located in the middle of the four storage portions 72b, 72c, 72d, and 72d, and is formed in a communication form with each of the storage portions. Specifically, the first and second accommodating portions 72b and 72c and the heater terminal accommodating portions 72d and 72d are in a state of facing each other with the central communication portion 72e interposed therebetween, and are arranged at approximately 90 ° intervals along the pitch circle P. It has the same positional relationship as the insertion hole 18a.

  The first accommodating portion 72b, the second accommodating portion 72c, and the two heater terminal accommodating portions 72d and 72d are each formed with a narrow opening facing the central communicating portion 72e and an outer peripheral direction opposite to the central communicating portion 72e ( It is formed as a space surrounded by a partition wall 18c having a wide bottom portion extending in the depth direction and an inclined portion in which the opening width (inter-wall distance) is gradually increased from the opening portion to the bottom portion and the both are continuously provided. (See FIG. 6B). Each of the accommodating portions 72b, 72c, 72d, and 72d has a shell shape in which a part thereof is opened to the central communication portion 72e, and has a shape close to a fan.

  Further, as shown in FIG. 6B, the rear end edge of the metal fitting body 33 c of the second connection fitting 33 is the front end of the partition wall 18 c on the opening side end face (front end face) of the terminal accommodating hole 72 of the ceramic separator 18. It is in contact with the surface. On the other hand, the rear end edge of the metal fitting main body portion 23 c of the first connection fitting 23 is in contact with the front end surface of the partition wall 18 c on the inner side of the metal fitting main body portion 33 c and the pitch circle P of the second connection fitting 33. Further, the partition walls 18c formed between the adjacent insertion holes 18a are formed so as to protrude inward from the pitch circle P. The central communication portion 72e has an inner diameter larger than the outer diameter of the heating element 3 and also serves as a heating element end accommodating hole, and the rear end surface 3c (heating element end surface) of the heating element 3 has a terminal accommodating hole. It is inserted from the front end side of 72 until it contacts the bottom surface 18e (separator bottom surface) along the axis. This facilitates the positioning of the heating element 3 in the axial direction during assembly, reduces the overall length of the oxygen sensor 1, and realizes a compact sensor size.

  By the way, in the front half part of the ceramic separator 18, when viewed from the front end side (FIG. 6B), the four insertion holes 18a overlap with (include in) the terminal accommodating holes 72 inside the pitch circle P. ) And integrated. Specifically, the front end side in the axial direction of each insertion hole 18a opens to the central communication portion (heating element end accommodation hole) 72e at the outer edge 18e1 of the bottom surface 18e, and overlaps and integrates with the central communication portion 72e. To do. On the other hand, in the latter half of the ceramic separator 18, a central skeleton that rises in a columnar shape (for example, a columnar shape, a polygonal columnar shape, etc.) that includes the central axis O2 and is surrounded by the four insertion holes 18a and the bottom surface 18e. A portion 18f is formed. That is, the bottom surface 18e forms the tip surface of the central skeleton portion 18f.

  FIG. 7 shows an assembled state of the grommet 17 and the ventilation portion 53. The grommet 17 has two detection element side lead wire insertion holes 17a1 and 17a1 and heating element side lead wire insertion holes 17a2 and 17a2 for inserting the detection element side lead wires 20 and 21 and the heating element side lead wires 19 and 22, respectively. (Hereinafter, when these are collectively referred to as an insertion hole 17a), an inside thereof is provided penetrating in the axial direction. A central through hole 17b is provided in the central portion in the radial direction of the grommet 17, and a ventilation portion 53 is fitted into the central through hole 17b. The insertion hole 17a, the central through hole 17b, and the outer peripheral surface 17A of the grommet 17 seal between the outer surface of the ventilation portion 53 and the lead wires 19, 20, 21, and 22 and the inner wall of the rear end opening 16R of the outer cylinder 16. . By providing the ventilation part 53 in the grommet 17, it becomes easy to provide the ventilation part 53 at a relatively high position, and it is difficult for water droplets to enter and the waterproofness is improved.

  The ventilation part 53 includes a filter 53A and a filter support fitting 53B. The filter 53A has a cylindrical peripheral surface portion 53A1 extending in the axial direction, and a ventilation end surface portion 53A2 that is connected to the peripheral surface portion 53A1 in a lid shape at the rear end portion and guides outside air in the axial direction, and is entirely axial. The cross section has an inverted U shape. The cylindrical filter support fitting 53B has a flange portion 53B2 at the front end, the cylindrical peripheral surface portion 53B1 extending in the axial direction is fitted into the cylindrical peripheral surface portion 53A1 of the filter 53A, and the filter 53A is placed inside. The cylindrical peripheral surface portion 53A1 of the filter 53A is supported so as not to be broken when the small diameter portion 16c of the outer cylinder 16 is swaged to form the grommet swaged portion 16B. By providing the grommet 17 with the ventilation part 53 such as the filter 53A, the ventilation part 53 can be kept as far as possible from the detection part of the oxygen detection element 2 which is the part exposed to the highest temperature in the oxygen sensor 1, and the filter 53A It is advantageous for heat resistance.

  The filter 53A or the filter support metal fitting 53B can be provided with an inclination such as a taper along the axial direction on the inner and outer peripheral surfaces, respectively, so that the fitting can be strengthened. The filter 53A can be rotated 180 ° from the state shown in FIG. 7 so that the ventilation end surface portion 53A2 is positioned at the bottom (front end portion). However, in order to prevent water and the like from entering, the rear end surface and the ventilation end surface of the grommet 17 The state of FIG. 7 where the portion 53A2 is substantially flush is more desirable. The filter 53A is made of, for example, polytetrafluoroethylene (PTFE) porous fiber structure (trade name: Gore-Tex (Japan Gore-Tex Co., Ltd.)), etc. Is configured as a water-repellent filter that blocks air and / or gas such as water vapor.

  In the oxygen sensor 1, the atmosphere as the reference gas is the ventilation end surface portion 53A2 (venting portion) of the filter 53A → the venting groove 18b of the ceramic separator 18 → the detecting element side lead wire insertion holes 18a1, 18a1 and the detecting element side lead wire 20, 21 is introduced into the inner surface (internal electrode layer 2c) of the oxygen detection element 2 through the gap K → the hollow portion 2a (see arrow R in FIG. 2). On the other hand, the exhaust gas introduced through the gas permeation port 12 of the protector 11 is in contact with the outer surface (external electrode layer 2b) of the oxygen detection element 2, and the oxygen detection element 2 has an oxygen concentration difference between its inner and outer surfaces. Accordingly, an oxygen concentration cell electromotive force is generated. Then, the oxygen concentration cell electromotive force is used as a detection signal of the oxygen concentration in the exhaust gas from the inner and outer electrode layers 2c and 2b (FIGS. 2 and 3) to the first and second terminal fittings 23 and 33 and the detection element side lead wire. The oxygen concentration in the exhaust gas can be detected by taking it out through 21 and 20.

  FIG. 8 is a longitudinal sectional view of the first embodiment showing the assembled state of the ceramic separator 18 and the heating element 3. The separator bottom face 18e and the heating element end face 3c are arranged in opposition to each other at the central communication portion 72e. Among these, the separator bottom face 18e is formed with a protruding surface F1 that protrudes in a spherical shape toward the planar heating element end face 3c side. Has been. As a result, the separator bottom surface 18e and the heating element end surface 3c come into contact with each other in a point-like contact state at the tip of the projecting surface F1, and the contact area becomes small. Therefore, chipping, cracks, and the like hardly occur on these surfaces. .

  In the heater terminal 3b, an intermediate portion following the base end portion 3b1 fixed to the rear end side of the heating element 3 expands stepwise (for example, an L-shaped crank shape) radially outward from the bottom surface outer edge 18e1 of the separator 18. Opened to form an expanded portion 3b2. The expanded portion 3b2 forms a predetermined gap between the heater terminal 3b and the bottom surface outer edge 18e1 in a direction orthogonal to the central axis O2 of the separator 18. This clearance prevents contact / interference between the heater terminal 3b and the bottom outer edge 18e1, and the heater terminal 3b is smoothly inserted into the heater terminal accommodating portion 72d and the heating element side lead wire insertion hole 18a2. It has a function as the formation part S. If the expanded portion 3b2 of the heater terminal 3b is plastically deformed by a process such as bending before the insertion step, the assembling work can be performed efficiently.

  In FIG. 9, the 2nd Example of the assembly | attachment state of the ceramic separator 18 and the heat generating body 3 is shown. In this embodiment, a projecting surface F1 projecting in a spherical shape toward the separator bottom surface 18e side is formed on the heating element end surface 3c, and a spherical concave surface F2 corresponding to the projecting surface F1 is formed on the separator bottom surface 18e. ing. And the curvature radius R2 of the concave surface F2 formed in the separator bottom face 18e is made larger than the curvature radius R1 of the protrusion surface F1 formed in the heat generating body end surface 3c, and it has the structure of a pivot bearing shape. As a result, the end face 3c of the heating element and the separator bottom face 18e can smoothly rotate relative to each other, and the twisting between the heating element 3 and the separator 18 is less likely to occur.

  A chamfer 18e2 having a predetermined inclination with respect to the central axis O2 is provided on the outer edge 18e1 of the separator bottom surface 18e, and a gap forming portion S is formed. Contact / interference between the heater terminal 3b and the bottom outer edge 18e1 can be prevented, and the occurrence of chipping, cracks, etc. and the scattering of falling pieces can be prevented. Furthermore, there are also advantages in the manufacturing process as follows. That is, when the molded body before firing of the ceramic separator 18 is manufactured by die molding, the terminal receiving hole 72 and the insertion hole 18a are often formed by separate mandrels. At this time, the mandrel mating surfaces are positioned on the bottom surface outer edge 18e1 of the separator 18, and powder may be pressed into the gaps between the mating surfaces to generate burrs in the molded body. Therefore, if the bottom edge 18e1 of the separator 18 is chamfered, even if burrs are generated, it is difficult to cause a problem that the fragments and the like adhere to the separator bottom surface 18e to form unnecessary protrusions. Can do.

  Further, a convex portion 18f1 protruding into the heating element side lead wire insertion hole 18a2 is formed in the central skeleton portion 18f so as to be orthogonal to the central axis O2, thereby forming a gap forming portion S. If the heater terminal 3b is supported by the convex portion 18f1 and is inserted into the heating element side lead wire insertion hole 18a2 while being separated from the bottom surface outer edge 18e1, the expanded portion 3b2 of the heater terminal 3b is gradually expanded by elastic deformation. The heater terminal 3b is smoothly inserted.

  FIG. 10 shows a third embodiment of the assembled state of the ceramic separator 18 and the heating element 3. In this embodiment, projecting surfaces F1 and F1 projecting in a spherical shape toward the mating side are formed on the heating element end surface 3c and the separator bottom surface 18e, respectively. A point contact state can be more easily obtained at the tips of the projecting surfaces F1 and F1, and the occurrence of chipping, cracks, and the like can be suppressed.

  In FIG. 10, a partition wall 100 is formed between the heating element side lead wire insertion hole 18 a 2 and the heater terminal accommodating portion 72 d and the central communication portion 72 e, and a radial communication hole 101 is opened in the partition wall 100. The heating element side lead wire insertion hole 18a2 and the central communication portion 72e are communicated with each other. The heater terminal 3b is formed with a widened portion 3b2 that expands in a tapered shape (for example, a U-shape) radially outward with respect to the bottom surface outer edge 18e1 of the separator 18 to form a gap forming portion S. In this case, the expanded portion 3b2 of the heater terminal 3b may be plastically deformed before the insertion process into the heater terminal accommodating portion 72d and the heating element side lead wire insertion hole 18a2.

  Next, a modification of the first embodiment shown in FIG. 8 is shown in FIG. Among these, FIG. 11A shows an example in which chamfers 18e2 and 3c2 are formed in order to prevent chipping, cracks, and the like at the separator bottom surface 18e and the outer edges 18e1 and 3c1 of the heating element end surface 3c. In (b), the separator bottom surface 18e is formed with a projecting surface F1 (curvature radius R1) projecting in a spherical shape toward the heating element end surface 3c, and the heating element end surface 3c has a spherical shape corresponding to the projecting surface F1. The concave surface F2 (curvature radius R2 ≧ R1) is formed. In this case, it is preferable to chamfer 3c2 (see the detailed example 1) or form a spherical surface with a radius r (see the detailed example 2) on the outer peripheral portion of the heating element end face 3c.

  Further, a modification of the second embodiment shown in FIG. 9 is shown in FIG. Among these, in Fig.12 (a), while the protrusion surface F1 which protrudes in spherical shape toward the separator bottom face 18e side is formed in the heat generating body end surface 3c, the separator bottom face 18e is formed in planar shape. In (b), as the gap forming portion S, an elastic support portion 3b3 is formed on the heater terminal 3b instead of forming the convex portion 18f1 on the central skeleton portion 18f of FIG. This elastic support portion 3b3 is formed in the heater terminal 3b, extends from one end located on the rear side in the center axis O2 direction to the front side, and passes through the direction change portion and reaches the other end on the rear side inside the cut 3b4. The tongue piece 3b5 is positioned at the rear side, and is formed by causing the tongue 3b5 in the insertion direction of the heating element 3 with the support shaft 3b6 as a fulcrum. The elastic support portion 3b3 prevents the heater terminal 3b from jumping out from the heating element side lead wire insertion hole 18a2.

  In FIGS. 11 and 12, the same reference numerals are given to portions common to the corresponding diagrams (FIG. 8 or FIG. 9), and description thereof is omitted. In FIG. 12B, the enlarged view of the portion X2 is the same as FIG.

The longitudinal cross-sectional view showing one Example of the oxygen sensor which concerns on this invention. FIG. 2 is a partially enlarged longitudinal sectional view of the oxygen sensor of FIG. 1. The disassembled perspective view which shows the assembly | attachment state to a ceramic separator. The longitudinal cross-sectional view which shows the assembly | attachment state of the heat generating body to an oxygen detection element. The top view and front half sectional view of an outer cylinder. The top view of a ceramic separator, a bottom view, and AA and BB sectional drawing. The disassembled perspective view which shows the assembly | attachment state of a grommet and a ventilation part. The longitudinal cross-sectional view of the 1st Example which shows the assembly | attachment state of a ceramic separator and a heat generating body. The longitudinal cross-sectional view of the 2nd Example which shows the assembly | attachment state of a ceramic separator and a heat generating body. The longitudinal cross-sectional view of the 3rd Example which shows the assembly | attachment state of a ceramic separator and a heat generating body. The longitudinal cross-sectional view which shows the example of a change of FIG. The longitudinal cross-sectional view which shows the example of a change of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Oxygen sensor 2 Oxygen detection element 2a Hollow part 3 Heat generating body 3a Heat generating part 3b Heater terminal 3b1 Base end part 3b2 Expanded part 3b3 Elastic support part 3b4 Cut 3b5 Tongue piece 3b6 Raising support shaft 3c Rear end face (heat generating element end face)
3c1 Outer edge 3c2 Chamfer 9 Metal shell 16 Outer cylinder 17 Grommet 17a1 Detection element side lead wire insertion hole 17a2 Heating element side lead wire insertion hole 18 Ceramic separator (separator)
18a1 Detection element side lead wire insertion hole 18a2 Heating element side lead wire insertion hole (lead wire insertion hole)
18e Bottom (Separator bottom)
18e1 outer edge (bottom edge)
18e2 Chamfer (Chamfer)
18f Central skeleton part 18f1 Convex part 20, 21 Detection element side lead wire 19, 22 Heating element side lead wire (lead wire)
23 First terminal fitting (pressing member)
72 Terminal receiving hole 72e Central communication part (heating element end receiving hole)
F1 Projection surface F2 Concave surface S Gap forming portion O1 Heater center axis O2 Separator center axis R1 Curvature radius of projection surface F1 R2 Curvature radius of recess surface F2

Claims (9)

The front end portion has a closed hollow shaft shape, and the front end portion side is directed to the gas to be measured, and an oxygen detection element,
An axial heating element that is disposed in a hollow portion of the oxygen detection element and heats the oxygen detection element;
A separator having a heating element end accommodating hole that is disposed substantially coaxially with the hollow portion on the rear side of the oxygen detection element, has a front end surface opened, and a rear end portion of the heating element is inserted;
The heating element end accommodating hole has a bottom surface at an intermediate position in the axial direction of the separator, and a heater terminal extended from the rear end side of the heating element inserted into the heating element end accommodating hole, A lead wire insertion hole allowing insertion of a connected lead wire is communicated with the heating element end accommodating hole in the circumferential direction,
In addition, in order to prevent the heater terminal inserted through the lead wire insertion hole and the outer edge of the bottom surface of the heating element end accommodating hole (hereinafter referred to as the bottom surface outer edge) from contacting or interfering with each other, The oxygen sensor is characterized in that a gap forming portion for forming a certain amount of gap between the heater terminal and the outer edge of the bottom surface is formed in the heater terminal and / or the separator in a direction orthogonal to the heater terminal.   The lead wire insertion hole penetrates the separator in the axial direction, and the front end side in the axial direction communicates with the heating element end receiving hole at the outer edge of the bottom surface, and is integrated with the heating element end receiving hole. The oxygen sensor according to claim 1.   The gap forming portion is formed on the heater terminal having a base end portion fixed to the rear end side of the heating element, and expands continuously or stepwise radially outward with respect to the bottom edge. The oxygen sensor according to claim 1 or 2.   The oxygen sensor according to claim 1, wherein the gap forming portion is a chamfered portion that is provided on an outer edge of the bottom surface of the separator and has a predetermined inclination with respect to the axis.   In the central skeleton portion of the separator surrounded by the bottom surface of the heating element end portion receiving hole and the lead wire insertion hole, the gap forming portion extends from the central skeleton portion to the lead wire in a direction intersecting the axis. The oxygen sensor according to claim 1, wherein the oxygen sensor is a protrusion protruding into the insertion hole.   The gap forming portion is formed on the heater terminal, and extends in a predetermined direction from one end, and a tongue piece located inside a cut extending from the one end to the other end in the insertion direction of the heating element. The oxygen sensor according to claim 1 or 2, wherein the oxygen sensor is an elastic support portion in a form to cause.   The oxygen sensor according to claim 6, wherein the elastic support portion is formed by causing a support shaft to be located rearward in the axial direction and causing the tongue piece located on the front side of the cause support shaft.   The bottom surface (hereinafter referred to as a separator bottom surface) of the heating element end portion accommodation hole formed in the separator and a rear end surface (hereinafter referred to as a heating element end surface) of the heating element are arranged to face each other, and the separator bottom surface The oxygen sensor according to any one of claims 1 to 7, wherein at least one of the end faces of the heat generating body has a projecting surface that projects in a form in which the tip side continuously reduces in cross section in the facing direction.   The oxygen sensor according to claim 8, wherein the bottom surface of the separator and the end surface of the heating element are in contact with each other in a point-like contact state at a tip of the protruding surface.

Images