JP2002039986A - Oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen sensor, capable of obtaining high reliability and long product life by preventing the occurrence of chippings, cracks, etc., in the outer edge of the bottom surface of a separator in assembly and avoiding the states of operational failures and inoperatable. SOLUTION: A housing hole 72e for the end of a heating element comprises a bottom surface 18e, and a through-hole 18a2 for a lead wire is connected to the housing-hole 72e in the circumferential direction. A gap forming part S to form a predetermined amount of gap between a heater terminal 3b and the outer edge 18e1 of the bottom surface of the separator, in the direction which intersects the axis O2 of the separator 18 at right angles is formed in the heater terminal and/or the separator. By forming the gap-forming part in at least one of both, it is possible to prevent the contact and interference between the heater terminal and the outer edge of the bottom surface, when the rear end of the heating element 3 is inserted into and assembled to the housing hole 72e for the end part of the heating element. When there is no need for narrowing the area of the bottom surface of the separator and thinning the center skeleton part 18f of the separator, the strength of the separator will not be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor for detecting oxygen in a gas to be measured, for example, an exhaust gas of an internal combustion engine.

[0002]

2. Description of the Related Art As one form of such an oxygen sensor,
It is known that the front end has a closed hollow shaft shape, and the front end is provided with an oxygen detection element directed to a gas to be measured. 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 exhaust gas to be measured contacts the outer surface of the oxygen detection element. Oxygen concentration cell electromotive force is generated according to the oxygen concentration difference between the inner and outer surfaces. And
The oxygen concentration in the exhaust gas can be detected by extracting the electromotive force of the oxygen concentration cell as a detection signal of the oxygen concentration in the exhaust gas from the inner and outer surfaces via a lead wire or the like.

[0003]

In an oxygen sensor of this type, when the exhaust gas temperature is low, for example, immediately after the start of the engine, the activity of the oxygen detection element constituted by the solid electrolyte member is not sufficient, and the electromotive force that can be measured is low. It takes a considerable amount of time before you can take out. Therefore, by inserting a shaft-shaped heating element with a heating part into the hollow part of the oxygen detection element, and heating and activating the oxygen detection element at the time of engine start, measurement can be quickly performed at the time of start, where harmful components are generated relatively frequently. The output (electromotive force) is raised.

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

On the other hand, in order to facilitate positioning of the heating element at the time of assembly and shorten the overall length of the oxygen sensor, a separator disposed behind the oxygen detecting element is provided with a heating element end receiving hole having an open front end face. Formed, and the rear end face of the heating element (hereinafter, referred to as
In some cases, the heating element end face is brought into contact with the bottom surface of the heating element end receiving hole (hereinafter, referred to as a separator bottom face).
At this time, as described above, if the center axis of the heating element is inclined with respect to the center axis of the oxygen detection element or is eccentric so as to be shifted to one side, the heating element after the heating element to the end receiving hole of the heating element ends. When the ends are inserted and assembled, the heater terminals extending from the rear end side of the heating element easily come into contact with and interfere with the outer edge of the bottom surface of the separator (hereinafter, referred to as the bottom edge). Due to the contact and interference, chipping (cracking), cracking (crack), and the like are generated at the outer edge of the bottom surface, and there is a possibility that the oxygen sensor (oxygen detecting element) may malfunction or become inoperable due to these dropped fragments. Even if the heating element and the separator are not eccentric in design, a similar situation may occur due to a manufacturing error, an uneven pushing force at the time of assembly, and the like.

Therefore, by making the bottom surface of the separator narrow (that is, to keep the area of the bottom surface of the separator small), it is possible to avoid contact and interference of the heater terminal with the outer edge of the bottom surface. However, this reduces the thickness of the central skeleton including the central axis of the separator and the bottom surface of the separator, and thus the strength of the separator may be insufficient. For example, when the bottom surface of the separator comes into contact with the end surface of the heating element and is repeatedly subjected to vibration or the like during operation of the internal combustion engine, fatigue fracture 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 chipping, cracks, and the like from occurring at the outer edge of the bottom surface of the separator during assembling while sufficiently securing the strength of the separator, and to avoid malfunction and inoperability. An object of the present invention is to provide an oxygen sensor that can achieve high reliability and product life.

[0008]

In order to solve the above problems, the oxygen sensor of the present invention has a hollow shaft shape with a closed front end, and the front end is directed toward the gas to be measured. The oxygen detecting element is disposed in a hollow portion of the oxygen detecting element, and an axial heating element for heating the oxygen detecting element is disposed substantially coaxially with the hollow portion on the rear side of the oxygen detecting element. A separator having a heating element end accommodating hole into which a front end face is opened and a rear end of the heating element is inserted, wherein the heating element end accommodating hole has a bottom surface at an intermediate position in the axial direction of the separator. A heater terminal extending from the rear end side of the heating element inserted into the heating element end accommodating hole and a lead wire insertion hole through which a lead wire connected to the heater terminal can be inserted have a circumferential direction. The heating element end receiving hole In order to prevent the heater terminal being communicated with and being inserted into the lead wire insertion hole, and the outer edge of the bottom surface from contacting and interfering with each other, the heater terminal and the bottom surface are arranged in a direction orthogonal to the axis. A gap forming part that forms a certain amount of gap between the outer edge and the outer edge is formed in the heater terminal and / or the separator.

According to the present invention, the heating element end receiving hole has a bottom surface, the lead wire insertion hole is communicated with the heating element end receiving hole in the circumferential direction, and is perpendicular to the axis of the separator. In the orientation, a gap forming portion that forms a certain amount of gap between the heater terminal and the outer edge of the bottom surface of the separator is formed in the heater terminal and / or the separator. A gap is formed in at least one of the heater terminal and the separator to prevent contact and interference between the heater terminal and the bottom edge when the rear end of the heating element is inserted into the heating element end receiving hole and assembled. can do. Therefore, chipping and cracking are less likely to occur at the outer edge of the bottom surface of the separator, and it is possible to prevent the oxygen sensor (oxygen detection element) from malfunctioning or becoming inoperable due to these falling debris. And product life can be increased. As described above, 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 center axis of the heating element is arranged to be inclined with respect to the center axis of the oxygen detection element. This is particularly effective when eccentrically arranged so as to be shifted 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, it is not necessary to reduce the area of the bottom surface of the separator and to make the central skeleton portion of the separator thin. Is not reduced. Therefore, even in a state where the bottom surface of the separator is in contact with the end surface of the heating element and is repeatedly subjected to vibration or the like during operation of the internal combustion engine, fatigue fracture or the like is unlikely to occur in the central skeleton portion of the separator for a long time.

[0011] Here, the lead wire insertion hole penetrates the separator in the axial direction, and the front end in the axial direction communicates with the end receiving hole of the heating element at the outer edge of the bottom surface to be integrated with the end receiving hole of the heating element. In this case, 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 thus, the contact and interference between the heater terminal and the bottom edge are further reduced. .

The gap forming portion is formed in a heater terminal having a base end fixed to the rear end side of the heating element, and is continuously or stepwise expanded radially outward with respect to an outer edge of the bottom surface. It can be an opening. With this arrangement, the arrangement of the heating element end receiving hole and the lead wire insertion hole is matched with the shape of the heater terminal, and the heater terminal that expands radially outward does not contact or interfere with the outer edge of the bottom surface of the separator. It can be smoothly inserted from the end of the heating element into the lead wire insertion hole. When no gap forming portion is formed on the separator side, it is desirable that the expanded portion of the heater terminal be plastically deformed in advance before insertion into the lead wire insertion hole.

[0013] The gap forming portion may be a chamfered portion formed on the outer edge of the bottom surface of the separator and having a predetermined inclination with respect to the axis thereof. Since the outer edge of the bottom surface of the separator is formed to have a small diameter by an amount corresponding to the formation of the chamfered portion, the heater terminals are 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 where chipping, cracks, and the like are likely to occur and easily fall off, the generation of these and the scattering of the fallen fragments can be effectively prevented. Further, there is an advantage in the following manufacturing process. That is, when the molded body of the separator is manufactured by die molding, the burr due to the position of the mating surface of the mandrel forming the heating element end accommodating hole and the mandrel forming the lead wire insertion hole is located at the outer edge of the bottom surface of the separator. Can be prevented by chamfering the outer edge of the bottom surface.

Next, the gap forming portion is moved from the central skeleton portion to the central skeleton portion of the separator, which is surrounded by the bottom surface of the heating element end receiving hole and the lead wire insertion hole, in a direction intersecting the axis. It may be a projection projecting into the insertion hole. While the heater terminal is supported by the convex portion, the heater terminal can be smoothly inserted into the lead wire insertion hole while being separated from the outer edge of the bottom surface, and at this time, the convex portion is inserted along with the insertion of the heater terminal into the lead wire insertion hole. And a jig for gradually expanding the heater terminals. In this case, it is desirable that the heater terminal be elastically deformed by being inserted into the lead wire insertion hole.

Further, a tongue piece formed in the heater terminal, extending in a predetermined direction from one end, and located inside a cut reaching the other end through the direction changing portion,
The elastic supporting portion can be configured to be caused in the insertion direction of the heating element. Since the heater terminal is securely held in the lead wire insertion hole by the elastic support portion, a short circuit or disconnection caused by the heater terminal jumping out of the lead wire insertion hole due to a pushing force at the time of assembly or vibration during operation of the internal combustion engine or the like. 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 rearward in the axial direction of the separator, and the tongue piece positioned forward of the support shaft is raised. It is desirable to form it. The heater terminals other than the elastic support portions may be plastically deformed before insertion into the lead wire insertion holes, or may be elastically deformed by insertion into the lead wire insertion holes.

The bottom surface of the separator and the end surface of the heating element are arranged opposite to each other, and at least one of the bottom surface of the separator and the end surface of the heating element projects in such a manner that the leading end side continuously decreases in cross section in the facing direction. In some cases. The projecting surfaces are opposed to each other, and can prevent chipping, cracks, and the like from being generated on the separator bottom surface and the heating element end surface, which are surfaces that can be brought into contact by a pushing force at the time of assembly or vibration during operation of the internal combustion engine. .

In the case where the bottom face of the separator and the end face of the heating element which are opposed to each other come into contact with each other, it is desirable that the tip end of the protruding face comes into contact in a point-like contact state. The occurrence of chipping, cracks, and the like on the bottom surface and the end surface of the heating element can be suppressed. Moreover, as described above, by forming the gap forming portion,
Since the strength of the separator is sufficiently ensured, even if the bottom surface of the separator comes into contact with the end surface of the heating element and is repeatedly subjected to vibrations during operation of the internal combustion engine, fatigue fracture or the like is unlikely to occur in the central skeleton portion of the separator for a long time. In this specification, the point-like contact state refers to a point contact or a state similar thereto.

[0018]

Embodiments of the present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 shows the internal structure of an embodiment of the 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 having a closed end, and a heating element 3 inserted into a 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. In addition, as such a solid electrolyte, Y ₂
Although ZrO ₂ in which O ₃ or CaO is dissolved is typical, a solid solution of an oxide of another alkaline earth metal or rare earth metal and ZrO ₂ may be used. Further, HfO ₂ may be contained in ZrO _{2 serving as} a base. As shown in FIGS. 2 and 3, an internal electrode layer 2 c made of, for example, Pt or a Pt alloy is formed on the inner surface of the hollow portion 2 a of the oxygen detection element 2 so as to cover almost the entire surface. On the other hand, external electrode layers 2b are similarly provided on the outer surfaces thereof so as to cover the front portions thereof. Further, a cylindrical metal casing 10 is provided outside the intermediate portion of the oxygen detection element 2 via insulators 6 and 7 formed of insulating ceramics and ceramic powder 8 formed of talc.
In the following description, the side (closed side) toward the axial end 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 screw portion 9b for mounting the oxygen sensor 1 to a mounting portion such as an exhaust pipe, and a protector 11 mounted so as to cover a front opening of the metal shell 9. Become. The oxygen sensor 1 of this embodiment is used in a position such that the front of the screw portion 9b is located in the engine such as an exhaust pipe, and the rear is located in the outside atmosphere. The metal shell 9 (casing 10) holds the oxygen detection element 2 in a state where the front end side (detection section) of the oxygen detection element 2 protrudes from its front opening so as to be directed to the exhaust gas to be measured. At the same time, a cap-shaped protector 11 is mounted on a cylindrical protector mounting portion 9a formed in the opening, and covers the detection portion of the oxygen detection element 2 with a predetermined space therebetween. In the protector 11,
A plurality of gas permeation ports 12 for transmitting exhaust gas are formed in a penetrating form.

The rear portion of the metal shell 9 is caulked with the insulator 6 via a ring 15, and the metal shell 9 has an opening 16 F formed at the front end of a cylindrical metal outer cylinder 16. 6 (see FIG. 6). Then, the entire circumference laser welded portion 16 formed along the circumferential direction of the metal shell 9.
E is the inner peripheral surface of the front end opening 16F of the outer cylinder 16 and the metal shell 9
Is joined and fixed to the outer peripheral surface. Also, this outer cylinder 16
The rear end opening 16R is a grommet 1 made of rubber or the like.
7 is fitted therein, and a ceramic separator 18 (hereinafter, also simply referred to as a separator) is provided on the front side subsequently. The detection element-side lead wires 20, 21 and the heating element-side lead wires 19, 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 covers the ceramic separator 18 from the outside, and its front end opening 16F is
0 is substantially coaxially overlapped and connected from the rear outside from outside. The grommet 17 is located on the rear side of the ceramic separator 18 and is elastically fitted inside the rear end opening 16 </ b> R of the outer cylinder 16.

Next, one of the detection element-side lead wires 20, 21 has a connector 23a, a lead wire portion 23b, a fixing portion 23c, and a downward pressing portion 23d integrally formed with each other. Terminal fitting 23 (pressing member)
The internal electrode layer 2c of the oxygen detection element 2 described above (FIG. 2)
Is electrically connected to Also, the other lead wire 20
Passes through a second terminal fitting 33 having a connector 33a, a lead wire 33b, and a fitting body 33c formed integrally with each other, and passes through the external electrode layer 2b of the oxygen detecting element 2 (FIG. 3).
Is electrically connected to The oxygen detecting element 2 is activated by being heated by the heating element 3 arranged inside. The heating element 3 is a rod-shaped ceramic heater, and Al ₂
Heating portions 3a having a resistance heating element (not shown) in a core material mainly composed of O ₃ are provided with heater terminals 3b, 3 on the + and − pole sides.
Electricity is supplied through the heating element side lead wires 19 and 22 (FIG. 7) connected to b, thereby heating the tip (detection section) of the oxygen detection element 2. Sensing element side lead wires 20, 21
The heating element-side lead wires 19 and 22 are provided in the form of two detection element-side lead wire insertion holes 18a1 and 18a1 and heating element-side lead wire insertion holes 18a2 and 18a2 (lead wires), which are provided through the ceramic separator 18 in the axial direction. Insertion holes) and two detection element side lead wire insertion holes 17 a 1, 17 provided through the grommet 17 in the axial direction.
a1 and the heating element side lead wire insertion holes 17a2 and 17a2, respectively, and are 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 of the heating element 3 is pressed. 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 lower pressing portion 23d is fitted into the inner surface of the oxygen detection element 2 to fix 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 circumferential position of the fixed portion 23c, and a connector 23a is further integrated at the other end. In the upper part (rear part) of the fixing part 23c, a U-shaped cut is formed in a part of the peripheral surface of the fixing part 23c near the left and right edges of the opening provided in the fixing part 23c. Are folded radially inward to form a pair of left and right upper pressing portions 23e. 23g is a flange for preventing the fixing portion 23c from entering the heat-generating-element end-portion accommodation hole 18c.

On the other hand, the second terminal fitting 33 has a cylindrical fitting main body 33c, and is integrated with one end of a lead wire portion 33b connected to one circumferential position of the fitting main body 33c. At the other end, a connector 33a is integrated. On the other hand, the lead wire portion 3 sandwiching the center axis line
On the side opposite to the connection point 3b, an axial slit 33e
Are formed. The rear end of the oxygen detecting element 2 is inserted into the inside of the metal fitting body 33c from the inside in such a manner as to elastically push the oxygen detecting element 2 apart. Specifically, a conductive layer 2f 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 2s of the oxygen detection element 2 by, for example, electroless plating. On the other hand, the conductive layer 2f is formed by pattern formation and baking using, for example, a metal paste, and is electrically connected to the external electrode layer 2b via a similarly formed axial connection pattern layer 2h. I have.

As shown in FIG. 4, the heating element 3 is pressed by the lower pressing portion 23d and the upper pressing portion 23e in a direction intersecting with the central axis O2 of the hollow portion 2a of the oxygen detecting element 2, and the central axis of the heating element 3 is O1 is arranged eccentrically (offset) so as to be shifted to one side with respect to the center axis O2 of the hollow portion 2a of the oxygen detection element 2, and at least a part of the heating element 3 is located inside the hollow portion 2a of the oxygen detection element 2. Contacting the wall.

FIG. 5 shows the outer cylinder 16. The outer cylinder 16 is divided into two parts in the front and rear direction in the axial direction, and an outer cylinder-side support part 16 formed at the rear of a front outer cylinder member 161 located on the front side.
A front portion of the rear outer cylinder member 162 on the rear side is substantially coaxially overlapped and connected from the rear outer side. In this overlapping connection portion, the entire circumference 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 formed as a connecting portion. It is formed along the circumferential direction. The front end opening 16F of the outer cylinder 16 is substantially coaxially overlapped and connected to the metal shell 9 from the rear outside, and 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 are connected. The entire circumference laser welded portion 16E to be joined is formed along the circumferential direction of the metal shell 9.

Next, the outer cylinder side support portion 16A formed at the rear of the front outer cylinder member 161 will be described with reference to FIG. The outer cylinder-side support portion 16A has a tapered shape in which the outer diameter becomes smaller toward the rear side as a whole, and such a shape is realized by the following configuration. The outer cylinder-side support portion 16A is formed with two reduced diameter portions having a configuration in which the outer diameter decreases in an inclined manner toward the rear side in the axial direction. Of the two reduced diameter portions, a front side cylinder is provided between the first reduced diameter portion 16a1 formed on the front side and the second reduced diameter portion 16a2 formed on the rear side in a form substantially parallel to the axis. A shape 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 above-described full-circumference laser welded portion 16C is formed along the circumferential direction of the connecting portion. Have been.

A second cylindrical portion 16b2 is formed on the rear side of the second reduced diameter portion 16a2 so as to be substantially along the outer peripheral surface of the main body 18B of the separator 18.
Further, the rear side of the second cylindrical portion 16b2 is bent radially inward to form a bent portion 16c.
The rear-side support surface 16c1 of the separator 6c is
A has a form in contact with the front support surface 18A1 of A. When the main body 18B of the separator 18 is disposed inside the outer cylinder-side support 16A, the bent portion 16c formed in this manner serves as a receiving member for the front-side support surface 18A1 of the separator-side support 18A. Function. The rear support surface 16c1 of the bent portion 16c is bent radially inward, and serves as a guide when the main body portion 18B of the separator 18 is inserted into the outer cylinder side support portion 16A. I have.

As described above, the outer cylinder side support portion 16A is composed of 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 forms the outer peripheral surface of the main body portion 18B of the separator 18 with a space formed therebetween. It is provided so as to enclose and surround the part S3 (see FIG. 2). Therefore, the impact force exerted on the outer cylinder 16 by a stepping stone or the like is reduced by the two reduced diameter portions 16a.
Attenuated by the spring effect of the first and 16a2 and the isolation effect of the space S3 and transmitted to the separator 18, breakage of the separator 18 can be prevented.

On the other hand, the rear outer cylindrical member 162 has the grommet 17 inserted into the inside of the rear end opening 16R. On the front side of the grommet 17 insertion portion, the inner diameter is inclined toward the front (continuously). (2) An enlarged diameter portion 16B having a larger form is provided. The inner peripheral surface of the rear end opening 16R of the rear outer cylinder member 162 is used as an insertion guide for the outer peripheral surface of the separator-side support portion 18A.

The thickness of the front outer cylinder member 161 provided on the front side is determined in consideration of the impact resistance against a stepping stone and the amount of heat transfer to the grommet side (rear side).
1 is the thickness t2 of the rear outer cylinder member 162 provided on the rear side.
That's it. In other words, the front outer cylinder member 161 on the front side (detection element side), which is likely to be in a low position during attachment and has a high probability of hitting a hopping stone, 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 mounting position of the grommet 17 has a relatively thin thickness 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 or less).
mm), and the thickness t2 of the rear side outer cylinder member 162 is desirably 0.3 mm or more and 0.5 mm or less (for example, 0.3 mm).

In FIG. 2, the separator-side support portion 18A
Between the outer peripheral surface of the outer cylindrical member and the inner peripheral surface of the rear outer cylinder member 162.
An annular gap S0 having a radial interval of, for example, 0.3 mm or more is provided. The gap S0 is determined by a stepping stone or the like.
Is applied to the separator 1 directly from the outer cylinder 16.
8 to form an annular space. 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 the details of the ceramic separator 18. The main body 18B of the ceramic separator 18 whose cross section perpendicular to the axis is formed in a circular shape has a lead wire 2 on the detecting element side.
0, 21 and the heating element side lead wires 19, 22 (see FIG. 7)
And the heating element-side lead wire insertion holes 18a1 and 18a1 and the heating element-side lead wire insertion holes 18a
2, 18a2 (hereinafter, collectively referred to as insertion holes 18
a) is formed penetrating 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 circular cross-section orthogonal to the axis is formed in a form projecting outwardly and integrally 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. Ceramic separator 18 (separator side support 18A)
At the rear end face, the ventilation groove 18b has four insertion holes 18a.
Are formed in a direction not perpendicular to the axis in a cross shape at a position that does not interfere with the axis. The ventilation groove 18b is formed between the detection element side lead wire insertion holes 18a1 and 18a1 and the detection element side lead wires 20 and 2.
1 (see FIG. 2).

The ceramic separator 18 has four insertion holes 1 from the rear end (the upper end in FIGS. 6C and 6D).
8a penetrate in the axial direction at approximately 90 ° intervals along a pitch circle P centered on the central axis O2. Further, a terminal receiving 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 substantially at the center of the entire length along the axial direction. The terminal receiving hole 72 has a first receiving portion 72b, a second receiving portion 72c, two heater terminal receiving portions 72d, 72d, and a central communication portion 72e (a heating element end receiving hole).
The first housing part 72b and the second housing part 72c insert and hold the first connection fitting 23 and the second connection fitting 33 from the front side to the rear side, respectively.
72d inserts and holds the heater terminals 3b, 3b on the positive and negative pole sides from the front side to the rear side, respectively. And the central communication part 72e is provided with these four accommodation parts 72b,
It is located in the middle of 72c, 72d, and 72d, and is formed in a communication form with each of the receiving portions. Specifically, the first and second housing portions 72b and 72c and the two heater terminal housing portions 72d and 72d are in a state of facing each other with the central communication portion 72e interposed therebetween, and are arranged at intervals of approximately 90 ° along the pitch circle P. It has the same positional relationship as the insertion hole 18a.

The first housing portion 72b, the second housing portion 72c, and the two heater terminal housing portions 72d, 72d each have a narrow opening facing the central communication portion 72e and a central communication portion 7c.
2e, a wide bottom extending in the outer peripheral direction (depth direction) on the opposite side, and the opening width (distance between walls) from opening to bottom.
6 is gradually widened, and is formed as a space surrounded by a partition wall 18c including an inclined portion connecting both of them (FIG. 6).
(B)). Each of the storage sections 72b, 72c, 72d,
72d has a shell-like shape partially open 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 main body 33c of the second connecting metal fitting 33 is formed at the opening end face (front end face) of the terminal receiving hole 72 of the ceramic separator 18 by a partition wall. 18c is in contact with the front end face. On the other hand, the rear edge of the metal fitting body 23c of the first connecting metal 23 is
The second connection fitting 33 is in contact with the front end face of the partition wall 18c inside the fitting body 33c and the pitch circle P. A partition 18c formed between adjacent insertion holes 18a
Are formed to protrude inward from the pitch circle P, respectively. The inner diameter of the central communication portion 72e is the heating element 3
The rear end face 3c (heating element end face) of the heating element 3 extends from the front end side of the terminal receiving hole 72 along the axial center to the bottom surface 18e ( (The bottom of the separator). This facilitates positioning of the heating element 3 in the axial direction at the time of assembly, shortens the overall length of the oxygen sensor 1, and realizes downsizing of the sensor size.

The front half of the ceramic separator 18 is viewed from the front end (FIG. 6).
(B)) The four insertion holes 18a overlap (include) the terminal receiving holes 72 inside the pitch circle P.
In form, they are integrated. Specifically, the insertion hole 18a
Of the bottom surface 18e is the outer edge 18e1 of the bottom surface 18e.
At the center communication portion (heating element end accommodating hole) 72e, and is overlapped with and integrated with the central communication portion 72e. On the other hand, the rear half of the ceramic separator 18 includes the central axis O2 and has four insertion holes 18a.
And a bottom frame 18e, a central skeleton portion 18f that stands up in a columnar shape (for example, a columnar shape, a polygonal columnar shape, or the like) is formed. That is, the bottom surface 18e forms the distal end surface of the central skeleton portion 18f.

FIG. 7 shows an assembled state of the grommet 17 and the ventilation part 53. The grommet 17 has two detection element-side lead insertion holes 17a for inserting the detection element-side leads 20, 21 and the heating element-side leads 19, 22.
1, 17a1 and heating element side lead wire insertion holes 17a2, 1
7a2 (hereinafter referred to as an insertion hole 17a when these are collectively referred to) is provided through the inside thereof in the axial direction.
A center through hole 17b is provided at a radially central portion of the grommet 17, and a ventilation portion 53 is fitted into the center 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 surfaces of the ventilation portion 53 and the lead wires 19, 20, 21, 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 penetrate and the waterproof property is enhanced.

The ventilation section 53 is composed of a filter 53A and a filter support 53B. Filter 53A
Has a cylindrical peripheral surface portion 53A1 extending in the axial direction, and a ventilation end surface portion 53A2 which is connected to the peripheral surface portion 53A1 in a lid shape at a rear end and guides outside air in the axial direction. And has an inverted U-shape. And the cylindrical filter support bracket 53B has a flange 53B2 at the front end,
The cylindrical peripheral surface portion 53B1 extending in the axial direction is
A, the filter 5 is fitted into the cylindrical peripheral surface 53A1.
3A is supported from the inside, and when the small diameter portion 16c of the outer cylinder 16 is swaged to form the grommet swaged portion 16B, the cylindrical peripheral surface 53A1 of the filter 53A is supported so as not to be broken. Grommet 17
, 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 of the oxygen sensor 1 that is exposed to the highest temperature, which is advantageous for the heat resistance of the filter 53A.

Filter 53A or filter support bracket 53
B can be provided with an inclined surface such as a taper along the axial direction on the inner and outer peripheral surfaces so that the fitting can be firm. The filter 53A can be rotated by 180 ° from the state shown in FIG. 7 to position the ventilation end face 53A2 at the bottom (front end). However, in order to prevent the intrusion of water or the like, the rear end face of the grommet 17 and the ventilation end face are prevented. The state of FIG. 7 in which the portion 53A2 and the portion 53A2 are substantially flush is more desirable. Note that the filter 53A is
For example, with a porous fiber structure of polytetrafluoroethylene (PTFE) (trade name: for example, Gore-Tex (Japan Gore-Tex Co., Ltd.)), permeation of a liquid mainly containing water such as water droplets is prevented, and air And / or is configured as a water-repellent filter that allows gas permeation, such as water vapor.

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

FIG. 8 is a longitudinal sectional view of the first embodiment showing an 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 to face each other in the central communication portion 72e, and a projection face F1 that projects spherically toward the flat heating element end face 3c is formed on the separator bottom face 18e. Have been. As a result, at the tip of the protruding surface F1, the separator bottom surface 18e and the heating element end surface 3c abut in a point-like contact state, and the contact area is reduced, so that chipping, cracks, etc. are less likely to occur on these surfaces. .

The heater terminal 3b has an intermediate portion following the base end portion 3b1 fixed to the rear end side of the heating element 3, and a separator 18a.
Of the bottom surface 18e1 in a stepped shape (for example, an L-shaped crank shape) radially outward to form an expanded portion 3b2. The expanded portion 3b2 forms a predetermined gap between the heater terminal 3b and the bottom outer edge 18e1 in a direction orthogonal to the central axis O2 of the separator 18. This gap prevents the heater terminal 3b from contacting and interfering with the bottom outer edge 18e1.
d and the heating element side lead wire insertion holes 18a2 are smoothly inserted into the opening portions 3b2, so that the expanding portions 3b2 have a function as gap forming portions S. In addition, the expanded portion 3 of this heater terminal 3b
If b2 is plastically deformed by bending or the like before the insertion step, the assembling operation can be performed efficiently.

FIG. 9 shows a second embodiment of the assembled state of the ceramic separator 18 and the heating element 3. In this embodiment, a protruding surface F1 protruding spherically toward the separator bottom surface 18e is formed on the end surface 3c of the heating element.
A spherical concave surface F2 corresponding to the protruding surface F1 is formed on the separator bottom surface 18e. And, the radius of curvature R2 of the concave surface F2 formed on the separator bottom surface 18e is made larger than the radius of curvature R1 of the protruding surface F1 formed on the heating element end surface 3c, thereby having a pivot bearing configuration. Thus, the heating element end face 3c and the separator bottom face 18e can be smoothly rotated relative to each other, and the occurrence of twisting between the heating element 3 and the separator 18 is reduced.

An outer edge 18e1 of the separator bottom surface 18e has a chamfer 1 having a predetermined inclination with respect to the central axis O2.
8e2 is applied to form the gap forming portion S. Contact and interference between the heater terminal 3b and the bottom outer edge 18e1 can be prevented, and the occurrence of chipping, cracks, and the like, and the scattering of falling pieces can be prevented. Further, there is an advantage in the following manufacturing process. That is, the ceramic separator 1
In the case where the molded body 8 before firing is manufactured by die molding, the terminal accommodating hole 72 and the insertion hole 18a are often formed by separate mandrels. At this time, the mating surfaces of these mandrels are located at the outer peripheral edge 18e1 of the bottom surface of the separator 18, and powder may be pressed into gaps between the mating surfaces to generate burrs on the molded body. Therefore, if the outer edge 18e1 of the bottom surface of the separator 18 is chamfered, even if burrs are generated, it is possible to prevent a problem that fragments and the like adhere to the bottom surface 18e of the separator and unnecessary projections and the like are formed. Can be.

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

In FIG. 10, the ceramic separator 1
8 shows a third embodiment of an assembled state of the heating element 8 and the heating element 3. In this embodiment, protruding surfaces F1, F1 protruding spherically toward the other side are formed on the end surface 3c of the heating element and the bottom surface 18e of the separator, respectively. Both protruding surfaces F1, F1
The point contact state is more easily obtained at the tip of the, and the occurrence of chipping, cracks and the like is suppressed.

In FIG. 10, the heating element side lead wire insertion hole 18a2 and the heater terminal accommodating portion 72d and the central communication portion 7
A partition wall 100 is formed between the partition wall 2e and the partition wall 100. A radial communication hole 101 is opened in the partition wall 100 so that the heating element-side lead wire insertion hole 18a2 and the central communication portion 72e communicate with each other. The separator 18 is connected to the heater terminal 3b.
Is formed as a gap forming portion S by forming a widening portion 3b2 which expands in a tapered shape (for example, a U-shape) outward in the radial direction with respect to the bottom surface outer edge 18e1. Heater terminal 3 in this case
The expanded portion 3b2 of b may be plastically deformed before the step of inserting it into the heater terminal accommodating portion 72d and the heating element side lead wire insertion hole 18a2.

Next, FIG. 11 shows a modification of the first embodiment shown in FIG. Among them, in FIG. 11A, the outer edges 18e1 and 3c of the separator bottom surface 18e and the heating element end surface 3c are shown.
1 shows an example in which chamfers 18e2 and 3c2 are formed in order to prevent chipping, cracks and the like in No. 1. In (b), a projecting surface F1 (radius of curvature R1) projecting spherically toward the heating element end face 3c side is formed on the separator bottom face 18e, and a spherical shape corresponding to the projecting face F1 is formed on the heating element end face 3c. (The radius of curvature R2 ≧ R1) is formed. In this case, a chamfer 3c2 may be formed on the outer peripheral portion of the end surface 3c of the heating element (see detailed example 1), or a spherical surface having a radius r may be formed (see detailed example 2).

FIG. 12 shows a modification of the second embodiment shown in FIG. In FIG. 12A, a protruding surface F1 that protrudes spherically toward the separator bottom surface 18e is formed on the heating element end surface 3c, and the separator bottom surface 18e is formed in a planar shape. In FIG. 9B, as the gap forming portion S, the convex portion 18f is formed on the central skeleton portion 18f of FIG.
1 instead of forming the elastic support portion 3 on the heater terminal 3b.
b3 is formed. The elastic support portion 3b3 is formed on the heater terminal 3b, extends forward from one end located on the rear side in the center axis O2 direction, and extends inside the cut 3b4 reaching the other end on the rear side via the direction changing portion. Tongue piece 3 located
b5 is formed by raising the heating shaft 3 in the insertion direction with the support shaft 3b6 positioned on the rear side as a fulcrum. Due to the elastic force of the elastic support portion 3b3, the heater terminal 3
b is prevented from protruding from the heating element side lead wire insertion hole 18a2.

In FIGS. 11 and 12, parts common to the corresponding figures (FIG. 8 or FIG. 9) are denoted by the same reference numerals and description thereof is omitted. In FIG. 12B, an enlarged view of a portion X2 is common to FIG.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of an oxygen sensor according to the present invention.

FIG. 2 is a partially enlarged longitudinal sectional view of the oxygen sensor of FIG. 1;

FIG. 3 is an exploded perspective view showing a state of being assembled to a ceramic separator.

FIG. 4 is a vertical cross-sectional view showing a state in which a heating element is attached to an oxygen detection element.

FIG. 5 is a plan view and a front half sectional view of the outer cylinder.

FIG. 6 is a plan view, a bottom view, and AA and BB sectional views of a ceramic separator.

FIG. 7 is an exploded perspective view showing an assembled state of the grommet and the ventilation section.

FIG. 8 is a longitudinal sectional view of the first embodiment showing an assembled state of the ceramic separator and the heating element.

FIG. 9 is a longitudinal sectional view of the second embodiment showing an assembled state of the ceramic separator and the heating element.

FIG. 10 is a longitudinal sectional view of a third embodiment showing an assembled state of a ceramic separator and a heating element.

FIG. 11 is a longitudinal sectional view showing a modification of FIG. 8;

FIG. 12 is a longitudinal sectional view showing a modification of FIG. 9;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Oxygen sensor 2 Oxygen detecting element 2a Hollow part 3 Heating element 3a Heating part 3b Heater terminal 3b1 Base end part 3b2 Expanding part 3b3 Elastic support part 3b4 Cut 3b5 Tongue piece 3b6 Raised support shaft 3c Rear end face (heat element end face) 3c1 3c2 Chamfer 9 Metal shell 16 Outer cylinder 17 Grommet 17a1 Detector element lead wire insertion hole 17a2 Heating element side lead wire insertion hole 18 Ceramic separator (separator) 18a1 Detector element side lead wire insertion hole 18a2 Heater element lead wire insertion hole (Lead wire insertion hole) Hole 18e bottom surface (separator bottom surface) 18e1 outer edge (bottom outer edge) 18e2 chamfer (chamfered portion) 18f central skeleton portion 18f1 convex portion 20, 21 detection element side lead wire 19, 22 heating element side lead wire (lead wire) 23 first terminal Hardware (pressing member) 72 Terminal accommodation hole 7 2e Central communication part (heating element end receiving hole) F1 projecting surface F2 concave surface S gap forming part O1 center axis of heating element O2 center axis of separator R1 radius of curvature of projecting surface F1 R2 radius of curvature of concave surface F2

Claims (9)

[Claims] 1. An oxygen detecting element having a front end portion in the form of a hollow shaft with a closed end, the front end portion being directed to a gas to be measured, and an oxygen detecting element disposed in a hollow portion of the oxygen detecting element and heating the oxygen detecting element. A shaft-like heating element, which is disposed substantially coaxially with the hollow portion on the rear side of the oxygen detection element, and has a front end face opened and a rear end portion of the heating element inserted therein. A separator having a hole, the heating element end receiving hole has a bottom surface at an intermediate position in the axial direction of the separator, and extends from the rear end side of the heating element inserted into the heating element end receiving hole. A lead wire insertion hole through which a heater terminal to be output and a lead wire connected to the heater terminal can be inserted is communicated in the circumferential direction with the heating element end receiving hole, and is inserted through the lead wire insertion hole. The heater terminals to be In order to prevent the outer edge of the bottom surface of the heating element end portion receiving hole from contacting and interfering with the outer edge of the bottom surface (hereinafter, referred to as the outer edge of the bottom surface), the heater terminal and the outer edge of the bottom surface are perpendicular to the axis. An oxygen sensor, wherein a gap forming portion that forms a certain amount of gap is formed in the heater terminal and / or the separator. 2. The heating element according to claim 2, wherein the lead wire insertion hole penetrates through the separator in the axial direction, and a front end side in the axial direction communicates with the heating element end accommodating hole at the outer periphery of the bottom surface. The oxygen sensor according to claim 1, wherein the oxygen sensor is integrated with the unit accommodation hole. 3. The gap forming section is formed in the heater terminal having a base end fixed to a rear end side of the heating element, and is continuously or stepwise expanded radially outward with respect to the bottom outer edge. The oxygen sensor according to claim 1, wherein the oxygen sensor is an expanding portion that opens. 4. The oxygen sensor according to claim 1, wherein the gap forming portion is a chamfered portion provided on an outer edge of the bottom surface of the separator and having a predetermined inclination with respect to the axis. 5. The center frame of the separator, which is surrounded by the bottom surface of the heating element end receiving hole and the lead wire insertion hole, in a direction intersecting with the axis. The oxygen sensor according to claim 1, wherein the oxygen sensor is a protrusion protruding from the portion into the lead wire insertion hole. 6. The gap forming portion is formed in the heater terminal, extends in a predetermined direction from one end, and moves the tongue piece located inside a cut reaching the other end through a direction changing portion to the heat generating portion. 3. The oxygen sensor according to claim 1, wherein the oxygen sensor is an elastic supporting portion which is formed in a direction in which the body is inserted. 7. The elastic support portion is formed by raising a support shaft on the rear side in the axial direction and raising the tongue piece positioned on the front side of the support shaft. Oxygen sensor. 8. The bottom surface (hereinafter, referred to as a separator bottom surface) of the heating element end receiving hole formed in the separator.
And a rear end face of the heating element (hereinafter, referred to as a heating element end face) is disposed so as to face each other, and at least one of the separator bottom face and the heating element end face is continuously reduced in cross section at the leading end side in the facing direction. The oxygen sensor according to any one of claims 1 to 7, wherein the oxygen sensor has a protruding surface that protrudes. 9. The oxygen sensor according to claim 8, wherein the bottom surface of the separator and the end surface of the heating element abut on each other in a point-like contact state at a tip of the protruding surface.