JP2002039985A - 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 chipping, cracks, etc., in the bottom surface of a separator and the face of a heating element in assembly and during operation and avoiding the state of operation failures and inoperatable state, even in the case that the bottom surface of the separator and the face of the heating element are opposed to each other so that they can be brought into contact with each other. SOLUTION: At least one of the bottom surface 18e of the separator and the face 3c of the heating element opposite to each other comprises a protruded surface F1. The protruded surface F1 is capable of preventing the occurrence of chippings, cracks, etc., in the bottom surface 18e of the separator and the face 3c of the heating element which are opposite to each other which can be brought into contact with each other by a pressing force in assembly, vibrations during the operation of an internal combustion engine, etc. Therefore, it is possible to prevent the oxygen sensor 1 (oxygen-detecting element 2) from turning into a state of operational failures and inoperatable state, due to these fragments that have come off and to heighten the reliability and lengthen the product life of the oxygen sensor.

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 approach one side, the end face of the heating element is biased with respect to the separator bottom. You will come into contact in a state. Further, even if the heating element and the separator are not eccentric in design, the end face of the heating element and the bottom face of the separator may be in contact with each other due to a manufacturing error or an uneven pushing force at the time of assembly. As a result, chipping (cracking) or cracking (crack) occurs on at least one of the end surface of the heating element and the bottom surface of the separator due to a pushing force at the time of assembly, vibration during operation of the internal combustion engine, and the like. (Oxygen detecting element) may malfunction or become inoperable.

Accordingly, an object of the present invention is to prevent chipping and cracking from occurring on the separator bottom surface and the heating element end face during assembly and operation, even when the bottom face of the separator and the end face of the heating element are arranged so as to be in contact with each other. It is an object of the present invention to provide an oxygen sensor capable of preventing malfunction, avoiding a malfunction and an inoperable state, and realizing high reliability and product life.

[0007]

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 receiving hole into which a front end face is opened and a rear end of the heating element is inserted, and a bottom surface of the heating element end receiving hole located at an axially intermediate portion of the separator. (Hereinafter, referred to as a separator bottom surface) and a rear end face of the heating element (hereinafter, referred to as a heating element end face), and at least one of the separator bottom face and the heating element end face has a leading end side in the facing direction. And having a projecting surface that projects in a form that continues to transverse constriction.

According to the present invention, at least one of the bottom face of the separator and the end face of the heating element, which are arranged to face each other, has a protruding face. 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. . Therefore, it is possible to prevent a state in which the oxygen sensor (oxygen detection element) becomes inoperable or inoperable due to the dropped pieces, thereby improving the reliability and the product life of the oxygen sensor.

In the case where the bottom face of the separator and the end face of the heating element are in contact with each other, it is desirable that the tip end of the protruding face be in 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. In this specification, the point-like contact state refers to a point contact or a state similar thereto.

For example, in order to bring the heating element into contact with the inner wall surface of the hollow portion of the oxygen detecting element, the center axis of the heating element is arranged to be inclined with respect to the center axis of the separator. May be placed eccentrically so that However, when this protruding surface is formed on the bottom surface of the separator, it is possible to suppress the occurrence of chipping and cracks on the bottom surface of the separator and the end surface of the heating element, and to make it possible to rotate the end surface of the heating element relative to the protruding surface of the bottom surface of the separator. Become. Thereby, the twist between the separator and the heating element can be eliminated, and the manufacturing error and the like can be kept within a predetermined range.

As another example, a protruding surface can be formed on the end surface of the heating element, and a concave surface corresponding to the protruding surface formed on the end surface of the heating element can be formed on the bottom surface of the separator. As a result, the protruding surface of the end surface of the heating element can be slightly rotated relative to the concave surface of the separator bottom surface.
Therefore, the present invention exerts further effects in suppressing the occurrence of chipping, cracks, and the like on the bottom surface of the separator and the end surface of the heating element, and in eliminating kinks between the separator and the heating element. If the radius of curvature of the concave surface formed on the bottom surface of the separator is larger than the radius of curvature of the projecting surface formed on the end surface of the heating element, it is almost the same as a pivot bearing used for precision instruments such as instruments and watches. With the configuration, both surfaces can be rotated relatively smoothly.

In these examples, at least one outer edge of the bottom surface of the separator and the end surface of the heating element may be chamfered with a predetermined inclination with respect to the center axis. By chamfering the outer edge where chipping, cracks and the like are liable to occur and which are liable to fall off, it is possible to effectively prevent the occurrence of these and the scattering of the falling off pieces.

[0013]

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 body 33c, and is integrated with one end of a lead wire portion 33b connected to one circumferential position of the fitting 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. An 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 cylinder 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 becomes more 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 to 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. A flange-like separator-side support portion 18A having a circular cross section orthogonal to the shaft is formed on the outer peripheral surface on the rear end side in the axial direction so as to protrude outwardly 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.
At a position not interfering with the axis and in a direction orthogonal to 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 7d.
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 body 33c of the second connecting metal fitting 33 is formed on the opening-side 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 surface 53A2 (venting portion) of the filter 53A → the ventilation groove 18b of the ceramic separator 18 → the detecting element side lead wire insertion holes 18a1 and 18a1 and the detecting 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 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 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 a middle part following the base end part 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 18 and unnecessary protrusions are formed. Can be.

Further, a projection 18f1 projecting into the heating element side lead wire insertion hole 18a2 is formed on the central skeleton 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.

Also, 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 (10)

[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, a bottom surface of the heating element end accommodating hole located at an intermediate portion in the axial direction of the separator (hereinafter, referred to as a separator bottom surface),
A rear end face of the heating element (hereinafter, referred to as a heating element end face) is disposed so as to face, and at least one of the separator bottom face and the heating element end face protrudes in a form in which the front end side continuously decreases in cross section in the facing direction. An oxygen sensor having a protruding surface. 2. The oxygen sensor according to claim 1, wherein the bottom surface of the separator and the end surface of the heating element abut on a tip end of the protruding surface in a point-like contact state. 3. The oxygen sensor according to claim 1, wherein the protruding surface is formed on a bottom surface of the separator. 4. The oxygen sensor according to claim 3, wherein the projecting surface formed on the bottom surface of the separator has a spherical shape. 5. The oxygen sensor according to claim 1, wherein the projecting surface is formed on an end surface of the heating element. 6. The oxygen sensor according to claim 5, wherein a concave surface corresponding to a protruding surface formed on an end surface of the heating element is formed on a bottom surface of the separator. 7. The oxygen sensor according to claim 6, wherein an opening area of the concave surface formed on the bottom surface of the separator is larger than an axial cross-sectional area of a protruding surface on an end face side of the heating element at the opening position. 8. The oxygen sensor according to claim 6, wherein both the protruding surface formed on the end surface of the heating element and the concave surface formed on the bottom surface of the separator are spherical. 9. When the radius of curvature of the projecting surface formed on the end surface of the heating element is R1, and the radius of curvature of the concave surface formed on the bottom surface of the separator is R2, R1 ≦ R2 is satisfied. An oxygen sensor according to any one of claims 6 to 8. 10. A chamfer having a predetermined inclination with respect to a central axis is applied to an outer edge of at least one of the bottom surface of the separator and the end surface of the heating element.
The oxygen sensor according to any one of the above.