JPH0660883B2 - Oxygen sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an oxygen sensor which is attached to, for example, an exhaust pipe of a vehicle and is preferably used for detecting the oxygen concentration in exhaust gas.

[Conventional technology]

Generally, in an engine of an automobile or the like, a mixture of air and fuel is burned (exploded) in a combustion chamber to obtain a desired output. Therefore, a mixture ratio of air and fuel, that is, an air-fuel ratio. Is small (fuel is rich), incomplete combustion occurs, and conversely, if the air-fuel ratio is large (fuel is thin), the output is reduced.

Therefore, in recent automobiles and the like, an oxygen sensor (O ₂ sensor) is attached to an exhaust pipe or the like to detect the oxygen concentration in the exhaust gas, and thereby the air-fuel ratio is feedback-controlled.

Therefore, FIG. 3 shows a conventional oxygen sensor.

In the figure, reference numeral 1 denotes a sensor body formed of a metal material such as stainless steel in a cylindrical shape.
A stepped tubular holder 2 in which a male screw portion 2A as a mounting portion is formed on the outer peripheral side of the tip portion and a fitting portion 2B is formed on the base end side.
And the tip side is fixed to the outer peripheral side of the fitting section 2B of the holder 2 by the caulking sections 3A, 3A, ...
The stepped tubular cap 3 is provided with a diameter-reduced portion 3C via B, and a shoulder portion 2C that engages with a zirconia tube 5 described later is formed on the inner peripheral side of the tip portion of the holder 2. Then, the sensor body 1 includes the male screw portion 2A of the holder 2.
Is screwed onto an exhaust pipe (not shown) of the vehicle, so that the zirconia tube 5 and the like are arranged in the exhaust pipe in a state of being radially projected.

Reference numeral 4 denotes an insulating cylindrical body disposed inside the sensor body 1. The insulating cylindrical body 4 is formed of a ceramic material such as alumina into a stepped cylindrical shape, and one end side thereof is inside the reduced diameter portion 3C of the cap 3. The other end is inserted into the fitting portion 2B of the holder 2. The insulator 4 is arranged to insulate the sensor body 1 and the contact plate 10 described later.

Reference numeral 5 denotes a zirconia tube whose one end side is engaged with the shoulder portion 2C of the holder 2 via a ring-shaped washer 6 and the other end side is projected to the outside of the holder 2 in the axial direction. The zirconia tube 5 is a ceramic such as zirconium oxide. The material is formed into a U-shaped cross section, and one end thereof has a large-diameter opening 5A.
And the protruding end is the closed end 5B. When a difference in oxygen concentration between the inside and the outside of the zirconia tube 5 occurs, oxygen ions will pass through the zirconia tube 5, and the zirconia tube 5 will generate a detection signal between the outer electrode 7 and the inner electrode 8 described later as a detection signal shown in FIG. It is designed to generate electricity. In addition,
Porous platinum (not shown) is coated on the outer surface of the zirconia tube 5 so that the electromotive force is amplified (catalyst).

Reference numerals 7 and 8 denote an outer electrode and an inner electrode provided on the outer surface and the inner surface of the zirconia tube 5, respectively.
For the inner electrode 8, a metal material such as platinum is used for the zirconia tube 5.
The outer electrode 7 is formed by being attached to the outer surface and the inner surface of the holder 2 by means of coating or the like, and the outer electrode 7 is connected to the shoulder portion 2C of the holder 2 via the washer 6 and is grounded. The inner electrode 8 extends from the inner surface side of the closed end 5B of the zirconia tube 5 to the end surface side of the opening 5A as a lead portion 8A, and the lead portion 8A is connected to a contact plate 10 described later. Reference numeral 9 denotes a protector formed in a cylindrical shape with a cover so as to protect the protruding end side of the zirconia tube 5, and the protector 9 has the tip end side of the holder 2
It is fixed by caulking to the tip side of and is positioned substantially coaxially with the zirconia tube 5. A plurality of elongated holes 9A, 9A, ... Are formed on the peripheral surface of the protector 9, and each elongated hole 9A introduces the exhaust gas in the exhaust pipe to the outer surface side of the zirconia tube 5. There is.

Reference numeral 10 denotes a contact plate arranged in the insulating cylindrical body 4 so as to extend in the axial direction. The contact plate 10 is formed by bending a single metal plate made of stainless steel or the like by means of a press or the like. A connecting portion 10A for a lead wire 11 described later is provided on one end side thereof, and a disc-shaped contact portion 10B is provided on the other end side thereof. The contact portion 10B is strongly sandwiched between the end surface of the opening portion 5A of the zirconia tube 5 and the end surface of the insulating tubular body 4 by the spring load of the disc spring 12 described later, and is connected to the inner electrode 8. . Since the contact portion 10B is formed into a disc shape by the bending process, a small cutout portion 10C or the like is provided on the center side thereof.

11 is the connecting portion 10A of the contact plate 10 on the tip side.
Shows a lead wire connected to the outside of the sensor body 1, and the lead wire 11 uses an electromotive force generated in the zirconia tube 5 as a detection signal to connect an external control unit via the inner electrode 8 and the contact plate 10. (Not shown). Reference numeral 12 denotes a disc spring disposed between the stepped portion 3B of the cap 3 and one end side of the insulating tubular body 4. The disc spring 12 is formed by a disc spring, and the zirconia tube 5 is formed via the insulating tubular body 4. The outer peripheral side of the opening 5A is pressed against the shoulder 2C of the holder 2 and a clamping force or the like is applied to the contact portion 10B of the contact plate 10.

Further, 13 is a rubber tube that seals the periphery of the lead wire 11. The rubber tube 13 is made of fluororubber or the like, and the lead wire 11 and one end side of the insulating cylindrical body 4 and the reduced diameter portion 3C of the cap 3 are provided. Is inserted between and.
The rubber tube 13 prevents rainwater and the like from entering the sensor body 1 and the insulating cylinder 4 from around the lead wire 11.

The oxygen sensor according to the prior art has the above-described configuration. The sensor body 1 is screwed to the exhaust pipe of the vehicle through the male screw portion 2A of the holder 2, and the tip side of the zirconia tube 5 is inside the exhaust pipe together with the protector 9. It is fixed in the state that it protrudes. Then, the exhaust gas in the exhaust pipe is introduced around the zirconia tube 5 through each long hole 9A of the protector 9. At this time, since the exhaust gas is a waste gas obtained by burning a mixture of air and fuel, the oxygen concentration in the exhaust gas is low, and the exhaust gas between the atmosphere inside the zirconia tube 5 and the exhaust gas outside is reduced. A large difference occurs in the oxygen concentration.

Therefore, an electromotive force is generated between the outer electrode 7 and the inner electrode 8 of the zirconia tube 5, and this electromotive force is output as a detection signal to the control unit via the contact plate 10 and the lead wire 11 to obtain the air-fuel ratio. Is used for feedback control. In this case, as shown in FIG. 4, when the air-fuel ratio is small, the detection signal shows that the fuel becomes excessively rich and incomplete combustion occurs, so that the oxygen concentration in the exhaust gas significantly decreases, and 700 to 900 mV is obtained. On the contrary, when the air-fuel ratio becomes large, the fuel becomes lean and oxygen that is not involved in combustion remains in the exhaust gas. Therefore, the oxygen concentration does not decrease so much and suddenly rises to about 50-60 mV. Descend to. Then, this air-fuel ratio is feedback-controlled by the control unit so that the detection signal is maintained at about 500 mV.

[Problems to be solved by the invention]

By the way, in the above-mentioned conventional technique, the rubber tube 13 is inserted between the lead wire 11 and the reduced diameter portion 3C of the cap 3 to seal the periphery of the lead wire 11. Since it is made of fluororubber or the like, the high heat of the engine causes the exhaust pipe, the holder 2,
The rubber tube 1 through the cap 3 and the insulating cylinder 4
3 has a drawback that the rubber tube 13 is deteriorated at an early stage, the periphery of the lead wire 11 cannot be sealed, and rainwater or the like from the outside enters the inside.

Moreover, since the holder 2 and the cap 3 are merely fixed by the respective caulking portions 3A, the fitting portion 2B of the holder 2 is fixed.
Rainwater and the like from the outside may intrude into the inside from between the caulking portion 3A side of the cap 3 and the caulking portion 3A side, which causes a characteristic defect or the like.

Further, the contact plate 10 for the lead wire 11
Since the connecting portion 10A of the contact plate 10 is located inside the insulating cylinder 4, the contact plate 10 connects the connecting portion 10A to the lead wire 11
In addition to the drawback that the assembly work cannot be automated because it must be inserted into the insulating cylindrical body 4 together with the lead wire 11 after it is connected to the core wire by caulking, the overall size becomes large and the material cost becomes high. There is a drawback that it invites up.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and can improve heat resistance by eliminating the need for a mule tube or the like, prevent external rainwater, etc. from entering, and automate or miniaturize assembly work. It is intended to provide an oxygen sensor capable of achieving the above-mentioned, and surely reducing the material cost and the like.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention has a cylindrical holder in which the tip end outer peripheral side serves as a mounting portion for a vehicle, and the base end side is bent inward in the radial direction to form an annular bent portion. A stepped cylindrical insulating cylinder having a large diameter part inserted into the holder and a small diameter part protruding to the outside through a bent part of the holter, and one end of the insulating cylinder on the inner peripheral side of the tip of the holder. A zirconia tube that is attached so as to contact the body and has the other end protruding outside the holder to form a closed end, and outer electrodes provided on the outer surface and the inner surface of the zirconia tube, respectively.
The inner electrode is disposed inside the insulating cylinder, and one end of the inner electrode projects from the small diameter side of the insulating cylinder to the outside, and the other end is sandwiched between the zirconia tube and the insulating cylinder. And a cap attached to the small diameter portion of the insulating cylinder to seal between one end side of the contact plate and the small diameter portion side of the insulating cylinder. There is.

[Work]

The small-diameter portion side of the insulating tubular body is projected to the outside through the bent portion of the holder, and is projected to the outside of one end side of the contact plate from the small diameter portion side, and the small-diameter portion is provided between the one end side and the small-diameter portion side. Since it is configured to seal with the cap attached to the portion, high heat from the outside is merely transmitted to the cap through the insulating cylinder, heat resistance can be improved, and the sealing action can be maintained for a long period of time. Further, after the contact plate is inserted into the insulating cylinder, the lead wire can be connected to the one end side protruding to the outside, and the assembling work can be automated. Furthermore, the sensor main body can be configured by the holder, and the size can be reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. In the embodiment, the same components as those of the prior art shown in FIG. 3 described above are designated by the same reference numerals and the description thereof will be omitted.

In the figure, reference numeral 21 denotes a holder that constitutes the sensor main body. The holder 21 is formed in a stepped cylindrical shape by a metal material such as stainless steel, and is a male screw provided on the outer peripheral side of the tip portion as a mounting portion for a vehicle. 21A and the protector 9 on the tip end surface
21B for fixing the distal end side of the, a shoulder portion 21C provided on the inner peripheral side of the distal end portion, the outer peripheral side of which is engaged with the opening 5A of the zirconia tube 5 via the washer 6, and a thick wall provided on the intermediate portion. The tubular portion 21D and a thin tubular portion 21E axially extending from the base end side of the thick tubular portion 21D are roughly configured (see FIG. 2).

The base end side of the thin-walled tubular portion 21E is bent inward in the radial direction to form an annular bent portion 21F after insertion of an insulating tubular body 22 described later, and the bent portion 21F is a disc spring described later. The insulating cylinder 22, the zirconia tube 5 and the like are positioned in the holder 21 together with 25. Further, a heating caulking portion 21G formed by axially pressurizing with a load of, for example, about 350 kg / cm ² while electrically heating is provided in the middle portion of the thin-walled tubular portion 21E. 21G reduces the disk spring 25 by reducing the axial length of the thin-walled tubular portion 21E.
Is put in a compressed state.

Reference numeral 22 denotes an insulating cylindrical body in which the large diameter portion 22A side is inserted into the holder 21 and the small diameter portion 22B side protrudes outside through the bent portion 21F of the holder 21, and the insulating cylindrical body 22 is made of a ceramic material such as alumina. It is formed as a stepped tubular body composed of a large diameter portion 22A and a small diameter portion 22B. The tip surface of the large-diameter portion 22A is in contact with the end surface of the opening 5A of the zirconia tube 5 which will be described later.
Holding the contact portion 23B of the
Is connected to the lead-out portion 8A of the inner electrode 8. Further, an annular groove 22C is formed on the outer peripheral side of the small diameter portion 22B, and a cap 26 described later is engaged with the annular groove 22C by means of caulking or the like.

Reference numeral 23 denotes a contact plate arranged in the insulating cylindrical body 22 so as to extend in the axial direction. The contact plate 23 is formed by bending a single metal plate made of stainless steel or the like using a means such as a press. And a long connecting portion 23A is provided on one end side thereof, and a disc-shaped contact portion 23B is provided on the other end side thereof. Further, the contact plate 23 is formed with a curved portion 23C which is located closer to the contact 23B side and which projects outward in the radial direction. The curved portion 23C is formed when the contact plate 23 is inserted into the insulating cylindrical body 22. Further, the contact plate 23 is elastically engaged with the inner peripheral surface thereof to position the contact plate 23 in the insulating cylindrical body 22. The connecting portion 23A of the contact plate 23 is a small diameter portion 22B of the insulating cylindrical body 22.
From the side to the outside, and a lead wire 24 described later is connected to the protruding end side.

Reference numeral 24 denotes a lead wire connected to the protruding end side of the connecting portion 23A of the contact plate 23 by means of caulking or the like,
The lead wire 24 outputs the electromotive force generated in the zirconia tube 5 as a detection signal to an external control unit via the inner electrode 8 and the contact plate 23.

Reference numeral 25 denotes a disc spring arranged between the bent portion 21F of the holder 21 and one end of the large diameter portion 22A of the insulating cylinder 22. The disc spring 25 is formed by a disc spring or the like, and is a thin-walled cylinder of the holder 21. When the heat-crimped portion 21G is formed on the portion 21E, it is placed in a compressed state as shown in the drawing. And the disc spring 25
Is the opening 5 of the zirconia tube 5 through the insulating cylinder 22.
The A side is pressed against the shoulder portion 21C of the holder 21, and a clamping force is applied to the contact portion 23B of the contact plate 23, so that the contact portion 23B is pulled out by the lead portion 8A of the inner electrode 8.
It is designed to make sure contact with.

Further, 26 is a connecting portion 23A of the contact plate 23.
A cap that seals between the protruding side and the small diameter portion 22B of the insulating cylindrical body 22 is shown. The cap 26 is formed of a metal material such as stainless steel in a stepped cylindrical shape, and is rolled into the annular groove 22C of the small diameter portion 22B. It is fixed by using such means. Then, one end side of the cap 26 becomes a reduced diameter portion 26A that is radially inwardly reduced to the protruding side of the connecting portion 23A by means such as roll caulking, and the reduced diameter portion 26A is the protruding side of the connecting portion 23A. By closely adhering to, the outside rainwater and the like can be prevented from entering from the surroundings. The other end of the cap 26 is separated from the bent portion 21F of the holder 21 so as to be in an insulating state.

The oxygen sensor according to the present embodiment has the above-described configuration, and the basic operation thereof is not different from that of the prior art.

However, in this embodiment, the holder 21 is integrally formed with the thin-walled tubular portion 21E to configure the sensor body only with the holder 21, and the bent portion 21F of the holder 21 to the small-diameter portion 22B side of the insulating tubular body 22. The small diameter portion 2
Cap 26 attached to 2B through annular groove 22C
As a result, the periphery of the connection portion 23B of the contact plate 23 is sealed via the reduced diameter portion 26A, so that the cap 26 can prevent rainwater and the like from entering the inside. Since high heat from the engine or the like is transmitted to the cap 26 only through the insulating cylindrical body 22 made of a ceramic material, the cap 26 can be prevented from being in a high temperature state as much as possible, and the cap 26 is made of metal. Since it is made of a material, its heat resistance can be greatly improved, and its sealing action can be maintained for a long time.

Further, since the disc spring 25 is arranged in a compressed state between the bent portion 21F of the holder 21 and the large diameter portion 22A of the insulating cylindrical body 22, the gap between the disc spring 25 and the cap 26 can be sealed. At the same time, it is possible to reliably prevent rainwater from entering.

Further, since the contact plate 23 has the connecting portion 23A projected to the outside and is connected to the lead wire 24 on the protruding end side, the contact plate 23 is disposed in the insulating cylindrical body 22 and the inside of the holder 21 is disposed. Connection part 23
Since the lead wire 24 can be connected to the protruding end side of A, the assembly work of the oxygen sensor can be completely automated. In this case, the contact plate 23 is provided with a curved portion 23C, and the contact plate 23 is attached to the insulating cylindrical body 2.
Since the contact plate 23 is positioned in the insulating cylindrical body 22 by the curved portion 23C when it is inserted into the inside 2, the heating caulking portion 21G is formed in the thin-walled cylindrical portion 21E of the holder 21, and the disc spring 25 is formed. When compressing the contact plate 23, the contact plate 23
It is possible to prevent the positional deviation inside, and to more reliably promote automation of the assembly work.

In addition, as compared with the prior art, the cap 3 shown in FIG.
In addition to being unnecessary, the axial dimension of the insulating cylindrical body 22 can be reduced, so that the oxygen sensor can be surely downsized, and material costs and the like can be reduced to achieve cost reduction.
Has various effects.

In the above embodiment, the disc spring 25 is provided between the bent portion 21F of the holder 21 and the large diameter portion 22A of the insulating cylindrical body 22, but the disc spring 25 does not necessarily have to be provided. In this case, when forming the heating caulking portion 21G in the thin-walled tubular portion 21E of the holder 21, the bent portion 21F directly presses the large-diameter portion 22A of the insulating tubular body 22 in the axial direction to form a zirconia tube. You may make it give a pressing force to 5 grade | etc.,.

〔The invention's effect〕

As described above in detail, according to the present invention, the small diameter portion side of the insulating cylindrical body is projected to the outside through the bent portion of the holder, and one end side of the contact plate is projected to the outside from the small diameter portion side. Since the gap between the one end side and the small diameter portion side is sealed by the cap attached to the small diameter portion, the heat resistance is improved, the sealing action can be maintained for a long time, and rainwater etc. can enter inside. Can be prevented. Further, after the insulating cylinder, the contact plate, etc. are assembled in the holder, the lead wire can be connected to one end side of the contact plate protruding to the outside, and the assembling work can be automated. Further, the oxygen sensor can be downsized, and the cost can be reduced.

[Brief description of drawings]

1 and 2 show an embodiment of the present invention, FIG. 1 is a vertical sectional view of an oxygen sensor, FIG. 2 is a vertical sectional view of a holder, and FIGS. 3 and 4 are prior arts. FIG. 3 is a vertical sectional view of the oxygen sensor, and FIG. 4 is an output characteristic diagram of a detection signal. 5 ... Zirconia tube, 5A ... Opening, 7 ... Outer electrode, 8 ... Inner electrode, 21 ... Holder, 21A ...
Male thread, 21C ... Shoulder, 21E ... Thin-walled cylinder, 21
F ... Bent portion, 21G ... Heating caulking portion, 22 ... Insulating cylinder, 22A ... Large diameter portion, 22B ... Small diameter portion, 23 ...
… Contact plate, 23A …… Connection part, 23B ……
Contact part, 23C ... curved part, 24 ... lead wire,
25 ... Disc spring, 26 ... Cap, 26
A: Reduced diameter section.

Claims (1)

[Claims] 1. A cylindrical holder in which the outer peripheral side of the tip portion is a mounting portion to a vehicle, and the base end side is bent radially inward to form an annular bent portion, and the large diameter portion side is inside the holder. The stepped cylindrical insulating cylinder is inserted into the holder, the small diameter side of which protrudes to the outside through the bent portion of the holder, and the one end of the holder is attached to the inner peripheral side of the tip of the holder so as to abut the insulating cylinder. A zirconia tube having the other end protruding outside the holder to form a closed end, an outer electrode and an inner electrode respectively provided on the outer surface and the inner surface of the zirconia tube, and disposed inside the insulating cylinder, and one end of the insulation A contact plate that protrudes outward from the small diameter portion side of the tubular body, and has the other end sandwiched between the zirconia tube and the insulating tubular body and connected to the inner electrode, and one end side of the contact plate and the insulating tubular body. With the small diameter side of the body In order to seal, the oxygen sensor comprising consist of a cap attached to the small diameter portion of the insulating cylinder.