JPH0833369B2 - Oxygen sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor, and more particularly to an oxygen sensor provided in an exhaust gas system of a vehicle (hereinafter referred to as vehicle oxygen sensor).

(Prior Art and Problems) A vehicle oxygen sensor has a bag-shaped solid electrolyte element, a pair of electrodes is provided on the inner and outer surfaces of the element, and the inner electrode (reference electrode) is used as a reference oxygen gas. The electrode on the outer surface (measurement electrode) is brought into contact with the oxygen gas to be measured, and a potential difference is generated between the two electrodes in response to the oxygen concentration difference between the inside and outside of the element. There are those that detect.

In such a vehicle oxygen sensor, its housing is attached to an exhaust gas system manifold, and one electrode (usually a reference electrode) is connected to a control circuit while the other electrode (usually a measurement electrode) is housed in the exhaust gas system. It was common to ground through the system (for example, Japanese Examined Patent Publication No. 59-41952).

However, in this type of oxygen sensor, since the output is weak, it is affected by some noise of the engine system, for example, noise due to the spark plug or noise due to the potential difference of the ground current, and accurate detection is not possible. It has a problem that it is difficult.

On the other hand, the other electrode (usually the measurement electrode) is also electrically insulated from the housing so as to be guided to the control circuit side so that noise is not mixed in. JP-A-51-103494 and JP-A-60-18
It is proposed in Japanese Patent No. 3857. However, these materials are unsatisfactory in practical use because they are used at high temperatures.

(Object) In view of the problems of the prior art, an object of the present invention is to suppress the output of the oxygen sensor from being influenced by noise of the engine system even at a high temperature as much as possible, so that the oxygen sensor for the vehicle always provides accurate oxygen. It is to be able to detect the concentration.

(Means for Solving Problems) In the oxygen sensor of the present invention, the other end is the detection unit (4a),
A solid electrolyte element (4) having a rear part as an output extraction part (4b) and a flange part (4c) projecting outward in the middle part;
A pair of electrodes provided on the inner and outer surfaces of the outer element in the detection section, and a wire that is provided on the outer surface of the element and has its tip connected to the rear end of the electrode provided on the outer surface and the rear end reaching the output extraction section. Portion (8 ') formed in a strip shape, a strip shape or a film shape, and a connecting means for electrically connecting the lead portion in the output extraction portion (4b) and an external lead, and form a tubular body as a whole. A taper step portion (13a) on the inner surface and a caulking portion (13b) on the rear end, and a solid electrolyte element (4) having an electrode and a lead portion (8 ') can be inserted coaxially therewith. Part (4c) is tapered step (13a) and crimped part (1
3b) The mounting metal fitting (13) for gripping by being strongly pressure-inserted in the axial direction, and the electrical insulation between the element lead portion (8 ') and the mounting metal fitting (13). An oxygen sensor, comprising: an insulator unit (17) interposed in an annular space between a solid electrolyte element (4) and a mounting metal member for securing the insulator unit (17) Surface facing the tip of the collar (4c) of the electrolyte element and the taper step (13
a), the front cylindrical insulator (18) made of a ceramic sintered body that is strongly pressed in the axial direction so as to directly act on the protruding shoulder surface on the front side of the flange, and the crimping portion and the collar. An intermediate cylindrical insulator (19) made of compression-filled ceramic powder, which is strongly pressed in the axial direction so as to directly act on the projecting shoulder surface on the rear side of the flange between the surface facing the rear of the portion, and It is characterized by comprising a rear cylindrical insulator (20) made of a ceramic sintered body, which is strongly pressed in the axial direction from a mounting member and axially strongly presses the intermediate cylindrical insulator (19).

(Embodiment) (1) The lead preferably extends in a strip shape along the front-back direction of the outer surface of the element.

The material of the lead part is a noble metal such as platinum (Pt)
Is mentioned.

(2) As the insulator, as an insulator positioned further ahead of the collar portion of the element, an insulator positioned further rearward, and an elastic member and an airtight sealing material disposed in the middle thereof. It is preferable to use a divided structure composed of the compression-filled ceramic powder of (1).

As the material of the insulator, ceramic, which is advantageous in high temperature electric insulation and strength, is used.

(3) Since it is not necessary to use a material such as graphite that reacts with oxygen at a high temperature (600 ° C. or higher) as a conductive material that transmits the potential from the reference electrode and the measurement electrode, a high temperature (especially 600 The oxygen sensor of the present invention is suitable for use at temperatures above (° C.).

(Operation) With such a configuration, the lead portion on the outer surface of the element can maintain sufficient electrical insulation with respect to the housing even at a high temperature of 600 to 800 ° C. and can be output (grounded) to the outside of the housing. The solid electrolyte element is always fixed to the mounting metal fittings under high temperature and strong vibration, and the repulsive force always acts like a spring action and is fixed, thus providing good airtightness, insulation and necessary electrode terminal connectivity. It is held and fixed.

(Example) Hereinafter, the Example of this invention is described based on drawing.

In FIGS. 1 to 4, reference numeral 1 denotes an oxygen sensor, which is attached to an exhaust gas manifold 2 of an engine system of a vehicle and a signal of which is output to a control circuit 3.

The oxygen sensor 1 includes a bag-shaped solid electrolyte element 4 that causes a partial pressure difference according to the oxygen gas concentration, a lead element 5 that outputs a signal based on the element 4 to the control circuit 3, the element 4 and the lead element. Housing 6 surrounding (part of) 5
It consists of and.

The element 4 has a detection part 4a at its tip, exhaust gas A is present outside thereof, and reference gas B is present inside thereof, so that an oxygen concentration difference can be caused by the exhaust gas A and the reference gas B. It has become. Further, the rear end portion thereof serves as an output extracting portion 4b, and the signal from the element 4 is transmitted from the output extracting portion 4b to the control circuit. In addition, 4c is a flange portion which is formed to project outward at the front-rear direction intermediate portion of the element 4.

The element 4 is provided with a porous reference electrode 7 on its inner surface and a porous measurement electrode 7'on its outer surface over the entire area in the circumferential direction of the detecting portion 4a so that a potential difference is generated based on the oxygen concentration difference. Has become.

The lead element 5 includes element leads 8, 8 ', external leads 9, 9'and an intermediate lead 10 as a connecting means for electrically connecting the element leads 8, 8'and the external leads 9, 9'. It consists of 10 '. The element leads 8 and 8'are provided on the inner and outer surfaces of the element 4, and the tips thereof are connected to the rear ends of the electrodes 7 and 7'and extend rearward along the shape of the element 4 in a strip shape to output the output. It has reached part 4b. On the other hand, the external leads 9 and 9 ′ extend from the control circuit 3 and are inserted into the rear end portion of the housing 6. Intermediate lead 10, 1
The reference numeral 0'is disposed in the housing 6 between the output extraction portion 4b of the element 4 and the insertion ends of the external leads 9, 9 ', and the pair of electrodes 7, 7'of the element 4 and the control circuit 3 are provided. And a pair of external leads 9 and 9 '. Here, the intermediate leads 10 and 10 'are made of a heat-resistant material having spring properties (for example, precipitation hardening stainless steel), and the tips thereof are spring-like strips 10a and 10'a, and at the output extracting portion 4b of the element 4. The strip 10a is fitted to the rear end of the element lead 8 so as to be pressed against the rear end of the element lead 8 by a spring force, and the radius of the strip 10'a relative to the rear end of the element lead 8 '. The electrodes 7, 7'and the intermediate lead are fitted so as to be pressed against each other depending on the spring force directed inward.
10 and 10 'are connected via element leads 8 and 8'. On the other hand, the rear ends of the intermediate leads 10 and 10 'are notched tubular bodies.
10b and 10'b, and the cylindrical bodies 10b and 10'b are fitted into the insertion ends of the external leads 9 and 9 ', respectively, so that the control circuit 3 and the intermediate leads 10 and 10' are externally connected. They are connected via leads 9 and 9 '. And the control circuit 3
At, the output associated with the measuring electrode 7'is grounded.

Here, on the outer surface side of the element 4, the porous protective layer 11 is laminated so as to cover the measuring electrode 7 ', and the measuring electrode 7'and the protective layer 11 are porous. The contact with the element 4 is ensured.

The housing 6 has a mounting bracket 13 fixed to the manifold 2, and the element 4 is provided in front of the mounting bracket 13.
While a protective cap 14 for preventing heat deterioration of the detection section 4a of the above is disposed, the rear side is surrounded by a part (insertion end) of the intermediate leads 10 and 10 'and the external leads 9 and 9'. 1 cylinder
15 and the second cylindrical body 16 are arranged. A caulking portion 13b is formed at the rear end of the fitting 13, and a taper step portion 13a is formed on the inner surface side.

An insulator 17 is interposed in the annular space between the element 4 and the mounting member 13 in order to ensure electrical insulation and thermal insulation between the element lead 8'and the mounting member 13. ing. The insulator 17 unit includes a front insulator 18, an intermediate insulator 19, and a rear insulator 20, which are sequentially located rearward from the front. The front insulator 18 is made of a ceramic (for example, alumina) sintered body and has a tapered portion 18a at the center of its inner surface.
It is a tubular body having a tapered portion 18b at the tip of the outer surface, and the inner tapered portion 18a abuts on the forward tapered portion of the collar portion 4c, while the outer tapered portion 18b abuts on the stepped portion 13a. The intermediate insulator 19 is a cylindrical body made of filled ceramic powder (for example, talc powder), and functions as a spring member or elastic member and an airtight sealing member for constantly exerting a repulsive force. The rear insulator 20 is made of a ceramic (for example, alumina) sintered body, and is a cylindrical body in which the rear end of the outer surface is the large diameter portion 20a, and the large diameter portion 20a is the rear end of the fitting 13. The maximum displacement in the front-rear direction is regulated by engaging with the portion (the inner diameter of which is slightly larger). Here, the rear end caulking portion 13b of the mounting member 13 is caulked, and the rear insulator 20 and thus the intermediate insulator acting as an elastic member and an airtightness preventive member through the outward flange 15a at the tip of the first tubular body 15. While 19 presses the collar portion 4c of the element 4 from the rear, the stepped portion 13a of the mounting member 13 and thus the front insulator 18 presses the collar portion 4c from the front, so that the element 4 causes each of the insulators 18, 19 described above. , 20 with mounting bracket 13
Is held in place with respect to. In addition, 21 is a metal packing.

Further, between the cylindrical bodies 15 and 16 and the outer leads 9'or the intermediate leads 10 and 10 ', the insulator 2 is appropriately provided in the front-rear direction.
2 and 22 are installed.

In addition, 23 is a heater and 24 is a lead element related to the heater.

Next, regarding the oxygen sensor of the embodiment having such a configuration,
The action will be described.

Now, the potential difference based on the oxygen gas concentration difference is
7 '. Then, the signal from the reference electrode 7 is output to the control circuit 3 via the element lead 8, the intermediate lead 10 and the external lead 9. On the other hand, the signal from the measuring electrode 7'is the element lead 8'and the intermediate lead 10 '.
And it is output to the control circuit 3 via the external lead 9'and is grounded. Here, the output system of such a signal is
With regard to both of the electrodes 7 and 7 ', the housing (that is, the mounting bracket 13, the protective cap 14, and the cylindrical bodies 15 and 16) that can conduct to the engine system is an insulating element (that is, the insulating unit 17 and It is insulated by insulators 22, 22). Therefore, the output signal from the oxygen sensor 1 to the control circuit 3 via the lead element 5 is hardly affected by noise from the engine system. In particular, the mounting bracket 13 has a high temperature, but that portion is composed of a ceramic insulator unit, that is, a front tubular ceramic insulator 18, an intermediate tubular insulator 19 made of filled ceramic powder, and a rear tubular ceramic insulator. High electrical insulation performance (for example, 1 MΩ or higher) is easily obtained, and noise from the engine system is constantly prevented from mixing.

In addition, these insulators 18, 19 and 20 are solid electrolyte elements 4
Together with the flange 4c of the mounting bracket, the tapered stepped portion 13a and the crimped portion 13b.
Since it is fixed by axially interposing a strong pressure between it and the
It is possible to obtain an oxygen sensor that is robust and has good airtightness even under strong vibration.

(Other Embodiments) The signals related to the electrodes 7 and 7'may be grounded in any manner as long as they are not grounded through the housing 6 directly connected to the engine system.

For example, the signal output to the outside of the housing 6 by the external lead 9'may be grounded without passing through the control circuit 3. Further, the signal related to the reference electrode 7 may be grounded.

(Advantages of the Invention) As described above, according to the present invention, it is possible to solve the above-mentioned problems of the conventional technique and to improve the detection accuracy of the oxygen concentration by the oxygen sensor constantly and stably even at high temperatures. Has a remarkable effect.

In addition, the solid electrolyte element is caulked to the mounting bracket via the ceramic insulator unit that has the elastic member made of ceramic powder in the middle, so that it can always be surely insulated even under high temperature and strong vibration. Assembling is performed to maintain good airtightness.

In addition, by using the rear end of the lead portion adhesively formed on the outer surface of the solid electrolyte element as the output attachment portion of the outer electrode of the element, it is possible to reliably and easily take out the output (ground) to the outside. , Both positive and negative electrodes are insulated, electrical connection to the outside is reliably achieved, and the assembly structure of the oxygen sensor as a whole can be made compact.
Also, the assembly becomes easy.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing an example of a mounting position of an oxygen sensor according to the present invention, FIG. 2 is a partial sectional view showing an entire embodiment of the present invention, and FIG. FIG. 4 is a perspective view showing a lead state of the solid electrolyte element of the example, and FIG. 4 shows the insulator of the above-described embodiment (related to the mounting bracket).
FIG. 4 (a) is a perspective view showing a front insulator and FIG. 4 (b) is a rear insulator. 1 ... Oxygen sensor, 4 ... Solid electrolyte element, 4a ... Detection part, 4b ... Output extraction part, 4c ... Collar part, 6 ... Housing, 7, 7 '... Electrode (reference electrode, measurement electrode) ), 8 '... Lead (element lead provided on the outer surface), 13 ... Mounting bracket, 13a ... Tapered step portion, 13b ... Crimping portion 17 ... Insulator unit 18 ... Tip cylindrical insulator 19 …… Middle tubular insulator 20 …… Rear tubular insulator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-57-178152 (JP, A) JP-A-51-103494 (JP, A) Actually open Sho- 60-179862 (JP, U) Actual-open Sho-57- 86452 (JP, U) Actual development Sho 60-183857 (JP, U)

Claims (3)

[Claims] 1. A flange (4) having a detection part (4a) on the front side, an output extraction part (4b) on the rear side, and an outwardly projecting flange part at the middle part.
c) formed solid electrolyte element (4), a pair of electrodes provided on the inner and outer surfaces of the element in the detection part, an outer surface of the element, and a tip provided on the outer surface. A lead portion (8 ') which is connected to the rear end of the electrode and whose rear end is formed in a linear shape, a strip shape or a film shape to reach the output extraction portion, and the lead portion and the outside of the output extraction portion (4b). A connecting means for electrically connecting the lead, a tubular body as a whole, and a taper step portion (13a) on the inner surface and a caulking portion (13b) on the rear end are provided, and the electrode and the lead portion (8 ′) Is inserted into the solid electrolyte element (4) coaxially and the collar portion (4c) is axially formed between the taper step portion (13a) and the crimp portion (13b). Mounting bracket (13) for gripping by being strongly pressure-inserted in
And an annular space between the solid electrolyte element (4) and the mounting metal fitting in order to ensure electrical insulation between the element lead portion (8 ') and the mounting metal fitting (13). An oxygen sensor having a fixed insulator unit (17), wherein the insulator unit (17) has a surface facing the tip of the collar portion (4c) of the solid electrolyte element and a taper step portion of the mounting bracket. (13a) a front cylindrical insulator (18) made of a ceramic sintered body which is strongly pressed in the axial direction so as to directly act on the protruding shoulder surface on the front side of the collar portion, and the above-mentioned crimping. Intermediate cylindrical insulator made of compression-filled ceramic powder that is strongly pressed in the axial direction so as to directly act on the projecting shoulder surface on the rear side of the collar portion between the flange portion and the rearward facing surface of the collar portion. (19)
And a rear cylindrical insulator (20) made of a ceramic sintered body, which is strongly pressed in the axial direction from the mounting fitting to strongly press the intermediate cylindrical insulator (19) in the axial direction. And oxygen sensor. 2. The oxygen sensor according to claim 1, wherein said connecting means is provided with a strip of a heat-resistant material having a spring property in front of said strip after said element lead portion (8 '). An oxygen sensor, which is a metal intermediate lead, which is press-fitted to the output extraction portion (4a) of the solid electrolyte element (4) having the end portion by a spring force directed in the radial direction thereof. 3. The oxygen sensor according to claim 1 or 2, wherein the lead portion on the outer surface of the element is used in an environment where the temperature is 600 ° C. or higher.