JPS6345060B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an oxygen sensor in which an oxygen sensor element is fixed to the tip of an insulating tube made of ceramic or the like, and includes an output extraction part for the inner electrode having a structure that allows the potential of the inner electrode to be reliably extracted. The present invention relates to an oxygen sensor.

An oxygen sensor is a solid electrolyte container (sensor element) in which inner and outer electrode layers made of platinum-based metal thin films are formed on the inner and outer surfaces of a container-shaped base material made of a solid electrolyte such as zirconia stabilized with yttrium oxide, etc. ), use a gas containing a certain amount of oxygen, such as air, as the internal standard substance, and calculate the ratio of the equilibrium oxygen partial pressure between the internal standard substance that contacts the inner and outer electrodes of the sensor element, and the gas to be measured. is converted into a potential difference, thereby detecting the oxygen concentration of the gas being measured.In automobiles, it plays the role of detecting the oxygen concentration in the exhaust gas, which is fed back to the air-fuel ratio control mechanism of the engine, and uses a three-way catalyst. It is indispensable for the exhaust gas purification system used.

A conventional oxygen sensor usually has a structure as shown in FIG. 1 when air is used as an internal standard substance. The element 1 consists of a solid electrode container in which inner and outer electrode layers 1b and 1c are formed on the inner and outer surfaces of a container-shaped base material such as zirconia stabilized with yttrium oxide or the like, and a housing made of a heat-resistant material such as heat-resistant steel. The inner and outer electrode layers 1b and 1c are separated and insulated at the outer surface or the end surface of the opening above the shoulder. The gap between the element 1 and the housing 2 is filled with a conductive ring 3 made of a heat-resistant conductor such as graphite, and further filled with a cushion ring 4 made of a heat-resistant material such as talc or asbestos.
The potential generated on the outer electrode layer 1c of the element 1 is transmitted to the housing 2 from above the shoulder portion 1a via the conductive ring 3. On the other hand, a stem 5 made of, for example, heat-resistant steel and having a through hole for introducing air is inserted into the opening of the element 1, and a gap between the inner surface of the element opening and the stem 5 is made of, for example, graphite. A conductive material 6 is filled. Further, a protective cover 7 is fixed to the upper part of the housing 2 by a protective cover positioning ring 8, and a rear insulating tube 9 made of a heat-resistant insulator such as alumina is held at the upper end of the protective cover 7. A potential extraction terminal 10 made of a conductor is fixed to the rear insulating tube 9. A coil-shaped spring 11 made of a heat-resistant elastic material and conductive material such as heat-resistant steel is installed between the terminal 10 and the stem 5.
It secures contact between the inner surface near the opening of the conductive material 6 and the conductive material 6 and the stem 5, and at the same time maintains the shape of the conductive material 6 so that it does not collapse due to vibration etc. The generated potential is
is transmitted to the terminal 10 from the inner surface near the opening via the conductive material 6, stem 5, and spring 11.

However, the conventional oxygen sensor in which the solid electrolyte container is held within the steel housing as described above has the following drawbacks.

(1) The element must be large in order to prevent the gas to be measured and the internal standard gas from mixing and to ensure a certain amount of protrusion into the gas to be measured.
Furthermore, since the heat-resistant conductor such as graphite, which also serves as a sealing material, does not have sufficient heat resistance, it must be installed at a location away from the measurement area that is exposed to the high-temperature gas to be measured, which requires the element itself to be large.

(2) Graphite and other materials used as heat-resistant conductors often have high thermal conductivity, so if an oxygen sensor is attached to the exhaust pipe of a car and water splashes onto the exposed part (lower half), the temperature caused by the water will drop. The drop is quickly transmitted to the element 1 via the housing 2 and the conductive ring 3. If such a situation occurs when the element 1 is in a high temperature state, the element 1 made of zirconia or the like, which is susceptible to thermal shock, will be destroyed.

In order to solve the above-mentioned drawbacks, the following proposals have been made. That is, as shown in FIGS. 2 and 3, the shoulder portion 20a is made of an oxygen ion conductive material such as zirconia stabilized with yttrium oxide or the like, and the shoulder portion 20a is formed such that the outer diameter near the opening is larger than the tip. It has a container-like shape, and inner and outer electrode layers 20b and 20c made of platinum alloy thin films are formed on the inner and outer surfaces, and if necessary, a porous coating layer is formed to protect the outer electrode layer (not shown). A cylindrical part made of a heat-resistant conductive material such as heat-resistant steel and having an inner diameter slightly larger than the outermost circumferential diameter of the element, and a diameter of the cylindrical part continuously reduced to form the outermost part of the element 20. an element contacting part 22a consisting of a tapered part smaller than the outer circumferential diameter and larger than the outer diameter of the tip of the element and having the same shape as the shoulder part 20a of the element 20; A plate-shaped take-out portion 22b and a holding portion 2 extending in opposite directions.
2c into the outer electrode lead fitting 22. At this time, for example, a conductive paste containing powder of a heat-resistant metal such as platinum is applied to the element shoulder 20a.
If a small amount is applied between the outer surface of the lead fitting 22 and the inner surface of the lead fitting 22, electrical contact is ensured and durability is improved (not shown). Next, there is an element contacting part 23a made of a heat-resistant conductor such as heat-resistant steel, having a through hole 23c for introducing air, and having one end shaped so as to be in close contact with the inner surface of the opening of the element 20, and the contacting part 23a.
Insert the inner electrode lead fitting 23 into the opening of the element 20, which is made of a lead wire 23b made of heat-resistant steel or the like and which is held while ensuring conductivity by, for example, welding and extends in the opposite direction to the contact surface of the contact portion 23a. do. At this time, as described above, it is effective to apply a small amount of heat-resistant conductive paste between the inner surface of the element opening and the contact surface with the lead fitting 23. Furthermore, it is made of a heat-resistant insulating material, such as alumina, which has higher strength and thermal shock resistance than solid electrolytes and has a lower heat transfer coefficient than graphite, etc., and has an outer diameter slightly smaller than the outermost wall of the element 20. The inner insulating tube 24 has a cylindrical shape with a through hole 24a for introducing air in the center, and the lead wire 23b of the inner electrode lead fitting 23 is inserted into the through hole 24a to form the outer electrode lead. The metal fitting 22 is assembled so as to be sandwiched between the take-out part 22b and the holding part 22c.
The aforementioned structure is made of the same type of heat-resistant insulating material as the inner insulating tube 24, has a shoulder portion 21a for fixing to the housing, and has a diameter slightly larger than the outer diameter of the cylindrical portion of the outer electrode lead fitting 22. The outer insulating tube 2 has a through hole in which an element locking part 21b with a small diameter is formed at the tip for locking the element 20.
1, and the element 20 is locked to the element locking part 21b of the outer insulating tube 21 via the outer electrode lead fitting 22. Next, the gap between the element 20 and the outer insulating tube 21 is sealed using a heat-resistant sealing material 25 such as glass, and the gap between the outer insulating tube 21 and the inner insulating tube 24 is filled with a heat-resistant adhesive 26. After the device is fixed, a device protection cover 2 made of heat-resistant steel etc.
7a into the housing 27 and fixed using the protective cover 28, heat-resistant cushion material 29, and protective cover positioning ring 30. In this state, the extraction part 22b of the outer electrode lead fitting 22
and the upper end of the protective cover 28 are joined by welding or the like while ensuring conductivity, and then the lead wire 23b of the inner electrode lead fitting 23 and the covered wire 32 are connected.
are connected by a terminal 31, and the covered wire 23 is fixed by a rear protective cover 33 and a heat-resistant elastic body 34. Although an improved oxygen sensor is thus completed, this oxygen sensor also has the following drawbacks.

(a) Since the through hole 24a of the inner insulating tube 24 is provided for introducing air, it needs to have a considerably larger inner diameter than the wire diameter of the lead wire 23b of the inner electrode lead fitting 23. Therefore, since the lead wire 23b is supported by the joint with the inner electrode lead fitting 23 and the terminal 31, both ends of the lead wire may be damaged by the vibrations generated when the vehicle is mounted on an exhaust pipe and driven. Repeated stress is generated, and problems may occur such as when the joint between the lead wire 23b and the inner electrode lead fitting 23 comes off, or when the joint between the terminal 31 and the lead wire 23b comes off.

(b) Due to the same cause as (a), the amplitude of the covered wire 32 becomes large, and the heat-resistant elastic body 34 that fixes the covered wire 32 to the rear protective cover 33 is destroyed, or the covered wire 32 and the terminal The joint with 31 becomes loose and comes off.

The present invention is intended to solve the conventional drawbacks,
It is an object of the present invention to provide a structure with high vibration resistance regarding potential extraction from an inner electrode layer of an oxygen sensor element.

The oxygen sensor of the present invention is an oxygen sensor in which an element having inner and outer electrode layers formed on the inner and outer surfaces of a solid electrolyte container is fixed to the tip of an insulating tube fixed by a housing. an element contact part made of a heat-resistant conductive material molded so as to come into contact with the insulating tube, and a tubular body made of a heat-resistant conductive material fitted into the insulating tube and having one end secured to the element contact part to ensure electrical continuity. It is characterized in that an output extraction part for the inner electrode is attached, which comprises an output extraction part that abuts or joins and has a hole or groove penetrating the inner and outer surfaces of the tubular body near the other end.

The present invention will be explained below based on examples.

FIG. 4 is a sectional view of one embodiment of the present invention, and FIG. 5 is a perspective view showing the main structure of the embodiment of FIG. 4. As shown in the figure, first, the element 20 made of the solid electrolyte container described above is attached to the outer electrode lead fitting 22.
Insert into. Next, an element contact surface 231b is formed of a heat-resistant conductor such as heat-resistant steel, has a through hole 231a for introducing air, and has a shape that fits closely at least a part of the inner surface of the opening of the element 20 at one end. The element contacting part 231 is inserted into the opening of the element 20, and a tubular part 232b, which is made of the same kind of material and has a tubular shape with an outer diameter smaller than the outermost diameter of the element 20, is placed on the element contacting part 231. , the tubular portion 232b
The contact portion 2 is shaped so that one end thereof can contact the end surface of the front element contact part 231 opposite to the element contact surface 231b, and the through hole inside the tube is not closed.
32a and the contact portion 232a of the tubular portion 232b.
A lead component (output extraction component) 232 having an air introduction hole 232c penetrating from the outer surface to the inner surface of the tube is placed near the end on the opposite side. At this time, the inner surface of the opening of the element 20 and the element contact part 23
Powder of a highly heat-resistant metal such as platinum is contained between the element contact surface 231b of the lead component 231 and the end surface opposite to the element contact surface 231b of the element contact component 231 and the contact portion 232a of the lead component 232, respectively. Applying a small amount of conductive paste ensures electrical contact and improves durability (not shown). Next, the lead component is made of a heat-resistant insulating material that has higher strength and thermal shock resistance than a solid electrolyte and has a lower heat transfer coefficient than a metal material, and has an outer diameter slightly larger than the outermost diameter of the element 20. An inner insulating tube 241 having a through hole 241a having an inner diameter slightly larger than the outer diameter of the tubular portion 232b of the lead component 232 is assembled so that the tubular portion 232b of the lead component 232 is inserted into the through hole 241a.
Inserting such a structure into the aforementioned outer insulating tube 21,
The gap between the outer insulating tube 21 and the element 20 is sealed with a heat-resistant sealing material 25 such as glass, and the gap between the outer insulating tube 21 and the inner insulating tube 241 is filled with a heat-resistant adhesive 26 and fixed. Thus element 20
is fixed to the tip of the outer insulating tube 21, and the lead component 232 is also fixed to the inner insulating tube 241 while maintaining electrical continuity with the inner electrode layer 20b of the element 20 via the element contacting component 231. At this time, if the above-mentioned heat-resistant adhesive is filled into the gap between the tubular portion 232b of the lead component 232 and the through hole 241a of the inner insulating tube 241, the lead component 232 is fixed even more firmly. In this state, the element protection cover 27a is inserted into the housing 27 made of heat-resistant steel or the like with the element protection cover 27a at the lower end, and the protection cover 28, heat-resistant cushion material 29, and protection cover positioning ring 30 are inserted.
The end of the take-out part 22b of the outer electrode lead fitting 22 and the upper end of the protective cover 28 are joined by welding or the like while ensuring conductivity, and the end of the tubular part 232b of the lead part 232 is fixed. coated wire 3
The two core wires are exposed and inserted and bonded together by crimping or the like while ensuring conductivity, and then the covered wire 32 is fixed with a rear protective cover 33 and a heat-resistant elastic body 34. Thus, the oxygen sensor according to the present invention was completed.
The potential of the inner electrode layer 20b of the element 20 is transmitted from the inner surface of the element 20 near the opening to the covered wire 32 via the element contact part 231 and the lead part 232,
On the other hand, the air that is the internal standard substance that has flowed into the protective cover flows into the lead component from the air introduction hole 232c of the lead component 232, and reaches the inner surface of the element 20 through the through hole 231a of the element contact component 231.

The above embodiment of the present invention has an element contact part (element contact part 231) and an output extraction part (lead part 23).
2) are clearly separated, and the two are brought into contact when assembling the oxygen sensor.
Other embodiments of the present invention having such a structure are shown in FIGS. 6 to 9. Figure 6 shows the element contact part 231.
This is an example in which the joint between the upper end and the contact portion 232a of the lead component 232 is tapered, and FIG. 7 is an example in which the shape of the opening of the element 20 is not tapered and the shape of the element contact component 231 is changed. shows. In the present invention, if necessary, the element contact part 231 and the lead part 232 may be joined in advance by welding or the like as shown in FIG. Lead parts 23
Even if the second air introduction hole 232c is shaped like a slit perpendicular to the axis as shown in FIG. 9, the effect of the present invention will not change.

Of course, the output extraction part for the inner electrode of the present invention may be formed integrally with the element contact part and the output extraction part, instead of having to be separate parts as in the above embodiments. In this case, the tubular body may be joined to the contact part made of heat-resistant steel or the like by welding or the like, or the tip of the tubular body may be processed to form the contact part.
A concrete example of this is shown in FIGS. 10 and 11. In the figures, the same symbols represent the same meanings as in FIGS. 4 and 5.

As shown in FIG. 12, an example of integrating the element contacting part and the output extraction part is to change the molding method of the element contacting surface 231b of the inner electrode lead fitting 231, so that the outer peripheral surface is connected to the element 20. They may be in contact with each other, and even if the inner surface shape of the element 20 near the opening is different, for example, the shape of the element contact surface 231b may be matched as shown in FIG. 13. Furthermore, as shown in FIGS. 14A and 14B, the element contacting surface 231b of the inner electrode lead fitting 231 does not need to exist around the entire circumference of the end, and even if a portion is cut out, the effect of the present invention will not change. .

In the oxygen sensor of the present invention, as described above, the tubular output extraction part of the output extraction part (lead part) for the inner electrode is fitted and fixed in the insulating tube, so that disconnection due to vibration can be completely prevented. Furthermore, since the take-out part is fixed as described above, the amplitude of the covered wire connected thereto is also reduced, damage to the heat-resistant elastic body can be prevented, and loosening of the joint between the covered wire and the lead component can be prevented. Furthermore, by using the inner electrode extraction part of the present invention, there is an advantage that the ease of assembling the oxygen sensor is improved and the cost can be reduced.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a conventional oxygen sensor, Fig. 2 is a cross-sectional view of an improved oxygen sensor, Fig. 3 is an exploded perspective view showing the main components of the oxygen sensor shown in Fig. 2, and Fig. 4 is a cross-sectional view of a conventional oxygen sensor. A sectional view of one embodiment of the invention, FIG.
An exploded perspective view showing the main components of the embodiment shown in the figure;
6 to 9 are views showing other embodiments of the present invention, FIG. 10 is a sectional view of still another embodiment of the invention, and FIG. 11 is a main configuration of the embodiment of FIG. 10. Exploded perspective view, Figures 12 to 14 A, B
FIG. 3 is a diagram showing another embodiment of the present invention. In the figure, 1, 20...Element, 1b, 20b...Inner electrode layer, 2, 27...Housing, 21...Outer insulating tube, 22...Lead fitting for outer electrode, 24
...Inner insulating tube, 32...Electrified wire, 231...Element contact parts/inner electrode lead fitting, 232...
lead parts.

Claims (1)

[Claims] 1. In an oxygen sensor consisting of an element having inner and outer electrode layers formed on the inner and outer surfaces of a solid electrolyte container fixed to the tip of an insulating tube fixed by a housing, one end of the element is in contact with at least a part of the inner surface of the opening of the element. The formed element contact portion made of a heat-resistant conductive material and a tubular body made of a heat-resistant conductive material are fitted into the insulating tube and one end is brought into contact with or joined to the element contact portion to ensure electrical continuity. An oxygen sensor characterized in that an output extraction part for an inner electrode is attached near the other end, and an output extraction part formed by providing a hole or groove penetrating the inner and outer surfaces of a tubular body.