JPS6335404Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an oxygen sensor having a waterproof structure for protecting a sensor element.

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 electrolyte 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 2 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 conductive stem 5 made of, for example, graphite is inserted into the gap between the inner surface of the element opening and the stem 5. Material 6
is filled. 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 coiled spring 11 made of a heat-resistant elastic and conductive material such as heat-resistant steel is installed between the terminal 10 and the stem 5, and connects the inner surface near the opening of the element 1, the conductive material 6, and the conductive material. At the same time as ensuring contact between the material 6 and the stem 5, the shape of the conductor 6 is maintained so that it does not collapse due to vibration etc., and the potential generated in the inner electrode layer 1b of the element 1 is transferred to the vicinity of the opening of the element 1. is transmitted from the inner surface of the terminal 10 via the conductor 6, stem 5, and spring 11. However, the conventional oxygen sensor having such a structure has the following drawbacks.

1 Heat-resistant conductors such as graphite do not have sufficient heat resistance, so mounting positions are limited, and if a certain amount of protrusion is to be ensured, the element itself must be made larger.

2 Graphite etc. often have a high heat transfer rate, so when driving with an oxygen sensor attached to the exhaust pipe of a car,
When water hits the exposed portion (upper half), the temperature drop due to the water 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, an oxygen sensor was previously proposed in which a sensor element was attached to the tip of an insulating tube made of ceramic or the like, and the insulating tube was locked and fixed to a housing.

Details of this improved oxygen sensor will be explained with reference to FIGS. 2 and 3.

That is, the shoulder portion 20a is made of an oxygen ion conductive material such as zirconia stabilized with yttrium oxide or the like, and the outer diameter near the opening is larger than the tip.
The inner and outer electrode layers 20b and 20c made of platinum-based 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). The element 20 is made of a heat-resistant conductive material such as heat-resistant steel and has a cylindrical part having an inner diameter slightly larger than the outermost circumferential diameter of the element. an element contacting part 22a consisting of a tapered part that is smaller than the outer circumferential diameter and larger than the outer diameter of the tip of the element and has a shape corresponding to the shoulder part 20a of the element 20; It is inserted into the outer electrode lead fitting 22, which consists of a plate-shaped take-out part 22b and a holding part 22c, which extend in the opposite direction. At this time, a conductive paste containing powder of a heat-resistant metal such as platinum is applied to the element shoulder 2.
If a small amount is applied between the outer surface of Oa and the inner surface of lead metal fitting 22, electrical contact will be ensured and durability will also be improved (not shown). Next, an element contact portion 23a is formed of a tube made of a heat-resistant conductor such as heat-resistant steel, and the inner surface of the tube is bent outward at one end to contact the inner surface of the element 20 near the opening. Part 2
3a, and an air introduction hole 23c penetrating from the outer peripheral surface toward the inner peripheral surface near the end of the tubular part 23b opposite to the element contacting part 23b. 23 is placed so that the element contact portion 23a contacts the inner surface of the opening of the element 20. At this time, as described above, it is effective to apply a small amount of heat-resistant conductive paste between the element contact portion 23a and the inner surface of the opening of the element 20. Next, 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 metal materials, and has an outer diameter slightly smaller than the outermost diameter of the element. Then, a cylindrical inner insulating tube 24 having a through hole 24a with an inner diameter slightly larger than the outer diameter of the tubular part 23b of the inner electrode lead fitting 23 is inserted into the through hole 24a. Combine by inserting. In this state, a tube is made of the same material as the inner insulating tube 24, has a shoulder portion 21a for fixing to the housing, has an inner diameter slightly larger than the outer diameter of the cylindrical portion of the outer electrode lead fitting 22, and has the element 20 at its tip. The element 20 is inserted into an outer insulating tube 21 having a through hole in which an element locking part 21b with a small diameter is formed for locking, and the element 20 is inserted through an outer electrode lead fitting 22.
is locked to the element locking portion 21b of the outer insulating tube 21. 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 then the gap between the outer insulating tube 21 and the inner insulating tube 24 is filled with a heat-resistant adhesive 26 and fixed. After tightening, it is inserted into a housing 27 made of heat-resistant steel, etc., which has an element protection cover 27a at the lower end, and the protection cover 28,
It is fixed using a heat-resistant cushion material 29 and a protective cover positioning ring 30. Next, the end of 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 upper end of the tubular part of the inner electrode lead fitting 23 is coated. After the core wire of the wire 32 is exposed and inserted and bonded by crimping or the like, the covered wire 32 is fixed with the rear protective cover 33 and the heat-resistant elastic body 34.
The improved oxygen sensor is thus completed. This improved oxygen sensor eliminates the drawbacks of conventional oxygen sensors, makes it possible to downsize the element while maintaining a certain amount of protrusion, and reduces the temperature drop transmitted through the housing even when water is splashed onto it. Element cracking can also be prevented.

However, even in such an improved oxygen sensor, when a large amount of water comes flying into the exposed part, air flows in through the slit 33a at the lower end of the rear protective tube 33 and the recess 28a at the upper end of the protective tube 28. Water infiltrates from the channel and further travels inside the inner electrode lead fitting 23 through the air introduction hole 23c of the inner electrode lead fitting 23, and then reaches the element 2 at the tip.
0, and if the element 20 is in a high temperature state at this time, it has the disadvantage that the element 20 will be destroyed.

Even if a large amount of water splashes onto the exposed part, this design prevents the water from reaching the tip of the element through the air introduction path, and at the same time prevents air, which is a standard substance, from flowing into the inside of the element. An object of the present invention is to provide an oxygen sensor having a structure.

In the oxygen sensor of the present invention, an element having electrodes 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 so that the entire element is located within the gas to be measured. It is characterized in that the tube is provided with an air introduction hole connecting the rear end portion and the inner surface of the element, and a heat-resistant porous filter is attached to at least a portion of the air introduction hole.

Hereinafter, the present invention will be specifically explained based on examples.

As shown in FIGS. 4 and 5, the element 20 made of the aforementioned solid electrolyte is inserted into the aforementioned outer electrode lead metal fitting 22, and the element 20 made of a heat-resistant conductor such as heat-resistant steel is connected to the inner surface of the tube at one end. An element contact part 231a that is bent outward and formed to contact the inner surface near the opening of the element 20, a tubular part 231b that extends continuously from the contact part 231a, and the tubular part 231b.
an air introduction hole 231c penetrating from the outer circumferential surface to the inner circumferential surface near the end opposite to the element contact portion 231a;
The inner electrode lead fitting 231, which has a constricted pipe part 231e provided at an appropriate position near the center of the tubular part 231c, is made of a material with good high heat oxidation resistance, such as a wire mesh made of heat-resistant steel wire, for air circulation. A flexible filter 232 is connected to the air introduction hole 231.
The structure filled in the upper half of the tubular portion 231b from the end on the side where c is located is placed so that the element contact portion 231a contacts the inner surface of the element 20 near the opening. At this time, the filter 232 is prevented from falling into the inside of the element 20 by the tube contraction part 231e of the inner electrode lead fitting 231. Further, as described above, it is effective to apply a small amount of heat-resistant conductive paste to the element contact portion 231a and the inner surface of the opening of the element 20. Next, the above-mentioned inner insulating tube 24
After combining, the whole is inserted into the through hole of the outer insulating tube 21, the gap between the element 20 and the outer insulating tube 21 is sealed with a heat-resistant sealing material such as glass, and the outer insulating tube 21 and the inner insulating tube are 24 and the tubular portion 2 of the inner insulating tube 24 and the inner electrode lead fitting 231
A heat-resistant adhesive is filled in each gap with 31b and fixed. In this state, the protective cover 28, heat-resistant cushion material 29, protective cover positioning ring 30, etc. are used to fix the protective cover 28, heat-resistant cushion material 29, protective cover positioning ring 30, etc. to a housing made of heat-resistant steel or the like and having the element protective cover 27a at the lower end, and the outer electrode lead fitting 22 is fixed. The end of the extraction portion 22b and the upper end of the protective cover 28 are joined by welding or the like while ensuring conductivity. On the other hand, the covered wire 32 is inserted into the end of the tubular part 231b of the inner electrode lead fitting 231 with the core wire at the tip exposed, and after being connected by crimping or the like, the covered wire 32 is connected to the rear protective cover 33 and the heat-resistant elastic body 34. Make it more fixed. At this time, protective cover 2
The air inflow path 3 is formed by a dent or notch in the upper end of the 8 and a part of the part that overlaps with the rear protective cover 33.
Set 5. Even if water were to infiltrate from the air inflow path 35 and into the inside of the inner electrode lead fitting 231 through the air introduction hole 231c, the flow of water would be blocked by the filter 232 and the element 20 would be heated to a high temperature. In other words, when the temperature of the filter 232 is also high, liquid water vaporizes while passing through the filter 232 and does not reach the tip of the element while remaining in liquid form.

Other embodiments of the invention are shown in FIGS. 6-9. In the present invention, when the shape of the element contacting part 231a of the inner electrode lead fitting 231 is changed as shown in FIG. 6, and as shown in FIG. They can be applied even if the situation is different. Furthermore, as shown in FIG. 8, a conductive heat-resistant filter 232a may be used instead of the element contact portion 231a.
Even if the entire lead metal fitting for the inner electrode is replaced with the filter 232b made of the same material as described above, the effects of the present invention can be obtained in the same manner as in the above embodiment.

As mentioned above, heat-resistant steel wire is most suitable for the filter used in the present invention, but any other heat-resistant and corrosion-resistant material can be used, such as carbon fiber, ceramic fiber, glass fiber, etc. These may be inserted into the tubular part in an amorphous state, or may be formed into a predetermined shape in advance.

The present invention has the effect that the oxygen sensor element can be reliably protected from damage caused by water by simply inserting a heat-resistant filter into a part of the air introduction hole.

[Brief explanation of the drawing]

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 a perspective view showing the main components of Fig. 2, and Fig. 4 is a cross-sectional view of an improved oxygen sensor. FIG. 5 is a perspective view of the inner electrode lead fitting of the present invention, and FIGS. 6 to 9 are cross-sectional views of main parts of other embodiments of the present invention. In the figure, 1, 20... Element, 2, 27... Housing, 21... Outer insulating tube, 22... Lead fitting for outer electrode, 23, 231... Lead fitting for inner electrode, 231e... Condensed tube part , 232...filter, 24...inner insulating tube.

Claims (1)

[Scope of utility model registration request] An element having electrodes formed on the inner and outer surfaces of the solid electrolyte container is fixed and fixed to the tip of an insulating tube fixed by a housing so that the entire element is located within the gas to be measured, and the rear end and the rear end are attached to the insulating tube. An oxygen sensor comprising: an air introduction hole connected to an inner surface of an element; and a heat-resistant porous filter attached to at least a part of the air introduction hole.