JPS6334980B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention improves low-temperature operability, prevents element cracking, and ensures reliable output by improving the assembly structure of the oxygen sensor element and the housing as well as the extraction structure of the inner and outer electrodes. This invention relates to an oxygen sensor that can be taken out.

An oxygen sensor is a solid electrolyte container (sensor element) in which inner and outer electrode layers made of platinum-based metal 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. For example, using air containing a certain amount of oxygen, such as air, as an internal standard substance, the ratio of the equilibrium oxygen partial pressure between the internal standard substance that contacts the inner and outer electrodes of this sensor element and the gas to be measured is calculated. It converts into a potential difference and detects the oxygen concentration of the gas to be measured. In automobiles, this oxygen sensor plays the role of detecting the oxygen concentration in exhaust gas that is fed back to the air-fuel ratio control mechanism of the engine, and is indispensable for exhaust gas purification systems using three-way catalysts.

There are two types of oxygen sensors: the so-called air electrode oxygen sensor, which uses atmospheric oxygen as the standard oxygen partial pressure, and the solid-state electrode oxygen sensor, which uses the equilibrium oxygen partial pressure of a metal and its oxide. Although there are two types, conventional oxygen sensors that use air as an internal standard usually have a structure as shown in FIG.

For example, an element protection cover 3 is inserted into a housing 2 made of a heat-resistant metal such as heat-resistant steel, and an element 1 having inner and outer electrode layers 1b and 1c formed on the inner and outer surfaces of a solid electrolyte container is inserted thereon. This element 1 has the outer side of the tip in contact with the gas to be measured, the inner side of the tip in contact with air, which is an internal standard substance, and serves to separate the gas to be measured and air from mixing.
A shoulder portion 1a for fixing to the housing 2 is formed, and the inner and outer electrode layers are separated and insulated at the outer surface or opening end surface above the shoulder portion 1a. In the gap between the housing 2 and the element 1,
A seal ring 4 made of a heat-resistant conductor such as graphite is filled. This seal ring 4 prevents the gas to be measured from leaking from the gap between the housing 2 and the element 1, and at the same time prevents the electric potential of the outer electrode layer of the potential difference between the inner and outer electrode layers induced by the oxygen concentration of the gas to be measured into the housing. It plays the role of communicating to 2. A cushion ring 5 made of a heat-resistant material such as talc or asbestos is placed on the seal ring 4, and an annular presser plate 6 is placed on the cushion ring 5. on the other hand,
Inside the opening of the element 1, a conductive ring 11 made of the same material as the seal ring 4 and an internal terminal 12 made of heat-resistant steel and having a through hole for air conduction in the center are inserted. A coiled spring 13 is placed on this internal terminal 12.
The external terminal 10 is fixed to the upper end via a terminal holder 9 made of an insulator, and an air conductor is placed near the upper end. A rear protective tube 7 having a hole 7a is placed, and a positioning ring 8 for the rear protective tube is inserted into the gap between the rear protective tube 7 and the housing 2. In the above-described state, if the upper end 2a of the housing 2 is caulked by an appropriate amount over the entire circumference, the element 1 is fixed to the housing 2, and the potential of the outer electrode layer is applied to the shoulder of the element 1. 1a surface to the housing 2 via the conductive seal ring 4.
The potential of the inner electrode layer is transferred to the conductive ring 1
1. Internal terminal 12, external terminal 1 via spring 13
0, a potential difference is generated between the housing 2 and the external terminal 10, and the oxygen concentration in the gas to be measured can be detected. In this way, an oxygen sensor using air as the internal standard substance is completed.

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.
The heat-resistant conductor, such as graphite, which also serves as a sealing material, does not have sufficient heat resistance, so 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. If the element is large, the upper end is in contact with the outside air, so it takes time to reach the minimum operating temperature at which the element starts operating from a low temperature state. Especially when the measured gas temperature is low, it may take a long time to reach the minimum operating temperature. sea bream.

(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 (upper half), the temperature caused by the water will drop. The drop is immediately transmitted to the element via the housing conductive ring. If such a situation occurs when the element is in a high temperature state, the element made of a material such as zirconia, which is susceptible to thermal shock, will be destroyed.

(3) Furthermore, when caulking the upper end of the housing, due to the structure of the oxygen sensor, the caulking force applied to the upper end of the housing is directly applied to the element, so the caulking work must be performed with extreme caution. The element is destroyed.

The present invention is intended to solve the above drawbacks,
Shortens the time it takes for the element to reach the minimum operating temperature from a low temperature state, prevents element cracking even if water adheres to exposed parts during operation, and minimizes element breakage during assembly. The purpose of this invention is to provide an oxygen sensor that can

That is, the oxygen sensor of the present invention has an outer electrode made of a thin plate of a heat-resistant conductor and shaped to fit on the outer periphery of the sensor element on the opening side of the sensor element, which has inner and outer electrodes formed on the inner and outer surfaces of the solid electrolyte container. The lead fitting is electrically connected to and fitted to the outer electrode, and the sensor element is brought into contact with the inner periphery of the tip of the outer insulating tube with the outer periphery of the sensor element on the opening side, or via the outer electrode lead fitting. the inner periphery of the opening of the sensor element and the outer periphery of the cylindrical inner electrode lead fitting in contact with the inner periphery of the inner electrode,
An inner insulating tube having an air introduction hole in the center is inserted into the outer insulating tube, an output lead wire is connected to the outer and inner electrode lead fittings, and the outer insulating tube is made to protrude from the outer periphery of the tube. It is characterized by being locked and fixed to the housing at the shoulder.

In the present invention, the sensor element is constructed in the same manner as the conventional sensor element, except that it has a small shape that is about the size of the part used for measuring the tip of the conventional element. That is, the solid electrolytic container is made of an oxygen ion conductive ceramic material such as zirconia stabilized with yttrium oxide, which has been conventionally used for this type of purpose. The shape of the container is a cylindrical body with one end closed, and the outer periphery near the opening side has a large diameter, and a shoulder is provided so that the container is secured to the inner periphery of the tip of the insulating tube.

The present invention replaces the parts of conventional elements that are not used for measurement with insulating tubes, and this insulating tube has superior mechanical strength and thermal shock resistance compared to solid electrolytes such as alumina, and has better thermal shock resistance than metal materials. A tubular body made of an insulating material with low thermal conductivity is used.

In the present invention, since an insulated tube with low thermal conductivity is used as described above, the output lead wire must be heat resistant. Therefore, the present invention is characterized in that an oxygen sensor in which an element is locked and fixed to the tip of an insulating tube uses lead fittings for inner and outer electrodes for extracting output from the inner and outer electrode layers of the element. Although the present invention relates to an oxygen sensor using air as an internal standard substance, the output extraction means using the lead fittings for the inner and outer electrodes can also be applied to a solid polar oxygen sensor as is.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a sectional view of the oxygen sensor of the present invention, FIG. 3 is an enlarged sectional view of essential parts of the oxygen sensor, and FIG. 4 is an exploded perspective view showing the assembly of the sensor element.

When assembling the oxygen sensor, first, it is made of an oxygen ion conductive material, has a container shape with an outer diameter near the opening larger than the outer diameter of the tip, and has a shoulder 14a formed thereon. Element 14 with inner and outer electrode layers 14b and 14c formed of platinum-based alloy thin films
is made of a thin plate of a heat-resistant conductor such as heat-resistant steel, and has a substantially cylindrical element contact part 15a that fits into the shoulder part 14a of the element 14, and a part of the cylindrical shape extends in the opposite direction to the tip of the element. It is inserted into the outer electrode lead fitting 15 consisting of a shaped middle part 15b. In addition,
A lead portion 15c is connected to the tip of the intermediate portion 15b by welding or the like. In addition, for joining the element 14 and the lead metal fittings 15, a conductive paste containing powder of a heat-resistant metal such as platinum is applied to the element shoulder portion 15.
If a small amount is applied between the outer surface of the lead fitting 4a and the inner surface of the lead fitting 15, electrical contact is ensured and durability is further improved.

Next, a lead for the inner electrode is made of a heat-resistant conductor such as heat-resistant steel, has an air introduction hole 16a, has a shape such that its tip fits closely to the inner periphery of the opening of the element 14, and is connected to a lead wire 16b by welding or the like. Insert the metal fitting 16 into the opening of the element 14. 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 lead fitting 16 at this time.

Furthermore, an inner insulating tube 19 has a cylindrical shape with an outer diameter that is the same as or slightly smaller than the outermost diameter of the element 14, and has an air introduction hole 19a in the center and a lead wire extraction groove 19b in the axial direction on the outer periphery. are assembled by inserting the lead wire 16b of the inner electrode lead fitting 16 into the air introduction hole 19a and inserting the lead portion 15c of the outer electrode lead fitting 15 into the lead wire extraction groove 19b.

A shoulder portion 1 for fixing the element 14, outer and inner electrode lead fittings 15, 16, and inner insulating tube 19 to the housing in a combined state as described above.
8a, and has a through hole with a diameter slightly larger than the outer diameter of the outer electrode lead fitting 15, and an element locking part 18b with a smaller diameter for locking the element 14 at the tip. The element 14 is inserted into the tube 18 and is locked to the element locking part 18b of the outer insulating tube 18 via the outer electrode lead fitting 15.

At this time, heat-resistant sealing material 2 such as glass, etc.
0 is attached to the inner surface of the element locking part 18b of the outer insulating tube 18, and while maintaining contact between the outer electrode layer and the outer electrode lead fitting 15 at the shoulder part 14a of the element 14, it is heated by heat treatment etc. The heat-resistant sealing material is melted and sealed to prevent the gas to be measured from entering the inside of the outer insulating tube 18. Meanwhile, a heat-resistant adhesive 20a is filled into the gap between the outer insulating tube 18 and the inner insulating tube 19 while maintaining contact between the inner electrode lead fitting 16 and the inner electrode layer near the opening of the element 14. . Thus, the element 14 is fixed by the outer insulating tube 18 and the inner insulating tube 19,
The potential of the outer electrode layer is determined by the outer electrode lead fitting 15.
The potential of the inner electrode layer is taken out by the lead part 15c via the element contact part 15a and the intermediate part 15b, and the potential of the inner electrode layer is taken out by the lead wire 16 of the inner electrode lead fitting 16.
It can be taken out by b. In addition, the air serving as the standard substance is
a. Air introduction hole 16 of inner electrode lead fitting 16
A is introduced into the inside of the element 14, and at the same time is separated from the gas to be measured by the heat-resistant sealing material 20, so that a constant standard oxygen partial pressure can be maintained.
Element 14 outer electrode lead fitting 1 as described above
5. Inner electrode lead fitting 16, outer insulating tube 18
The structure consisting of the inner insulating tube 19 and the like is inserted into the housing 23 which has the inner and outer protective covers 21 and 22 at the lower end, and is made of heat-resistant steel and has a notch or recess 24a at the upper end for introducing air. The protective cover 24 held in place is placed, a cushion material 25 made of a heat-resistant material such as talc or asbestos is filled in the gap between the protective cover 24 and the housing 23, and a protective cover positioning ring 26 is placed on the cushion material 25. Place it. In this state, if the upper end 3a of the housing 23 is caulked by an appropriate amount over the entire circumference, the outer insulating tube 18 will be attached to the housing 2.
3, and thus the element 14 is also fixed. In this case, the element 14 is formed so as to be located inside the inner and outer element protection covers 21 and 22 and outside the housing 23. Furthermore, the lead portion 15 of the outer electrode lead fitting 15
c and the lead wire 16 of the inner electrode lead fitting 16
b are connected to the coated wire 29 by terminals 27 and 28, respectively, and then a rear protective cover 30 made of heat-resistant steel and having an air introduction slit 30a at the lower end is inserted into the notch or recess 24a of the protective cover 24.
and the slit 30a of the rear protective cover 30, fit together, and hold by welding, caulking, or the like. At this time, it is preferable to prevent a short circuit between the lead wires or between the lead wires and the protective cover using the terminal protection tube 32 made of a heat-resistant insulating material. After that, the gap between the upper end 30b of the rear protective cover 30 and the covered wire 29 is filled with a heat-resistant elastic body 31 such as silicone rubber, and the upper end 30b of the rear protective cover 30 is caulked in the radial direction. Covered wire 29
is fixed to the rear protective cover 30.

The oxygen sensor of the present invention is thus completed, and the standard substance, air, is passed through the slit 3 of the rear protective cover 30.
0a and a notch or dent 24 in the protective cover 24
a, the air introduction hole 19a of the inner insulating tube 19, and the inner electrode lead fitting 1.
When the air flows into the element 14 through the air introduction holes 16a of No. 6 and flows out, the heat-resistant sealing material 20 prevents the gas from mixing with the gas to be measured. Further, the potential of the outer electrode 14c of the element 14 is
From the element contacting part 15a of the outer electrode lead fitting 15 that contacts the outer surface of the shoulder part 14a of No. 4 to the intermediate part 15
b, the potential of the inner electrode 14b is transmitted to the coated wire 29 via the lead portion 15c and the terminal 27, and the potential of the inner electrode 14b is transmitted to the coated wire via the inner electrode lead fitting 16 which is in contact with the inner surface of the opening of the element 14, the lead wire 16a and the terminal 28. 29, which functions as an oxygen sensor.

Further, as shown in FIG. 5, when fixing the element 14 to the inner and outer insulating tubes 18 and 19,
4a and the locking portion 18b of the outer insulating tube 18,
They may be combined in a stepped shape.Furthermore, if it is desired to transmit the potential of the outer electrode to the housing 23, the outer electrode lead fitting 15 may be eliminated and the outer insulating tube 18 near the element locking portion 18b may be combined. A metal thin film layer 18c is formed on the inner and outer surfaces from the shoulder portion 18a to the shoulder portion 18a.
is formed by metal paste baking, vapor deposition, plating, etc., and if the outer electrode layer of the shoulder part 14a of the element 14 is brought into contact with the element locking part 18b of the metal thin film layer 18c, the potential of the outer electrode layer 14c The shoulder portion 18a of the outer insulating tube 18 passes through the metal thin film layer 18c.
from the bottom surface of the outer element protection cover 22 to the housing 23 through the opening of the outer element protection cover 22.

In addition to the shape described in the above embodiments, the outer electrode lead metal fitting in the present invention may have the shape described in the above embodiments, or if the shoulder portion of the element 14 is not tapered as shown in FIG. The end face may have a reduced diameter, or a portion of the cylindrical portion may protrude inward to ensure contact as shown in FIG. Furthermore, as shown in FIG. 8, when the shoulder portion 14a of the element 14 has a tapered shape that widens downward at the upper end opening, the element contact portion 15a of the outer electrode lead fitting 15 is moved downward to match the tapered shape. The object of the present invention can also be achieved with a tapered shape that widens in the direction.

In the oxygen sensor of the present invention, a method for extracting the potential of the outer electrode by forming a platinum-based alloy thin film 18c on the outer surface of the outer insulating tube 18 as shown in FIG. 9 can be considered, but the thickness of the thin film Otherwise, electrical conductivity may be lost due to peeling etc. when exposed to engine exhaust gas for a long period of time, requiring the use of a large amount of expensive platinum, and furthermore, the potential of the outer electrode layer is not transmitted to the housing. Similar to the potential of the inner electrode layer, it has drawbacks such as difficulty in connection when it is desired to take out the potential using a covered wire.

In contrast to the above, according to the outer electrode lead fitting of the present invention, the complicated process for forming a conductive thin film can be omitted, there is no need to use an expensive platinum-based alloy, and moreover, it can be connected to a covered wire. It has the advantage of being easy to connect using external terminals. Note that these advantages can be similarly applied to the lead metal fitting for the inner electrode.

The test results regarding the low-temperature operability and prevention of element cracking of the oxygen sensor of the present invention are shown.

The test was conducted using the oxygen sensor according to the embodiment of the present invention having the structure shown in FIG. 2 and the conventional oxygen sensor having the structure shown in FIG. 1 as a comparative example. After steady operation, the engine was stopped and restarted after a certain period of time, and the temperature rise at the tip of the element was measured. The results are shown in FIG. In the figure, the engine restart point S is indicated by an arrow, the temperature curve of the oxygen sensor according to the embodiment of the present invention is indicated by symbol A, the comparative example is indicated by symbol B, the engine exhaust gas temperature curve is indicated by symbol C, and the control signal is generated. The point is represented by the symbol D. In an embodiment of the invention,
Compared to the comparative example, the temperature at the tip of the element rises faster and the control signal is generated earlier.

Immediately after the test was completed, when the engine and oxygen sensor were in a high temperature state, the exposed parts of each of the example and comparative example were poured with water and the oxygen sensor was disassembled. As a result, the conventional oxygen sensor (comparative example) Although cracks occurred in the element in the oxygen sensor of the present invention, there were no abnormalities, and it was determined that cracks in the element during running in puddles could be dealt with without special waterproofing measures.

In addition, in the oxygen sensor of the present invention, the caulking force during assembly is provided by the outer insulating tube with high breaking strength, and since the caulking force is not directly applied to the element, the failure rate during assembly is reduced compared to conventional oxygen sensors. Furthermore, since the element can be made smaller, the amount of solid electrolyte such as zirconia used can be reduced, which is also effective in terms of resource conservation.

Therefore, when using the oxygen sensor of the present invention, low-temperature operability can be improved while ensuring the same protrusion amount as the conventional one, and the problem of element cracking when running in puddles can be solved. Furthermore, it has many advantages, such as being able to reduce the incidence of defects due to element cracking during assembly.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a conventional oxygen sensor, Fig. 2 is a sectional view of an embodiment of the present invention, Fig. 3 is an enlarged sectional view of the main part of Fig. 2, and Fig. 4 is a sectional view of the basic part of the present invention. FIG. 5 is a sectional view of another embodiment of the present invention, FIGS. 6 to 8 are perspective views showing examples of lead fittings for outer electrodes, and FIG. 9 is a perspective view of an outer insulating tube. FIG. 10, a perspective view showing a state in which a platinum-based alloy thin film is provided on the surface, is a graph showing the temperature characteristics of the oxygen sensor of the present invention. In the figure, 1... element, 2... housing, 3...
Protective cover, 4... Sealing, 5... Cushion ring, 14... Element, 15... Lead fitting for outer electrode, 16... Lead fitting for inner electrode, 18
...Outer insulating tube, 19...Inner insulating tube, 23...
housing.

Claims (1)

[Claims] 1 On the outer periphery of the opening side of the sensor element, which has an inner electrode and an outer electrode formed on the inner and outer surfaces of the solid electrolyte container,
An outer electrode lead fitting made of a thin plate of heat-resistant conductor and shaped to fit on the outer periphery is brought into electrical contact with the outer electrode and fitted, and the sensor element is attached to the inner periphery of the tip of the outer insulating tube on the opening side of the sensor element. The outer periphery of the sensor element is brought into contact with the inner periphery of the sensor element, or the outer periphery of the cylindrical inner electrode lead fitting is brought into contact with the inner periphery of the opening of the sensor element, and the outer periphery of the cylindrical inner electrode lead fitting is brought into contact with the inner periphery of the opening of the sensor element. , inserting an inner insulating tube having an air introduction hole in the center into the outer insulating tube, connecting output lead wires to the outer and inner electrode lead fittings, and causing the outer insulating tube to protrude to the outer periphery of the tube; An oxygen sensor characterized by being locked and fixed to a housing with a formed shoulder.