JPS6199856A - Oxygen concentration detector - Google Patents

Abstract

PURPOSE:To maintain a detecting function stable over a long period of time by providing a heat resistant metallic protective cylinder which is like a bottomed cylinder and is provided with gas flow ports to the cylindrical wall to the outside periphery of a supporting cylinder for housing an element consisting of a disk-shaped oxygen ion conductive solid electrolyte. CONSTITUTION:The element 1 consisting of the disk-shaped solid electrolyte has a projecting part 1c at the center and is formed with porous platinum electrode films 1a, 1b on both sides. The element 1 is housed into the supporting cylinder 2 consisting of the cylindrical heat resistant metal narrowed at one end. Washers 30, 31 consisting of an annular noble metal are welded to the inside periphery in the small-diameter part of the cylinder 2. The washers 30, 31 and the electrodes 1a, 1b are press-welded to provide hermetic sealing and electrical conduction. The stainless steel protective cylinder 14 which is like the bottomed cylinder and is provided with the gas flow holes 14a to the cylindrical wall is provided to the outside periphery of the cylinder 2. Stable oxygen concentration detection is thus executed over a long period of time.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an oxygen concentration detector, and is particularly suitable for detecting the oxygen concentration in a gas whose flow velocity and temperature vary widely, such as automobile engine exhaust gas. The present invention relates to an oxygen concentration detector suitable for.

[Background of the invention]

Conventionally, many of these types of detectors have used so-called bag-tube shaped elements, but it has been difficult to reduce the price because the forming of the bag-shaped solid electrolyte electrodes, especially the inner electrodes, cannot be mass-produced. Problems were pointed out.

Therefore, a disk-shaped element and a plug structure were considered with the aim of improving the mass production of the element and reducing the cost.
In this issue, something like the one shown in Figure 5 is proposed. Fifth
In the figure, 1 is a disk-shaped element with a convex cross section, 30 and 3
1 is a precious metal washer, 42 is a long tubular inner holder, 4
8 is an outer holder in the shape of a circular tube with a bottom and has a ventilation hole 48bi on the bottom surface.

58 is an inner conductor connected to the inner holder 42 , 43 is an insulating tube sheathed to the inner holder 42 , and 44 is the inner holder 42
45 is a coiled spring; 52 is an outer cylinder welded to the opening side of the outer holder 48; 53 (l-1: a pedestal for the coiled spring);

This proposal is based on the idea that highly malleable precious metal washers 30 and 31 are placed at positions corresponding to the periphery of the electrodes formed on both sides of the disk-shaped element 1.
The inner holder 42 and the outer holder 48, which are heat-resistant metal tubes, are sandwiched between the end faces of the inner holder 42 and the outer holder 48, and are pressed together by the spring pressure of the coiled spring 45 to achieve electrical conductivity and airtight sealing. ``propensity'' 2 can be realized. Of course, by heating under pressure, the noble metal washers 30 and 31 are diffused and welded to the element electrodes and the inner and outer holders 42, resulting in good airtight sealing and electrical conductivity. Heat ratio points can be detected. However, according to practical running durability tests, it was observed that the airtightness and conductivity gradually deteriorated, and the output value decreased. The reason for this is that during practical driving, the exhaust temperature fluctuates to 1], and due to this fluctuation, the temperature of the conductive and hermetic sealing parts also fluctuates widely. It turned out that this was due to the difference in expansion and contraction between the two, which caused the peeling.

In addition, in the above-mentioned conventional technology, a dedicated grounding lead wire is drawn out to prevent noise from entering the output signal, and the desired effect is obtained. However, since at least one electrode is grounded, When operated as such, there was a problem that the polarity of the current applied was limited to only one direction.

[Purpose of the invention]

A first object of the present invention is to provide an oxygen concentration detector that can withstand long-term practical use.

A second object of the present invention is to provide an oxygen concentration detector that can be used as an oxygen pump with arbitrary polarity.

[Summary of the invention]

In order to achieve the above-mentioned first object, the present invention covers the support tube of the disk-shaped element, particularly the outer periphery of the conductive and hermetic sealing portion, with a bottomed cylindrical protective tube, and specifies the position of the gas flow port. By doing so, the structure is designed to greatly alleviate the influence of exhaust temperature,
In addition, in order to achieve the second purpose, one end of the support tube is coated with an insulating layer so that both electrodes of the element are ungrounded, and the exhaust pipe is hermetically sealed through this insulating coating. It is composed of

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to the drawings.

Figures 1 to 4 all show one embodiment of the present invention, with Figure 1 being a longitudinal cross-sectional view of the whole, Figure 2 being a vertical cross-sectional view in the axial direction of Figure 1, and Figure 3 showing an element. FIG. 4 is an enlarged view of portion A in FIG. 1.

In these figures, 1 is a disk-shaped element consisting of a disk-shaped solid electrolyte body with a protrusion IC in the center and porous platinum electrode films 1a and 1b formed on both sides, and 2 is a disk-shaped element with one end shaped like a trumpet. 3 is a ceramic heater tube having a large-diameter groove at one end, and has a current-carrying heat generating layer 3a made of a thick film of stainless steel inside; 4 is a ceramic heater tube with large-diameter grooves at both ends; This is a steatite lead holder that has four holes penetrating between both grooves, and has a stepped shoulder 4a at the other end of the outer periphery. 5 is a plate made of spring material, 6
is made of a silicone rubber material and has four through holes; 7 is a plug body with a hexagonal opposite side, a screw, and a ring-shaped groove 7a on the outer periphery and a stepped through hole; 8 is a plug with one end facing inward; It is an outer support tube made of stainless steel tube with the other end bent outward, and the surface of the other end is coated with an insulating film 8a which is densely formed with magnesia, alumina, and spinel powder by plasma spraying. 9 and 10 are brass ring-shaped knobs,
11 is a press-fit ring made of brass tube, 12 is an outer cylinder made of stainless steel tube having stepped parts 12a and 12b'l formed by binding the other end in two steps, and 13 is formed on one surface of element 1 by plasma spraying. A gas diffusion resistance film made of magnesia, alumina, and spinel; 14 is a bottomed cylindrical protection tube made of stainless steel plate with a plurality of flow holes 14a provided on the outer peripheral wall; 16 is a semi-cylindrical protection tube made of stainless steel plate; Inner terminal, 17, outer terminal made of stainless steel plate material, 18° 19.24
．． 25 is an intermediate lead made of nickel wire, 22, 23, and 28 are external leads made of nickel-plated copper stranded wire insulated with fluorine resin, and 20.21° and 26.27 are crimp connectors.

Each of the above parts is assembled in the following steps.

First, platinum washers 31 and 30 are welded to the inwardly bent portion of the outer support tube 8 and the expanded surface portion of the inner support tube 2, respectively. Next, one end of the inner terminal 16 is welded to the other end of the inner support tube 2, one end of the intermediate lead 18 is crimped with the other end 16a of this terminal 16, the intermediate lead 18 is twisted, and the other end is connected to the outer lead. A crimp connection is made with one end of 22 using a crimp connector 20.

Next, the outward bending of the outer support tube 8 is performed on the side inner wall of the insulating layer 8a.
One end of the outer terminal 17 is welded to the part where there is no outer terminal, and the intermediate lead 19 and the outer lead 23 are similarly crimped and connected. moreover,
At the other end of the ceramic heater tube 3, terminals 24a and 258, which are nickel-plated tungsten lead-out terminals, are provided.One end of the intermediate leads 24 and 25 is silver soldered to each, and the external lead 23 is connected in the same manner. and 28
Connect to. Furthermore, a gasket 9 is attached to the stepped portion A of the plug body 7.
After sequentially inserting the outward bent flange of the inner support tube 8 and the packing 10, and press-fitting the press-fit ring 11 tightly, the plug body 7 is inserted.
The other end 7C is partially caulked and fixed.

Thereafter, subassemblies such as the inner support cylinder 2 and the inner terminal 16 are inserted into the ceramic heater tube 3, and then...

The element 1 is housed at the end and inserted into the inwardly bent part of the outer support cylinder 8. Next, lead holder 4, disc spring 5, grommet 6
are sequentially extrapolated to the external leads 22, 23, 28°29.1.
Finally, the outer cylinder 12 is sheathed, and with the stepped parts 12a and 12b pressurized in the axial direction, the ring-shaped groove 7a of the stopper 7 is
Tighten inward at several points to fix. In this state, a gas diffusion resistance film 13 is placed on the central exposed surface of one electrode 1b of the element 1.
is formed, and then the protective tube 14 is welded to one end side 7b of the plug body 7 below the thread. In this way, the element 1 can be hermetically sealed and conductive, but by energizing the ceramic heater 3 and gradually increasing the temperature of the entire element accommodating part to about 800°C, the platinum washers 30 and 31 are crimped and sealed, respectively. It is uniformly diffused to the support cylinder side and the element side, and even better airtightness and conductivity can be obtained.

According to this structure, even if exposed to wide and rapid fluctuations in exhaust gas temperature during practical driving, the element portion can be kept at a substantially constant temperature by energizing the protection tube 14 and the ceramic heater 3. Therefore, stable detection function can be maintained over a long period of time.

In addition, since both electrodes of element 1 are ungrounded, only the stoichiometric air-fuel ratio point can be detected as an oxygen concentration battery.
'It can operate as an oxygen pump in any direction.
It is possible to detect air-fuel ratios over a wide range from high to lean.

〔Effect of the invention〕

As is clear from the above description, the present invention has the advantage of being able to maintain a stable detection function over a long period of time and being able to be used as an oxygen pump in any direction.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, FIG. 2 is a vertical sectional view in the axial direction of FIG. 1, FIG. 3 is a partially enlarged view of the vicinity of the element, and FIG. FIG. 5, which is an enlarged view of part A, is a vertical sectional view of the conventional device. DESCRIPTION OF SYMBOLS 1... Disk-shaped element, 2... Inner support cylinder, 3...
Ceramic heater tube, 8...Outer support tube, 8a...
Insulating film, 14...protective tube, 30.31...precious metal washer.

Claims (5)

[Claims] 1. An element made of a disk-shaped oxygen ion conductive solid electrolyte having porous thin film electrodes on both sides, a support tube made of a cylindrical heat-resistant metal with one end narrowed to accommodate the element, and an inner periphery of the small diameter part of the support tube. In the oxygen concentration detector, the oxygen concentration sensor includes a welded ring-shaped washer made of a noble metal, and is configured such that the washer and an electrode provided on one surface of the element are pressed together to perform airtight sealing and conductivity. An oxygen concentration detector characterized in that a protective cylinder made of heat-resistant metal is provided around the outer circumference of the cylinder in the shape of a cylinder with a bottom and a gas flow port in the cylinder wall. 2. The other end of the support tube is made into a wrapper shape, and at least the surface of the expanded portion thereof is covered with an electrically insulating layer, and is hermetically sealed to the pipe wall of the gas to be measured via the insulating layer, and a part of the support tube is The oxygen concentration detector according to claim 1, characterized in that the conductive member is drawn out further. 3. The electrode on the other side of the element is electrically connected to the expanded part of an internal support cylinder made of a tubular heat-resistant metal whose one end is expanded into a lap shape through a precious metal washer. An oxygen concentration detector according to claim 1. 4. 4. The oxygen concentration detector according to claim 3, wherein the expanded portion of the internal support tube is pressed against the element by a disk-shaped spring via a tubular heat-resistant insulating member. 5. 5. The oxygen concentration detector according to claim 4, wherein a conductive heating member is embedded in the element side of the tubular insulating member.