JP2822735B2 - Stacked oxygen concentration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stacked oxygen sensor, and more particularly to a stacked oxygen sensor having a sensor element provided with an annular metal holder.

[0002]

2. Description of the Related Art In a laminated oxygen sensor, for example, ceramic green sheets provided with electrodes as required are sequentially laminated on a suitable support, and then fired to form a detection layer, and a protective layer is provided on the surface of the detection layer as desired. The sensor element is manufactured by incorporating the sensor element into a predetermined casing and wiring. The shape of the sensor element is not particularly limited, but if it is flat (or prismatic), it can be easily formed by sequentially laminating ceramic green sheets on a flat substrate and then firing, so that production is easy and production is easy. High in nature. For this reason, a flat sensor element is usually used.

When a sensor element is incorporated in a casing, positioning of the sensor element and sealing between the sensor element and the casing are important. In particular, when the sensor element is flat and the casing is cylindrical (this shape is common), it is difficult to seal between the sensor element and the casing.

[0004] In order to facilitate the positioning of the sensor element, for example, Japanese Utility Model Publication No. 63-11644 discloses a stacked oxygen sensor in which a projection is provided on the sensor element.
Also, in order to sufficiently seal the gap between the sensor element and the casing, a projection made of the same material as the sensor element and having substantially the same outer diameter as the inner circumference of the casing is slip-cast on the outer periphery of the flat sensor element (casting method). Has been proposed.

[0005]

Problems to be Solved by the Invention
In the stacked oxygen sensor disclosed in Japanese Patent Application Laid-Open No. 4 (1999) -1995, the role of the projection is positioning, and the sealing between the sensor element and the casing is performed by the filler. Is bad. In addition, since the sealing property of the filler is not sufficient, the reliability of the stacked oxygen sensor is low.

A stacked oxygen sensor having a projection formed by slip casting has a sufficient sealing property between the sensor element and the casing. However, when baking after forming a cylindrical projection on the outer periphery of the flat sensor element, firing temperature, temperature distribution, and the like, in order to uniformly shrink the form having both the flat portion and the cylindrical projection, It is necessary to determine in advance the optimum conditions in terms of the element holding method and the like, and the productivity of the sensor element is low, which may impair the high productivity that is an advantage of the stacked oxygen sensor having the flat sensor element. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and has as its object to provide an excellent sealing property between a sensor element and a casing, easy production and high productivity, and An object of the present invention is to provide a stacked oxygen sensor having a high degree of freedom in designing a sensor element fixing portion.

[0008]

According to the present invention, there is provided a stacked oxygen concentration sensor comprising a sensor element according to the present invention and an annular metal holder fitted to the sensor element, wherein a metal layer surrounding an outer peripheral portion of the sensor element is provided. The sensor element is provided, and the metal layer and the metal holder are fixed by brazing.

The operation mode of the sensor element is not particularly limited.
For example, an oxygen ion permeable sensor element or an oxide semiconductor sensor element may be used.
Also, the shape of the sensor element is not particularly limited, and may be, for example, a flat plate, a prism, a column, a cylinder, or the like. A flat sensor element is preferable because it is easy to manufacture. In the manufacture of the sensor element, materials commonly used in the manufacture of oxygen concentration sensors, such as zirconia, alumina,
Titania or the like can be used alone or in combination. The electrodes may be formed by a printing method using a platinum paste or the like.

The metal layer can be formed, for example, by screen-printing a tungsten paste or a silver paste, and usually has a linear or band shape. The number of linear or band-shaped metal layers may be one, but two or more may be provided. The position where the metal layer is provided is appropriately selected.

The method of providing a metal layer on the sensor element is appropriately selected according to the properties of the sensor element so that a sensor element having predetermined performance can be obtained. For example, a metal layer may be directly provided on the sensor element, or, for example, after a metal layer is provided on the surface of an appropriate ceramic green sheet, the sensor element may be provided with the ceramic green sheet having the metal layer on the surface side. It may be attached to the sensor element so as to surround it, and then fixed by firing.

The metal holder can be made of a corrosion-resistant metal material, such as stainless steel, nickel, or the like, using a conventional processing method, for example, machining, and has a ring-shaped center portion having a through hole that can be fitted with the sensor element. Things. The size and shape of the metal holder are appropriately selected in consideration of the size and shape of the sensor element and the casing.

[0013] The brazing material for brazing and fixing the metal holder to the metal layer portion is selected according to the material of the metal holder and the metal layer so as to obtain strong adhesion between them. Usually, for example, a nickel brazing material or a copper brazing material can be used.

The brazing between the metal holder and the metal layer can be performed by a conventional method, for example, by heating in an electric furnace.

[0015]

In spite of the difference in shape between the sensor element and the metal holder, for example, even when the sensor element is flat,
At the metal layer portion, an annular metal holder is firmly brazed and fixed to the sensor element.

[0016]

The present invention will be described in more detail with reference to the following examples.

FIG. 1 shows an example of a sensor element of the laminated zirconia oxygen concentration sensor of the present invention. FIG. 1A is a top view of the sensor element 1, and FIG. 1B is a partially broken front view of the sensor element 1. The sensor element 1 includes a ceramic substrate 11 having a heater 7 therein for heating the sensor element 1 at an appropriate temperature, and platinum electrodes 5 and 6 on both surfaces by screen printing.
The zirconia sheet 9 on which the zirconia sheet 9 is formed is laminated by providing an air introduction portion 8, and a protective layer 12 is provided on the surface of the zirconia sheet 9 on the platinum electrode 5 side. An alumina sheet 2 provided with a metal layer (not shown) was wound around the outer periphery of the zirconia sheet 9, and a metal holder 3 was fixed to the alumina sheet 2 by brazing at a brazing portion 4 (metal layer portion). Reference numeral 10 denotes an electrode take-out portion, and platinum electrodes 5, 6
And the zirconia sheet 9 and the protective layer 12 were electrically connected by pinholes. The sensor element 1 measures the oxygen concentration in the exhaust gas based on the oxygen concentration difference between the platinum electrode 5 side to which a gas to be measured, for example, an automobile exhaust gas is applied, and the platinum electrode 6 on the atmosphere side (reference). .

FIG. 2 shows an embodiment of the laminated zirconia oxygen concentration sensor of the present invention using the sensor element 1. In this oxygen concentration sensor, the tapered portion of the metal holder 3 is brought into close contact with the tapered portion of the inner wall of the sensor holder 13, and a filler 14 such as talc is applied to the sensor element 1 and the sensor holder 13.
The sensor element 1 is assembled by fixing it with a spring 15 and further providing a caulking portion 16. In addition, 17 is a lead wire take-out part, 18 is a lead wire, 19 is a bush, and 20 is an outer cylinder. In use, the sensor holder 13 is screwed to, for example, an exhaust pipe 21 of an automobile, and the protective cover 22
The oxygen concentration of the exhaust gas impinging on the sensor element 1 through the hole 23 is measured.

FIG. 3 shows an example of a method for manufacturing a sensor element of the laminated zirconia oxygen concentration sensor of the present invention. FIG.
As shown in FIG. 3B, an alumina green sheet 25 is wound around a green sheet molded body 24 provided with the electrode take-out part 10 shown in FIG. At this time, a metal layer 26 is provided in advance on a predetermined portion of the alumina green sheet 25 opposite to the side in contact with the green sheet molded body 24 by a screen printing method using a metal paste (for example, a tungsten paste or a silver paste). deep. When the green sheet molded body 24 around which the alumina green sheet 25 is wound is fired in a furnace under predetermined firing conditions, the sensor element 1 shown in FIG. 3C is obtained. Next, as shown in FIG. 3D, the metal holder 3 is fitted to the alumina sheet 2 and placed on the metal layer 26, and the brazing material 27 (for example, a nickel-based brazing material or a copper-based brazing material) is And the gap between the metal holder 3 is filled. Next, as shown in FIG.
The sensor element 1 is put into the
Is closed, and the pressure is reduced to a predetermined condition by the vacuum pump 31. Next, the brazing material 27 is melted by heating by the heater 32, and the metal holder 3 is brazed and fixed to the metal layer 26 by the brazing portion 4.

In this embodiment, the alumina green sheet 2
5 was wound around a green sheet molded body 24 (zirconia is reduced when heated in vacuum to deposit zirconium), but when the sensor element is formed of an alumina substrate, the alumina green is used as in this embodiment. Sheet 25
Need not be wound around the green sheet molded body 24,
The metal layer 26 may be provided directly on the sensor element so as to surround the outer peripheral portion in a direction orthogonal to the length direction of the sensor element.

[0021]

According to the stacked oxygen concentration sensor of the present invention, a metal layer surrounding the outer periphery of the sensor element is provided on the sensor element.
Since the metal layer and the metal holder are brazed and fixed, the metal holder can be firmly brazed and fixed to the sensor element regardless of the shape of the sensor element and the metal holder. For this reason, even when the sensor element is easy to manufacture and has a flat shape with high productivity and the metal holder is annular, without any processing of the sensor element,
An annular holder formed using a metal having excellent workability can be easily fixed with high sealing performance without limiting the conditions such as firing or degreasing of the sensor element.

Further, in the stacked oxygen concentration sensor of the present invention, since a metal holder having excellent heat conductivity and workability can be used, the degree of freedom in designing the holder part is increased. By adjusting the degree of heat sink from the sensor, the heat fluctuation of the sensor element is suppressed,
Sensor characteristics can be maintained in a good state.

Further, since the metal holder can be pressed directly onto the sensor holder when the sensor element is mounted, the metal holder can be used for sealing and cushioning the seal ring and the like which have been conventionally used for mounting the sensor element. This member is unnecessary, and the assembly of the sensor element is simplified.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an example of a sensor element of a laminated zirconia oxygen concentration sensor of the present invention.

FIG. 2 is a cross-sectional view of one embodiment of the laminated zirconia oxygen concentration sensor of the present invention.

FIG. 3 is an explanatory view of a manufacturing process of an example of the sensor element of the laminated zirconia oxygen concentration sensor of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Sensor element 2 Alumina sheet 3 Metal holder 4 Brazing part 5, 6 Platinum electrode 7, 32 Heater 8 Atmospheric introduction part 9 Zirconia sheet 10 Electrode extraction part 11 Ceramic substrate 12 Protective layer 13 Sensor holder 14 Filler 15 Spring 16 Caulking Part 17 Lead wire take-out part 18 Lead wire 19 Bush 20 Outer cylinder 21 Exhaust pipe 22 Protective cover 23 Hole 24 Green sheet molding 25 Alumina green sheet 26 Metal layer 27 Brazing material 28 Furnace 29 Space part 30 Packing 31 Vacuum pump

Claims (1)

(57) [Claims] In a stacked oxygen concentration sensor comprising a sensor element and an annular metal holder fitted to the sensor element, a metal layer surrounding an outer peripheral portion of the sensor element is provided on the sensor element. A stacked oxygen concentration sensor, wherein a metal layer and the metal holder are fixed by brazing.