JPS6015552A - Output adjustment of oxygen concentration detecting element - Google Patents

Abstract

PURPOSE:To obtain a limit current type element having accurate output in good yield, by a method wherein an oxygen concn. detecting element is assembled in a configuration capable of obtaining output and, thereafter, the terminal part of said element containing gas diffusion orifices or a gas diffusion layer is cut off in a dimension capable of obtaining required output. CONSTITUTION:For example, a cathode 2 and an anode 3 are formed at positions respectively opposed to the front and back surfaces of a solid electrolyte cell 1. A heater 6, an opening 5' corresponding to the cathode 2, a ceramic plate 5 having a slit coming to a long diffusion slot 8 continued to said opening 5' are provided on the cell 1 and a heat resistant ceramic plate 4 is subsequently superposed and connected to said cell 1. A ceramic plate having an opening 7' at a position corresponding to the anode 3 is connected to the under surface of the cell 1 to perform the assembling of an element. In the next step, the limit current value of the element is at first measured in the atmosphere and the element is cut off in an arbitrary length of l1mm. as shown by the broken line B to measure a limit current value while a cut-off length lx for obtaining an effective diffusion orifice 8 required in showing required output is subsequently calculated to cut the element along an one-dotted chain line C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention d relates to a method for adjusting the output of a limiting current type oxygen concentration detection element for detecting @ element concentration in a gas atmosphere.

[Prior art]

Oxygen concentration detectors are used to control the air-fuel ratio and purify exhaust gas in internal combustion engines such as automobiles, and to control the combustion state of boilers. Various oxygen concentration detectors are known, one of which has been developed as a limiting current type oxygen concentration detector. This limiting current type oxygen concentration detector has electrodes on both sides of an oxygen ion-permeable solid electrolyte to form the element body, and when a constant voltage is applied between both electrodes of the element body, one electrode (cathode) side Since oxygen ions permeate through the other electrode (anode) gill, at least one of the electrodes enters (or exits).
This method takes advantage of the fact that when the element ion i is limited, a limiting current flows between the two electrodes depending on the concentration of boron in the gas to be measured. In this limiting current type e-element detector, a method for controlling the diffusion rate of oxygen to one electrode surface of the element body is, for example, using electrodes formed on both sides of a disk-shaped solid electrolyte cell. This method involves directly forming a porous ceramic coating layer on the surface by plasma spraying, or by arranging a diffuser plate with pores formed in a ceramic film on the electrode surface.

However, the diffusion layer made of the ceramic coating layer and the diffusion plate with diffusion holes are not ultimately incorporated into the shape of the detection element due to variations that occur in each process of forming them and each subsequent process. At that stage, there were large variations in the output. Therefore,
Conventionally, methods of manufacturing devices with no difference in output have been considered.

[Purpose of the invention]

The present invention is intended to meet the above-mentioned conventional demands, and provides a method for adjusting the output of a limiting current type oxygen concentration detection element, which allows the desired output to be easily obtained after assembling the zero element in a form that provides the output. This is what we intend to provide.

[Structure of the invention]

The method for adjusting the output of the limiting current type oxygen concentration detection element of the present invention is to assemble the element in a form that provides an output, and then adjust the end of the element containing the diffusion hole or diffusion layer formed to a sufficient length to the required length. It is characterized by cutting off so that output can be obtained.

As mentioned above, the limiting current type oxygen concentration detector is constructed by providing the element body with air-permeable thin film electrodes made of platinum or the like in correspondence with each other on the front and back sides of a solid electrolyte cell such as zirconia. When a voltage is applied between the electrodes, oxygen ions permeate from the negative electrode side to the positive electrode side, and a current flows between the two electrodes. However, if the amount of oxygen ions that permeate is limited,
This method captures the phenomenon in which the current increases in proportion to the increase in voltage up to a value of It is something to do.

This limiting current value (output) is calculated by the following formula: iz father L” CI) (However, L indicates the depth of the diffusion hole or the thickness of the diffusion layer.) It is known that there is a relationship expressed by

The output t is proportional to the amount of oxygen that reaches the cathode surface through the diffusion holes or the diffusion layer. In other words, the greater the amount of oxygen, the greater the output. Note that the diffusion layer is also considered to be a collection of thin diffusion holes. Therefore, when considering the diffusion hole as a thin tube as shown in Fig. 6, the amount of gas passing through the diffusion hole Q is proportional to its area S, but also proportional to its length L', so QCC8/L ' Since it is QCC4z, the relationship is as shown in the above equation (2).

In the above, when the area S is constant, the length L' of the diffusion hole (
Alternatively, if L) is shortened, the amount of gas passing through the diffusion hole increases accordingly, so the output can be changed. The present invention was completed based on this knowledge.

〔Example〕

The present invention will be explained below with reference to Examples.

As a first embodiment, what is shown in FIGS. 1 and 2 is as follows.
This is an example of a detection element formed into a flat plate according to a typical embodiment of the present invention.

Figure 2 is an exploded perspective view showing the configuration of the detection element.
1 is a solid electrolyte cell formed into a plate shape, and a negative electrode 2 and a positive electrode 3 are formed on both the front and back surfaces of the cell in corresponding positions and areas to constitute the device body. The numeral 5 located at the top of the cell 1 is a heat-resistant ceramic plate with a heater 6, and is provided with a slit that becomes a long diffusion hole 8 that extends from a window 5' opening corresponding to the electrode of the cell 1 to the end. There is. This ceramic plate with heater 6 constitutes a ceramic heater by laminating and laminating it with a heat-resistant ceramic plate 4 shown above. 7 below the cell 1 is a heat-resistant ceramic plate that similarly has a window 7' at a portion corresponding to the electrode.

A ceramic heater consisting of these ceramic plates 4 and ceramic plates 5 with heaters 6, a cell 1, and a ceramic plate 7
are bonded together using glass having a softening point of about 800° C., for example, as an adhesive to form a plate-shaped detection element as shown in FIG.

In addition, in the above process, zirconium oxide powder made by Cell 1 Co., Ltd. and indium oxide containing 800 g of ruthi is compacted according to a conventional method and sintered at about 1600°C. Also,
The ceramic plates 4, 5.7 can be made in the same manner as the cell 1 using ceramic powder having the same coefficient of thermal expansion as the cell 1. The heater 6 is formed by printing a paste obtained by kneading powder such as platinum-rhodium with an organic solvent using silk screen printing or the like.

The output of the detection element S assembled as described above is adjusted by cutting off a predetermined amount at the end where the diffusion hole 8 opens, as shown in FIGS. 1 and 2.

The amount of cut off is determined as follows.

First, for the completed element, the limiting current value (output) (CAm) in the atmosphere, for example, is measured.

Next, the end of this element is cut off by an arbitrary length t5 mm from the opening end of the diffusion hole as shown by the broken line B, and then the output (Bm) is measured.

As mentioned above, the limiting current value it is determined by the depth L and I of the diffusion hole.
Since the relationship is L(X L-', the effective diffusion hole Lx (mm) of the element after cutting is calculated by the following formula: (Lz+4
) B 0. -1-(If)Lx A is requested.

Assuming that the required output (limiting current value) is am people, the length 1X to be cut further can be calculated by using the following formula from the formulas of Tonashi and Tonashi, formulas ■ and formulas, similar to the above formula ■. ■: It is expressed by and can be determined by solving this equation (■). In the figure, a dashed-dotted line C indicates the cutting position to obtain the intended detection element.

Similarly, the method of the present invention can adjust the output of a limiting current type oxygen concentration detecting element as shown in FIGS. 3 to 5.

FIG. 3 is a cross-sectional view showing a second embodiment of the present invention, in which a solid electrolyte cell 1 formed into a cylindrical shape with one end closed is provided with a negative electrode 2 on the outside and a positive electrode 3 on the inside. An example is shown in which a detection element is mounted in a cylindrical ceramic housing 10 containing a porous ceramic filter 9 as a diffusion layer, and line B is similar to the first embodiment.

Cut off the end of the element on the filter 9 side according to step C to adjust the output.

FIG. 4 shows a third embodiment, in which the cell 1 has the same shape as the second embodiment.
A ceramic capillary tube 12 with a negative electrode 2 on the inside and a positive electrode 3 on the outside has a narrow diffusion hole 8 to control the rate of gas diffusion.
This is an example where .

This ceramic capillary tube 12 is cut to adjust the output. In addition, 11 shows a support body.

FIG. 5 shows an example in which a ceramic molded body 13 provided with diffusion holes 8 is used in place of the ceramic filter used in the second embodiment 1 of FIG. 3 in the fourth embodiment. Similarly, the output is adjusted by cutting off the opening side end of the diffusion hole 8. In addition,
In FIGS. 3 and 5, 6 indicates a heater (heating element) such as a nichrome wire.

(Effects) As described above, according to the present invention, the output can be adjusted after manufacturing a complete element, and the adjustment method is simple, and a detection element having the desired output can be easily obtained. Therefore, it also eliminates the need to strictly control the ceramic material, particle size, etc. for 7-lasma spraying, or to unnecessarily strictly control the element assembly process, as in the past. .Also,
In the conventional method, if the obtained device did not have a predetermined output, it could not be used as a defective product, but according to the method of the present invention, such waste can be eliminated.

[Brief explanation of the drawing]

FIG. 1 is an exploded layer perspective view of a detection element showing a first embodiment of the present invention. FIG. 2 is a perspective view of a detection element of the first embodiment.
5 and 5 are cross-sectional views of a detection element showing other embodiments of the present invention, and FIG. 6 is a schematic diagram of gas diffusion holes. In the figure, 1... Solid electrolyte cell 2.3... Electrode 4.5, 7... Ceramic plate 6...
... Heater 8 ... Diffusion hole 9 ... Ceramic filter Patent applicant Toyota Motor Corporation representative Patent attorney Yumi Sakai (and one other person) Fang 1 Fang 2 Fig. Fang 3 Fig. Fang 4 Fig. Fang 5 Fig. 6

Claims (1)

[Claims] A method for adjusting the output of a limiting current type concentration detection element, which comprises assembling the element in a form that provides an output, and then cutting off an end of the element including a diffusion hole or a diffusion layer in order to obtain a required output.