JPH02112636A - Air-fuel ratio sensor - Google Patents

Abstract

PURPOSE:To contrive the improvement of reliability preventing corrosion in a signal pickup part with a relay lead easily connected by metallizing by forming a recessed part in an opening end face of a detecting element in an air-fuel ratio sensor while specifying the recessed part in its shape and size. CONSTITUTION:A detecting element 13 in an air-fuel ratio sensor of limit current type provides platinum porous electrodes 21, 22 respectively in inner and outer surfaces of a bag pipe-shaped zirconia solid electrolyte 20 while diffused resistors in an upper part of the outer side electrode 22. Here the detecting element 13 forms in its opening end face two recessed parts. When each recessed part is set in its bottom face diameter (b) to 1.5mm or more, a value is set respectively with ratio of an upper face diameter (a) to the bottom face diameter (b) to 1.5 or more, depth (h) to 2mm or less and a tilt angle theta to 60 deg. or less. While a signal pickup metal part 8b is baked by precious metal paste 23 and connected by metallizing to each electrode 21, 22 in each recessed part. Further the connection part is protected to be sealed with glass coating 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio sensor, and particularly to a limiting current type air-fuel ratio sensor suitable for controlling the air-fuel ratio of internal combustion engines such as automobiles.

[Conventional technology]

In the air-fuel ratio sensor, the signal extraction structure is similar to that previously devised by the applicant of the present invention in U.S. Pat.
Dimensions were not specified.

[゛Problem to be solved by the invention]

The above-mentioned prior art provides two recesses on the end face of the detection element, extends the inner and outer electrodes to the recesses, and directly metallizes and joins the signal extraction metal member to the electrodes within the recesses using noble metal paste. Reliability can be improved by sealing and protecting the joint with a glass coating, but since the shape and dimensions of the recess are not specified, organic matter in the precious metal paste and glass coating material may escape during firing. However, there were manufacturing problems such as the fact that the shape and dimensions of the recess greatly affected the shape and dimensions of the recess.

An object of the present invention is to provide an air-fuel ratio sensor capable of detecting air-fuel ratios over a rich to lean range and improving reliability.

[Means to solve the problem]

The above object is to provide a limiting current type air-fuel ratio sensor having a detection element in which platinum porous electrodes are provided on the inner and outer surfaces of a bag-tubular zirconia solid electrolyte and a diffusion resistor is further provided on the outer electrode. When the lower surface diameter of this recess is 1.5 volumes or more, the ratio of the upper surface diameter to the lower surface diameter is 1.5 or more, the depth is 2ffI11 or less, and the inclination angle is 60 degrees or less, and the inner surface of the recess is The above-mentioned inner and outer electrodes are respectively formed, and a metal member for signal extraction is baked onto the electrodes in each recessed portion to metallize and bond them, and the bonded portions are further sealed and protected with a glass coating. did.

[Effect]

The shape and dimensions of the concave portion on the end face of the detection element are based on noble metal paste,
When firing the glass coating material, we have specified a shape with 9 dimensions that will allow the organic matter contained therein to escape easily.This makes metallization bonding and glass sealing possible, resulting in a highly reliable signal extraction structure, and a wide range from rich to lean areas. Fuel ratio can be measured with high reliability.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to FIGS. 1 to 4.

FIG. 1 is a vertical cross-sectional view of the overall configuration of an embodiment of the air-fuel ratio sensor of the present invention. In FIG. 1, a detection element 13 is housed in a plug 14 with a washer 15 interposed therebetween. The detection element 13 has a bag tube shape, and the opposing inner and outer surfaces are provided with
Porous platinum is formed as an electrode by plating,
The inner and outer electrodes are formed to extend to the element opening end face. Further, on the outer electrode, a diffusion resistor that controls the rate of gas diffusion is formed by plasma spraying or the like. Detection element 1
A ceramic heater 16 is inserted to control the temperature at a constant temperature, and a heater lead 10 for power supply is brazed to the ceramic heater 16, and a ceramic heater flange 11 for positioning is bonded to glass. are joined together. The metal parts for extracting the signal from the detection element 13 (Nickel) or the platinum relay leads 8a, 8b, which are precious metal parts, are connected to inner and outer electrodes by baking platinum paste in two recesses provided on the end face of the element. They are metallized and bonded, and the recesses are coated with glass and sealed.

The metallized joints formed by this glass sealing are designed to have improved corrosion resistance, heat resistance, and tensile strength. The relay leads 8a, 8b and the heater lead 10 are
Each lead wire 1 is crimped by a crimping sleeve 4. After crimping, a small amount of silver solder is applied to the crimped part to improve the reliability of the electrical connection. Relay lead 8a,
8b and the heater lead 10 are insulated from each other and housed in the ceramic insulator 5. A gasket 12 is inserted between the heater flange 11 and the insulator 5, a disc spring 3 made of a heat-resistant material is placed on the scrap part of the insulator 5, and an outer cylinder 7 having an air introduction hole 6 is placed above it. The outer cylinder 7 is crimped to the stopper 14, and the insulator 5° and the ceramic heater 16 are fixed under pressure. There are a total of four lead wires 1, which pass through a grommet 2, are drawn out to the outside of the sensor, and are connected to a sensor drive module (not shown). In addition, the sensor has a detection element 1
A protective cover 17 for protecting the tip of the stopper 3 is crimped and fixed to the stopper 14.

2 is a vertical cross-sectional view showing an example of the detailed structure of the signal extraction section A in FIG. 1, FIG. It is a flowchart of the manufacturing method.

Next, a lead bonding method for the signal extraction section will be explained using FIGS. 2 to 4. First, a zirconia electrolyte 20 having two recesses on the open end surface of a bag tube type element is prepared. Here, the dimensions and shape of the two recesses on the opening end face of the detection element are as shown in Fig. 3, with a lower surface diameter of 1.5 tin or more, a ratio of the upper surface diameter a to a lower surface diameter 21+11
Hereinafter, the inclination angle θ is defined as 60 degrees or less. If the diameter of the bottom surface is 1.5 m or less, the area to be metallized and bonded becomes small and the tensile strength becomes weak. Additionally, the organic matter contained in the platinum paste becomes difficult to burn.

The metallization bonding condition deteriorates. If the ratio of the upper surface diameter a to the lower surface diameter S is less than 1.5, the combustion of organic matter contained in the platinum paste will be poor, metallization bonding will be difficult to achieve, and the tensile strength will be weakened.

When the depth h is 2 cm or more, the tensile strength becomes weak as described above. The same applies when the angle of inclination θ is 60 degrees or more. Porous electrodes 21 and 22 are formed on the inner and outer surfaces of the zirconia electrolyte 2° by chemical plating with platinum. At this time, the inner electrode 21. An outer electrode 22 is formed. Next, a jig for fixing the element is set. In the case of a Ni relay lead, a carbon jig, which is a heat-resistant material, is used, and in the case of a platinum relay lead, an alumina jig, which is a heat-resistant material, is used.

In this state, the recesses are filled with platinum paste 23. The platinum paste 23 contains about 2 to 10% of a glass component, and the filling amount is about 172 times the depth of the recess. Next, a relay lead 8b made of soft Ni wire or platinum wire with a wire diameter of 0.6 mm whose head is shaped like a nail's head by header processing is coated with platinum paste 2 in the state shown in FIG.
3 and placed in contact with the element outer electrode 22. Next, in order to prevent the relay lead 8b from falling down, a jig for fixing the lead is set, and the relay lead 8b is placed in an electric furnace for metallization. In the case of Ni wire, the firing atmosphere is an air atmosphere to help burn the organic components contained in the platinum paste 23 up to 300°C, and when the temperature exceeds 300°C, N2 gas is flowed to prevent oxidation of the Ni wire, and NzlOO% The atmosphere was changed to 1100° C., and firing metallization was performed at 1100°C. Thereafter, when the temperature reaches 300°C, the atmosphere may be returned to air.

In addition, in the case of platinum wire, firing metallization is performed at 1100°C in an air atmosphere. Once the steps up to this point are completed,
The relay lead 8b is connected to the outer electrode 2 via the platinum paste 23.
2 and metallization bonded. The metallization bonding between the relay lead 8a and the inner electrode 21 is also performed simultaneously in exactly the same manner.

The strength of these metallized joints is 1 kgf/m
”The tensile strength is set to 4 kgf/m because it is weak below
Glass sealing is performed as the next step for the purpose of increasing the temperature to 8rt and preventing corrosion of the metallized part.A sealing glass 9 is applied to the metallized part of the element after metallized bonding is completed.
Filled with 100% molten metal, set it in the jig used for metallization bonding, and placed it in the electric furnace for firing. It is fired and sealed at 650°C in an electric furnace. The atmosphere in the furnace is the same as that during metallization bonding. With the above, the outer electrode 2'2. The connection of the signal extraction relay leads 8b and 8a to the inner electrode 21 is completed.

In other embodiments, the platinum paste 23 can be replaced with a noble metal paste such as silver/palladium paste, silver thread paste, gold thread paste, etc.

In this case, the temperature for metallization bonding must be appropriate for each paste. Further, in the case of a Ni wire relay lead, if a platinum foil or the like is bonded in advance to the portion in contact with the element electrode surface before metallization, the reliability of the signal extraction portion can be further improved.

〔Effect of the invention〕

According to the present invention described above, since the size and shape of the concave part of the signal extraction part of the air-fuel ratio sensor detection element is specified, the relay lead can be easily metallized and bonded, so that the signal due to salt water, moisture, etc. that has entered through the air inlet hole is Corrosion of the take-out part is prevented, and air-fuel ratios in the rich to lean range can be measured with high reliability.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of the overall configuration of an embodiment of the air-fuel ratio sensor of the present invention, FIG. 2 is a vertical cross-sectional view of an embodiment of the detailed structure of the signal extraction section A of FIG. 1, and FIG. 2 is a dimensional and shape diagram of the recessed portion of the signal extraction portion in FIG. 2. FIG. FIG. 4 is a flowchart of the manufacturing method. 6...Atmospheric introduction hole, 8a, 8b...Relay lead, 9
Sealing glass, 13... Detection element, 14... Plug, 16... Ceramic heater, 20... Zirconia electrolyte, 21... Inner electrode, 22... Outer electrode,
23...Platinum paste.

Claims (1)

[Claims] 1. In a limiting current type air-fuel ratio sensor having a detection element in which platinum porous electrodes are provided on the inner and outer surfaces of a bag-tubular zirconia solid electrolyte and a diffusion resistor is further provided on the outer electrode, two When a recess is provided and the lower surface diameter of the recess is 1.5 mm or more, the ratio of the upper surface diameter to the lower surface diameter is 1.5 or more, the depth is 2 mm or less, and the inclination angle is 60 degrees or less. An empty space characterized in that outer electrodes are formed respectively, a metal part for signal extraction is baked onto the electrodes in each of the recesses to metallize and bond them, and the bonded parts are further sealed and protected with a glass coating. Fuel ratio sensor.