JPH0522178B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxygen sensor for measuring oxygen concentration in a gas to be measured such as exhaust gas. More specifically, the present invention relates to an oxygen sensor that can measure air-fuel ratio and the like over a wide range and with great precision.

In order to improve the fuel efficiency and purify exhaust gas of automobile engines, a method has been proposed in which the air-fuel ratio of the intake air-fuel mixture is operated on the lean side, which is higher than the stoichiometric air-fuel ratio (excess air ratio λ = 1). There is a need for an oxygen sensor that can accurately measure air-fuel ratio.

One of the oxygen sensors for such use is the one published by Ford Corporation of the United States (for example, Japanese Patent Application Laid-Open No. 130649/1983).

This sensor consists of two plate-shaped oxygen ion conductive solid electrolyte sintered bodies with electrodes on both sides, one as an oxygen pump element and the other as an oxygen concentration battery element.
The two plate elements are laminated and bonded with a plate spacer made of a heat-resistant material with a small hole bored in the side wall sandwiched therebetween, thereby forming an enclosed chamber and an oxygen diffusion hole between the two plate elements. Then, by energizing the oxygen pump element and allowing the flow of oxygen by diffusion between the outside atmosphere, that is, the atmosphere to be measured through the hole, the oxygen in the enclosed chamber is transferred to the output of the oxygen concentration battery element, ie, the output of the oxygen concentration battery The oxygen concentration in the gas to be measured is electrically measured by pumping the oxygen so that the ratio of the oxygen concentration between the gas and It is. This type of sensor is
Since the oxygen pump element and the oxygen concentration battery element are provided separately, this is advantageous in terms of the temperature dependence of the sensor output on the ambient gas temperature.
However, because the material of the spacer is different from that of both elements, and because a glass adhesive or ceramic adhesive is used to bond both elements to the spacer, the adhesive surface is vulnerable to thermal shock and easily peels off, making it difficult to bond the elements to the spacer. There are some drawbacks such as difficulty in maintaining the airtightness of the chamber, and it cannot be said to be completely satisfactory in terms of manufacturing and structure.

The present invention provides an oxygen sensor that is easy to manufacture, has excellent responsiveness and durability, has large oxygen diffusion holes to eliminate clogging, and consumes less power.

Two oxygen ion conductive solid electrolyte plates for an oxygen pump element and an oxygen concentration battery element, each having heat-resistant metal layers for electrodes and their lead wires on both sides using thick film technology, are An intermediate plate-like body, which does not include a heating resistor and is made of ceramic material, is sandwiched between a relatively large hole and one or more relatively small holes, which are also in the thickness direction and communicate with the hole on the side of the hole. Laminated and integrally sintered, the tip side and the base side are distinguished, and the tip side has a flat enclosed chamber with a vertical width equal to the thickness of the chamber and communicates the chamber with the outside world. In addition to forming communication holes in the chamber, oxygen permeable walls of an oxygen pump element or an oxygen concentration battery element are formed on both walls in the thickness direction of the chamber, to which a voltage is applied or taken out from the source side via a lead wire. It is characterized by:

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on drawings showing one embodiment.

FIG. 1 is an exploded perspective view for explaining an embodiment of the oxygen sensor of the present invention.

In the figure, 2 is a plate-shaped body for the oxygen pump element 1, which has a porosity of 0 to 10% and is made of, for example, Y ₂ O ₃ , CaO, MgO.
ZrO ₂ stabilized or partially stabilized with
It is a plate-shaped oxygen ion conductive solid electrolyte made of ThO ₂ with a final thickness in the range of approximately 0.1 to 2.0 mm, here 0.5 mm, and both sides are coated with heat-resistant metals such as Pt, Ru, Pd, Rh, Ir, etc. Au, Ag, etc. (here
A layer 3 of Pt) is provided using thick film technology as an electrode 3a, a lead wire 3b, and lead wire extraction portions 3c and 3d. The heat-resistant metal layer 3d for the take-out portion is electrically connected to the heat-resistant metal layer on the back surface of the plate-like body 2 by platinum paste filled in through holes (not shown) of the plate-like body 2. Reference numeral 5 designates a plate-shaped body for the oxygen concentration measuring battery element 4, which is an oxygen ion conductive solid electrolyte having the same composition and shape as the oxygen pump element 1, and has electrodes 6a, lead wires 6b and A heat-resistant metal layer 6c for the lead-out portion of the lead wire is also provided using the thick film technique. The heat-resistant metal layer has a thickness of 5 to 20 μm and a porosity of 10.
40% is preferable because it ensures electrical conductivity in the direction parallel to the electrode layer and at the same time includes sufficient oxygen gas ventilation holes to the solid electrolyte surface.
The porosity was measured using a (mercury intrusion type) porosimeter. 7 is an intermediate plate-shaped body made of the same material as the oxygen concentration battery element 4 and oxygen pump element 1, and has a final thickness of approximately 0.1 to 2.0 mm;
Here, it is made of 0.5mm. This is not provided with a heat generating resistor or an electrode for taking out the heat generating resistor, but is placed in the thickness direction at a portion corresponding to the installation position of the electrodes 3a and 6a provided in the oxygen concentration battery element 4 and oxygen pump element 1. A relatively large punched hole 8 is provided, and a plurality of relatively small holes 9, here three, also punched in the thickness direction, communicating with this hole laterally, are provided. The shape of the relatively small hole 9 when viewed in the direction along the plane is advantageous in that the vertical width is the same as the thickness, which improves responsiveness and prevents performance deterioration due to clogging caused by combustion residue in the exhaust gas. However, it is further desirable that the final value of the total cross-sectional area of the communicating holes be larger than 1 mm ² , more preferably 3 mm ² or more. When it is smaller than 1 mm ² , responsiveness is significantly reduced and clogging is likely to occur. Here, the final dimensions are 0.5mm x 2mm x 3 (hole length is 1mm)
And so. FIG. 2 is a perspective view of the oxygen sensor of this embodiment after these components are laminated and integrated. In this figure, reference numeral 9 indicates a relatively small hole in the intermediate plate that ultimately forms the communication hole of the sensor of the present invention. Reference numeral 10 indicates a lead wire brazed to the lead-out portion of the lead wire, 11 indicates the front side of the sensor, and 12 indicates the base side of the sensor.

The oxygen sensor of the present invention is manufactured, for example, as follows. That is, for example, a solid electrolyte powder mixed with 4 to 15 mol% of a stabilizer such as Y ₂ O ₃ , CaO, MgO powder, etc. is kneaded with a binder for a doctor blade, and then extruded to a predetermined thickness by a known extrusion method. An unfired plate-like body is formed. Next, each unfired plate-shaped body is punched out and a card-shaped product 1 of approximately 80 mm x approximately 60 mm
3 and 13', and three fixing holes 14 for positioning are also simultaneously punched in the upper and lower parts thereof. Furthermore, a through hole is punched in the lead-out portion for the inner electrode lead wire. After that, as shown in FIG. 4, one card-shaped product 13 is coated with four heat-resistant metal layers 3, for example.
5 to 30% by weight of co-base powder to platinum powder,
Here, electrodes 3a, 3b, 3c, 3d are provided by printing a heat-resistant metal layer paste containing 20% by weight, and a relatively large hole 8 is formed in another card-shaped product 13' as shown in FIG. , 3 extending from the side of the hole 8
Four relatively small holes 9 are simultaneously punched out. Card-shaped product 1 with holes 8 and 9 punched out
3' is sandwiched between card-shaped products 13 on which a heat-resistant metal layer 3 is printed on both sides, and the binder solvent used during molding is applied, and the products are pasted together as shown in FIG. 6, and then cut along the cut line 15. 1,400~
It is fired at 1,600°C for about 4 hours and is finished in the form shown in the perspective view in Figure 2. In addition, only the outer electrode surface or, in some cases, both the inner and outer electrode surfaces may be coated with the same material as the plate material or alumina,
A porous ceramic protective film made of spinel or the like is printed as necessary. When this ceramic protective layer is provided on the outer surface of the electrode, it can also be provided by thermal spraying after firing.

FIG. 3 is a layout diagram for explaining the usage state of the oxygen sensor of the present invention installed in an exhaust gas pipe (not shown). In this usage state, the sensor of the above example, that is, the thickness of the enclosed chamber is 0.5 mm, and the cross-sectional area of the chamber viewed from the thickness direction (approximately equivalent to the electrode area of the oxygen pump element and oxygen concentration battery element) is 100mm ² , cross section of oxygen diffusion hole 0.5mm x 2
mm x 3 (hole length 1mm), thickness 15μm, evaporation rate 30
Using a sensor with a zirconia oxygen pump element partially stabilized with Y ₂ O ₃ and an oxygen concentration cell element with a porous electrode of % platinum and a thickness of 0.5 mm,
A DC voltage of 10 volts is applied between the electrodes of the oxygen pump element 1 via a variable resistor R, and the current I flowing through the element 1 is varied from 0.05 mA to 10 mA to remove oxygen from the atmospheric gas in the enclosed room. The oxygen concentration in the external gas to be measured is approximately 0.05 to 10% under the condition that the output voltage of the other oxygen concentration battery element 4 is constant at 20 millivolts when pumped out.
It was hot. The correspondence between the two was linear on a logarithmic scale. The temperature of the sensor was maintained at 800°C.

In the above example, the material of the intermediate plate-like body was the oxygen ion conductive solid electrolyte material for oxygen pump elements and oxygen concentration battery elements, but the sintering temperatures were not far apart and the coefficient of thermal expansion was approximately the same. Similar dissimilar ceramic materials such as alumina and spinel can also be used.

The oxygen sensor of the present invention has the following characteristics: the oxygen partial pressure of the atmosphere to be measured to which the sensor is exposed; (a quantity directly related to the amount of oxygen molecules transferred through the pump element), and the atmosphere to be measured is defined as the partial pressure of oxygen in the enclosed chamber communicating with the hole and the partial pressure of oxygen in the atmosphere to be measured. This method attempts to measure the oxygen partial pressure in the atmosphere being measured by utilizing the fact that the ratio of Therefore, not only the method described in the above embodiment but also other methods are applicable, for example, under conditions where the pumping current of the oxygen pump element is controlled to be constant, the oxygen partial pressure in the atmosphere to be measured corresponds to the output of the oxygen concentration battery element. It is also possible to provide a method that utilizes this fact.

As described above, the oxygen sensor of the present invention is formed by a laminated and integrated sintering method of ceramic sheets, and has a communicating hole whose enclosed chamber has a flat shape and whose vertical width is equal to the thickness of the chamber. It is possible to measure oxygen concentration with a relatively small pumping current of the oxygen pump element, with a cross-sectional area that does not have to worry about performance deterioration due to clogging, and while keeping response within a practical range (e.g., response time of approximately 0.5 seconds or less). Since the intermediate plate does not have a heating resistor that obstructs electrical insulation with the oxygen pump element and the oxygen concentration battery element, or an electrode for taking out the heating resistor, it is possible to accurately control and measure the current and voltage, thereby improving the air-fuel ratio. It has the great effect of being able to measure very accurately, being easy to manufacture, and having excellent durability.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing each part constituting the first embodiment of the oxygen sensor of the present invention, Fig. 2 is an overall perspective view of the first embodiment, and Fig. 3 is for explaining its usage condition. FIGS. 4 and 5 are plan views showing the state of the unfired plate-like bodies during the manufacturing process, and FIG. 6 is a perspective view showing the state in which the unfired plate-like bodies are overlapped. DESCRIPTION OF SYMBOLS 1... Oxygen pump element, 2, 5... Oxygen ion conductive solid electrolyte plate, 3, 6... Heat-resistant metal layer, 4
...Oxygen concentration battery element, 7,13'...Intermediate plate-shaped body,
8...Relatively large hole, 9...Relatively small hole, 11
...Top side, 12...Original side.

Claims (1)

[Claims] 1. Two oxygen ion conductive solid electrolyte plates for an oxygen pump element and an oxygen concentration battery element, each having heat-resistant metal layers for electrodes and their lead wires on both sides using thick film technology, are placed in the thickness direction. An intermediate plate-like body, which does not include a heat generating resistor, is sandwiched between a ceramic material and a relatively large hole, and one or more relatively small holes in the thickness direction communicating with the hole on the side of the hole. The tip side and the base side are separated by lamination and integral sintering, and the tip side has a flat enclosed chamber and the chamber has a vertical width equal to the thickness of the chamber and is exposed to the outside world. A communication hole is formed for communication, and oxygen permeable walls of an oxygen pump element or an oxygen concentration battery element are formed on both walls in the thickness direction of the chamber, to which a voltage is applied or taken out from the source side via a lead wire. An oxygen sensor characterized by: