JPH0521425B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a solid electrolyte type oxygen which is used, for example, to measure the oxygen concentration in exhaust gas and control combustion in automobile engines, heaters, etc. It relates to an oxygen sensor element, that is, a solid electrolyte oxygen sensor using a solid electrolyte plate and a porous electrode, and a method for manufacturing the same, and in particular, to a solid electrolyte oxygen sensor that aims to reduce the power consumption of a heater that heats the oxygen sensor element. The present invention relates to a method of manufacturing an oxygen sensor element of a sensor.

[Background of the invention]

Conventionally, the oxygen sensor element of the solid electrolyte type oxygen sensor that has been put into practical use uses one porous electrode provided with a solid electrolyte plate sandwiched between the gas to be measured (oxygen partial pressure).
P _g ), and the other porous electrode is exposed to a reference gas (oxygen partial pressure P _r ), and the other porous electrode is exposed to P _g
By detecting the difference in P _r as a signal voltage V _s expressed by the Nernst equation (V _s ∝lnP _g /P _r ),
The oxygen concentration of the gas to be measured is measured.

In order to extract this signal voltage _Vs , oxygen ions need to flow through the solid electrolyte plate,
The solid electrolyte plate was partially stabilized with Y ₂ O ₃
When ZrO ₂ is used, the signal voltage cannot be obtained unless the temperature of the oxygen sensor element reaches approximately 500° C. or higher.

For example, combustion control for automobiles uses exhaust gas as the gas to be measured, measures the oxygen concentration in the exhaust gas using the oxygen sensor element, and adjusts the ratio of air and fuel to achieve ideal combustion. It is. By the way, in order to significantly reduce the fuel consumption of an automobile, it is necessary to operate this control system from the time the engine is started. Therefore, the temperature of the oxygen sensor element increases to 500℃ due to heating by exhaust gas.
Until the above temperature is reached, it is necessary to warm the oxygen sensor element with a heater, and even after heating with exhaust gas,
It is necessary to maintain the oxygen sensor element at a constant temperature with high precision using the heater.

Problems with the conventional oxygen sensor element configured as described above will be explained below with reference to the drawings.

FIG. 5 is a schematic vertical cross-sectional view showing a conventional fixed electrolyte type oxygen sensor of an indirectly heated type, and FIG. 6 is a cross-sectional view taken along the - arrow in FIG. This type of solid electrolyte oxygen sensor is described in, for example, Japanese Patent Application Laid-Open Nos. 52-72286 and 1987-130649.

In the figure, 2 is an oxygen sensor element of a solid electrolyte type oxygen sensor (details will be described later) in which a porous electrode is formed at the lower end, and 1 is arranged around the lower end of this oxygen sensor element 2. Heaters wrapped with nichrome wire, platinum wire, etc. installed, 1a, 1b
is an electric wire that supplies power to this heater 1, 15
is a solid electrolyte oxygen sensor element holder, 16
is a fixture that is attached to this element holder 15 and holds the oxygen sensor element 2. The oxygen sensor element 2, as shown _{in FIG .} Porous electrodes 5, 6, and 7 are formed on the surface opposite to this mating surface (for example, formed with platinum paste by screen printing), and each porous electrode 5,
6, 7, signal voltage extraction wiring 5a, 6a, 7
a is connected.

In the solid electrolyte oxygen sensor configured as described above, the porous electrode 7 is exposed to the gas to be measured, and the oxygen in the pores of the porous electrode 6 is used as a reference gas (the oxygen flowing from the porous electrode 6 to 7 is (The amount of oxygen corresponding to
The oxygen concentration of the gas to be measured is measured by taking it out from a, 6a, and 7a.

As described above, the conventional solid electrolyte type oxygen sensor is an indirect heating type in which the oxygen sensor element 2 is heated from the surrounding area by the coiled heater 1, so the heating rate is slow and the heat is transferred to the oxygen sensor. Since the power is not effectively transmitted to the element 2, there is a problem in that the heater 1 consumes a large amount of power. Furthermore, since the heater 1 and the oxygen sensor element 2 are separated from each other, the temperature of the oxygen sensor element 2 changes even if the same power is supplied to the heater 1, making it possible to control the temperature of the oxygen sensor element 2 with high precision. There was also a problem that needed to be further improved: it was not possible to carry out this method, and therefore an error occurred in the measured value of the oxygen concentration.

[Purpose of the invention]

The present invention improves the problems of the prior art as described above, and provides an oxygen sensor of a solid electrolyte type, in which the power consumption of a heater for heating an oxygen sensor element is small, and the temperature of the oxygen sensor element can be controlled with high precision. The object is to provide a center element and a method for easily manufacturing the oxygen sensor element.

[Summary of the invention]

The structure of the oxygen sensor element of the solid electrolyte oxygen sensor according to the present invention is that the oxygen sensor element of the solid electrolyte oxygen sensor uses a solid electrolyte plate mainly composed of partially stabilized ZrO ₂ . 2 solid electrolyte plates are laminated, and a porous electrode to which a signal voltage extraction wiring is connected is arranged on the mating surface and the opposite surface of the mating surface, and a gas introduction hole communicating with the outside is provided on either side of the porous electrode. A _gas introduction chamber having a gas introduction hole communicating with _the gas introduction hole is placed opposite to the porous electrode. The solid electrolyte plate is laminated via an intermediate layer of a metal oxide having a thermal expansion coefficient between the solid electrolyte plate and the insulating layer, and the solid electrolyte plate is heated by the heater, A signal voltage related to the oxygen concentration of the gas to be measured that has flowed into the gas introduction chamber from the gas introduction hole is extracted from the signal voltage extraction wiring.

Further, the structure of the method for manufacturing an oxygen sensor element of a solid electrolyte oxygen sensor according to the present invention is made of partially stabilized ZrO ₂ as a main component, with porous electrodes connected to signal voltage extraction wiring formed on both sides. A green sheet of a first solid electrolyte plate, a green sheet of a second solid electrolyte plate mainly composed of partially stabilized ZrO ₂ and having a porous electrode connected to a signal voltage extraction wiring formed on one side; A heater is formed on one of the abutting surfaces, and a set of two green sheets with an insulating layer mainly composed of Al ₂ O ₃ , each having a gas introduction hole formed therethrough, communicates with the gas introduction hole. A gas introduction chamber with a gas introduction hole is formed.
The solid electrolyte plate and the intermediate green sheet of a metal oxide that reacts with the insulating layer during sintering and whose coefficient of thermal expansion after sintering is between the two, are used to form the two solid sheets. The green sheets of the electrolyte plate are stacked so that the porous electrodes and the green sheets alternate, and the intermediate layer is stacked so that one of the porous electrodes protruding to the outside faces the gas introduction chamber. The green sheets are stacked, and the green sheets of the insulating layer are combined on top of the green sheets of the intermediate layer, with the abutting surfaces facing each other so that the gas introduction holes communicate with each other. It is made by laminating and sintering.

[Embodiments of the invention]

Before entering into the description of the embodiments, basic matters related to the oxygen sensor element of the solid electrolyte type oxygen sensor of the present invention and the manufacturing method thereof will be described.

In order to efficiently heat the oxygen sensor element,
A heater may be built into the oxygen sensor element so that the oxygen sensor element can be directly heated. In order to configure this, first and second solid electrolyte plates (both green sheets) are laminated and a porous electrode is arranged on the mating surface and the opposite surface of the mating surface, and a heater is placed on one side of the laminated solid electrolyte plate (both green sheets). A green sheet containing an insulating layer is provided, and these are sintered to manufacture (details of the manufacturing method will be described later).

By the way, _{Al 2} O ₃ can be mentioned as a material for an insulating layer that has excellent insulation properties at high temperatures.
O ₃ has a different thermal expansion coefficient from ZrO ₂ which is the main component of the solid electrolyte plate. Therefore, Al ₂
When an insulating layer mainly composed of O ₃ is laminated in close contact with a solid electrolyte plate mainly composed of ZrO ₂ , it is possible to prevent stress caused by the difference in thermal expansion between the two during sintering or during use at high temperatures. As a result, the oxygen sensor element may be damaged. Furthermore, since ZrO ₂ and Al ₂ O ₃ hardly react with each other, it is difficult to integrate them by sintering.

Therefore, as a means to solve these problems, in the present invention, the thermal expansion coefficient is different from ZrO ₂ , which is the main component of the solid electrolyte plate, and Al ₂ , which is the main component of the insulating layer.
It is an intermediate value between O ₃ and moreover, during sintering
An intermediate layer that reacts with both ZrO ₂ and Al ₂ O ₃ is interposed. The composition of this intermediate layer is, for example, 6 mol containing 3% wt% Al ₂ O ₃
ZrO ₂ partially stabilized with % Y ₂ O ₃ is good.

Examples will be explained below.

FIG. 1 is a sectional view showing an oxygen sensor element of a solid electrolyte oxygen sensor according to an embodiment of the present invention.

This oxygen sensor element 2A has first and second solid electrolyte plates 3 and 4 (ZrO ₂ partially stabilized with 6 mol% Y ₂ O ₃ ) laminated, and on their mating surfaces and on the opposite surface of this mating surface, Porous electrodes 6, 5, and 7 (formed by screen printing using platinum paste) to which signal voltage extraction wiring is connected are arranged, and a gas introduction hole 9a communicating with the outside is penetrated on one side of the porous electrodes 6, 5, and 7 (formed by screen printing using platinum paste). and the heater 1A
Insulating layers 8a and 8b (formed by screen printing using platinum paste) (Al ₂ O ₃ 90
30wt% Al ₂ O ₃ −53wt% SiO ₂ −17wt% in weight part
The intermediate layer 12 (3 wt% Al ₂ O ₃ containing ZrO ₂ partially stabilized with 6 mol% Y ₂ O ₃ ), and a protective layer 14 (for example, magnesium spinel) is formed on the porous electrode 5 on the other side. It is what it is.

The thermal expansion coefficient of the intermediate layer 12 is 20°.
8.4×10 ^-6 /℃ in the temperature range of ~800℃, and the first and second solid electrolyte plates 3 and 4 (8.8×10 ^-6 /℃ in the above temperature range) and the insulating layers 8a and 8b (the above The temperature range is between 8.0×10 ^-6 /℃), so
By interposing this intermediate layer 12 between the second solid electrolyte plate 4 and the insulating layer 8b, stress due to the difference in thermal expansion is alleviated, and during sintering (the manufacturing method will be described later) or during use. Even when the oxygen sensor element 2A is heated to about 800° C. by the heater 1A, the oxygen sensor element 2A is not damaged. Further, since the intermediate layer 12 reacts with both the solid electrolyte plate 4 and the insulating layer 8b, the adhesion between the solid electrolyte plate 4, the intermediate layer 12, and the insulating layer 8b is good, and the oxygen sensor element 2A can be easily baked together. tied.

The oxygen sensor element 2A of the solid electrolyte oxygen sensor configured as described above is exposed to the gas to be measured.
When turned ON, the heater 1A is energized until the temperature of the gas to be measured reaches the preset 800°C, the oxygen sensor element 2A is effectively heated by the heater 1A, and the gas is introduced from the gas introduction hole 9a. room 10
The oxygen concentration of the gas to be measured flowing into the gas can be easily and accurately measured regardless of the temperature of the gas to be measured.

The effects of the oxygen sensor element 2A of this embodiment described above will be explained using FIG. 2.

FIG. 2 is a heater heating characteristic diagram of the solid electrolyte oxygen sensor according to FIG. 1. As is clear from this figure 2, the temperature of the oxygen sensor element 2A is set to 800°C.
The power consumption required to heat up to ℃ is approximately 10W, which is approximately 1/10 of the approximately 100W required for the conventional indirectly heated solid electrolyte oxygen sensor shown in Figure 5.
decreases to

In addition, since the heater 1A and the oxygen sensor element 2A are integrated without any gaps, the oxygen sensor element 2A
The accuracy of temperature control in A is improved from ±20°C to ±5°C, which also has the effect of improving the accuracy of oxygen concentration measurement by about 4 times. Furthermore, by using the solid electrolyte oxygen sensor of this example for combustion control in an automobile engine, combustion control can be performed with high precision from the time the engine is started, reducing fuel consumption by approximately 10% compared to conventional methods. There is an advantage.

Although the oxygen sensor element 2A of this example used ZrO ₂ partially stabilized with 6 mol% Y ₂ O ₃ as the solid electrolyte plates 3 and 4, the composition of the solid electrolyte plates is not limited to this. ZrO ₂ partially stabilized with 4-8 mol% Y ₂ O ₃ or 4-8 mol % CaO, etc.
It may be.

Furthermore, the composition of the insulating layers 8a and 8b is Al ₂ O ₃ 90
30wt% Al ₂ O ₃ −53wt% SiO ₂ −17wt% in weight part
The auxiliary agent is not limited to one in which 10 parts by weight of MgO is added, and the auxiliary agent may be other than Al ₂ O ₃ −SiO ₂ −MgO type, for example, Al ₂ O ₃ −SiO ₂ −CaO type. Alternatively, Al ₂ O ₃ alone may be used as long as the particle size is made fine to approximate the sintering temperature of the solid electrolyte plate and the amount of sintering shrinkage is matched to that of the solid electrolyte plate.

Moreover, the intermediate layer 12 contains 3wt% Al ₂ O ₃ ,
The amount of Al ₂ O ₃ added is not limited to ZrO ₃ partially stabilized with 6 mol% Y ₂ O ₃ and has an allowable range. This will be explained using FIG.

FIG. 3 is a thermal expansion characteristic diagram showing the relationship between the amount of Al ₂ O ₃ added and the coefficient of thermal expansion of the intermediate layer in FIG. 1. In this Figure 3, the amount of Al ₂ O ₃ added is
When it is less than 1.5wt%, the thermal expansion coefficient becomes large and approaches the value of the solid electrolyte plate 4, and the adhesion between the intermediate layer and the insulating layer 8b becomes poor.On the other hand, when it is more than 4wt%, the thermal expansion coefficient becomes large and approaches the value of the solid electrolyte plate 4. As the coefficient becomes smaller, the insulation layer 8
Even if the value of b is approached and an intermediate layer is interposed, the effect of relieving thermal stress is reduced, so the amount of Al ₂ O ₃ added is preferably 1.5 to 4 wt%.

Furthermore, the material of the intermediate layer may be any metal oxide as long as it reacts with the solid electrolyte plate 4 and the insulating layer 8b during sintering and has a coefficient of thermal expansion between the two after sintering. For example, Al ₂ O ₃ −
It may also be SiO ₂ based or TiO based.

Further, in this embodiment, the protective layer 14 was formed on the porous electrode 5 extending outward, but this protective layer 14 may not be provided. However, if it is present, it will prevent the porous electrode 5 from peeling off due to the adhesion of dust or the collision of exhaust gas, which has the advantage of extending the life of the porous electrode 5, that is, the life of the oxygen sensor element 2A. .

Next, an embodiment of a method for manufacturing the oxygen sensor element 2A of the solid electrolyte oxygen sensor shown in FIG. 1 will be described with reference to FIG. 4.

FIG. 4 is a manufacturing process diagram of a method for manufacturing an oxygen sensor element of a solid electrolyte type oxygen sensor according to an embodiment of the present invention. In FIG. 4, the same parts as in FIG. 1 are denoted by the same numbers.

ZrO ₂ powder partially stabilized with 6molY ₂ O ₃ is made into a slurry by adding organic binders, plasticizers, organic solvents, etc., and from this slurry is made into plate-shaped green sheets (thickness: 0.25 mm) and cut it into a predetermined size.A platinum paste made by making a paste of platinum powder with an organic solvent was printed on both sides of the green sheet of the first fixed electrolyte plate 3 using a screen printing method. Porous electrodes 5 and 6 with signal voltage extraction wirings 5a and 6a are formed. Similarly, a green sheet of the second solid electrolyte plate 4 having the same material and the same dimensions as the green sheet of the first fixed electrolyte plate 3 was manufactured, and one side of this green sheet was made of the same material as the porous electrodes 5 and 6. , a porous electrode 7 with a signal voltage extraction wiring 7a is formed by the same method, and on this porous electrode 7,
The core that fits into the gas introduction chamber 10 is filled with organic matter 13.
(Organic material that burns at about 300°C below the sintering temperature, such as ethyl cellulose) is formed by screen printing (a film may also be adhered).

30wt% Al ₂ O ₃ −53wt% SiO ₂ − in 90 parts by weight _of Al ₂ O 3
Mix 10 parts by weight of auxiliary agent of 17wt% MgO,
A green sheet (thickness: 0.15 mm) was manufactured using the same method used to manufacture the green sheet of the solid electrolyte plate 3, and this was cut to the same size as the green sheet, and gas introduction holes 9a were drilled through it. One green sheet of the insulating layer 8b is prepared, and a platinum paste prepared by making a paste of platinum powder in an organic solvent is printed on the abutting surface 11b of the green sheet using a screen printing method to form the heater 1A. Similarly, a gas introduction hole 9a is located at a position opposite to the gas introduction hole 9a.
One green sheet of the insulating layer 8a having the same dimensions as the green sheet of the insulating layer 8b (butting surface 11 of this green sheet)
A (without heater) is created.

In addition, a green sheet (0.25 mm thick) was produced using the same method as described above by mixing 3 wt% Al ₂ O ₃ powder and ZrO ₂ powder partially stabilized with 6 mol Y ₂ O ₃ .
This is cut into the same size as the green sheet of the first solid electrolyte plate 3, and a gas introduction chamber 10 having a gas introduction hole 9b (perforated at a position opposite to the gas introduction hole 9a) is provided in the middle. A layer 12 green sheet is created.

Among the five green sheets prepared in this way, the green sheets of the first and second solid electrolyte plates 3 and 4 on which the porous electrodes 5, 6, and 7 were formed were used to form the porous electrodes and the green sheets. The green sheets of the intermediate layer 12 are stacked alternately, and then the green sheets of the intermediate layer 12 are stacked so that the porous electrodes 7 protruding outside face the gas introduction chamber 10, and then the gas is placed on top of the green sheets. Both abutment surfaces 11a,
A pair of green sheets of the insulating layers 8a and 8b, which are combined with the green sheets 11b facing each other, are stacked with the green sheet of the insulating layer 8b facing downward.

The laminated material was bonded together using a hot press under the conditions of 120℃ x 80Kgf/cm ² and then heated at 1500℃ x
Sintered in the atmosphere for 2hr. The organic layer 13 was burned at a temperature of about 300°C. Thereafter, magnesium spinel was thermally sprayed onto the porous electrode 5 exposed to the outside to form a protective layer 14, and the desired oxygen sensor element 2A was obtained.

According to the method of manufacturing the oxygen sensor element of the fixed electrolyte type oxygen sensor of the present embodiment described above, the solid electrolyte plates 3 and 4 shown in FIGS. Then, a set of two insulating layers 8a, 8 with a heater 1A formed on the abutting surface 11b is formed.
b are laminated and sintered, there is no need to separately install the heater 1 as in the conventional indirectly heated solid electrolyte oxygen sensor shown in FIG. 5, and the solid electrolyte oxygen sensor The manufacturing of the heater 1A is facilitated, and there is no risk of the heater 1A breaking during the manufacturing process.

In this embodiment, the organic layer 13 is formed on the porous electrode 7 of the green sheet of the second solid electrolyte plate 4.
It is not necessary to provide the core 3. However, by providing this, the deformation of the gas introduction chamber 10 of the green sheet of the intermediate layer 12 during stacking is completely prevented, so that the porous electrode 7 with which the gas to be measured flowing into the gas introduction chamber 10 comes into contact during use is This has the advantage of ensuring the largest effective area.

〔Effect of the invention〕

As described above in detail, the present invention provides an oxygen sensor element of a solid electrolyte type oxygen sensor in which the power consumption of the heater for heating the oxygen sensor element is small and the temperature of the oxygen sensor element can be controlled with high precision. , it is possible to provide a method for easily manufacturing this oxygen sensor element.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an oxygen sensor element of a solid electrolyte oxygen sensor according to an embodiment of the present invention, FIG. 2 is a heater heating characteristic diagram of the solid electrolyte oxygen sensor according to FIG. The figure is a thermal expansion characteristic diagram showing the relationship between the amount of Al ₂ O ₃ added and the thermal expansion coefficient of the intermediate layer in Figure 1, and Figure 4 is a solid electrolyte type oxygen sensor according to an embodiment of the present invention. FIG. 5 is a manufacturing process diagram of the manufacturing method of the oxygen sensor element of the indirectly heated type.
FIG. 6 is a schematic vertical cross-sectional view showing a conventional solid electrolyte oxygen sensor, and is a cross-sectional view taken along the - arrow in FIG. 1A...Heater, 2A...Oxygen sensor element, 3
...First solid electrolyte plate, 4... Second solid electrolyte plate, 5, 6, 7... Porous electrode, 5a, 6a,
7a... Signal voltage extraction wiring, 8a, 8b... Insulating layer, 9a, 9b... Gas introduction hole, 10... Gas introduction chamber, 12... Intermediate layer.

Claims (1)

[Claims] 1. In an oxygen sensor element of a solid electrolyte oxygen sensor using a solid electrolyte plate mainly composed of partially stabilized ZrO ₂ , a first and a second solid electrolyte plate are laminated, On either side of the mating surface and the opposite surface of this mating surface, a porous electrode to which a signal voltage extraction wiring is connected is arranged.
An insulating layer mainly composed of Al ₂ O ₃ with a built-in heater and a gas introduction hole that communicates with the outside is bored through it, and a gas introduction chamber that has a gas introduction hole that communicates with the gas introduction hole. via an intermediate layer of a metal oxide whose thermal expansion coefficient is between the solid electrolyte plate and the insulating layer, which is provided opposite to the porous electrode;
The solid electrolyte plate is laminated, and the solid electrolyte plate is heated by the heater, and a signal voltage related to the oxygen concentration of the gas to be measured flowing into the gas introduction chamber from the gas introduction hole is extracted from the signal voltage extraction wiring. An oxygen sensor element of a solid electrolyte oxygen sensor characterized by: 2. The oxygen sensor element of the solid electrolyte oxygen sensor according to claim 1, wherein the intermediate layer is a partially stabilized ZrO ₂ intermediate layer containing 1.5 to 4 wt% Al ₂ O ₃ . 3 A green sheet of the first solid electrolyte plate mainly composed of partially stabilized ZrO ₂ , which has porous electrodes connected to the signal voltage extraction wiring formed on both sides, and a porous electrode to which the signal voltage extraction wiring is connected. A green sheet of a second solid electrolyte plate mainly composed of partially stabilized ZrO ₂ with an electrode formed on one side and a heater formed on one of the abutted surfaces, with a gas introduction hole drilled through it. A set of two green sheets with an insulating layer mainly composed of Al ₂ O ₃ and the solid electrolyte formed during sintering to form a gas introduction chamber with a gas introduction hole that communicates with the gas introduction hole. The green sheet of the two solid electrolyte plates is formed by using a green sheet as an intermediate layer of a metal oxide that reacts with the plate and the insulating layer and whose coefficient of thermal expansion after sintering is between the two. , the porous electrodes and the green sheets are stacked alternately, and the green sheets of the intermediate layer are stacked so that one of the porous electrodes protruding to the outside faces the gas introduction chamber; Further, on top of the green sheet of the intermediate layer, a pair of green sheets of the insulating layer, which are combined with the abutting surfaces facing each other, are laminated and sintered so that the gas introduction holes communicate with each other. A method for manufacturing an oxygen sensor element of a solid electrolyte oxygen sensor, characterized by: