JPH0755765A - Thin film laminated air-fuel ratio sensor - Google Patents

Abstract

PURPOSE:To provide a thin film laminated air-fuel ratio sensor. CONSTITUTION:A first electrode 2 is formed on a porous board 1, and first solid electrolyte 3, a third electrode 4, a second solid electrolyte 5, a fourth electrode 6 are sequentially laminated in a predetermined disposition thereon in such a manner that the electrodes are formed of platinum having porous and gas permeable properties and the electrolytes are oxygen ion conductive solid electrolytes having dense and no gas permeable properties. A sensor element having an oxygen concentration battery type theoretical air-fuel ratio sensor part formed of the electrode 2, the electrolyte 3 and the electrode 4 on the substrate 1 and an oxygen pump cell formed of the electrode 4, the electrolyte 5 and the electrode 6 to be integrally formed is provided. Accordingly, its performance is improved, and its size can be remarkably reduced.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a thin film laminated air-fuel ratio sensor,
More specifically, the present invention relates to a thin film laminated air-fuel ratio sensor that can be made extremely small and has excellent performance.

[0002]

2. Description of the Related Art Various types of air-fuel ratio sensors are used. One of them is an air-fuel ratio sensor using an oxygen sensor. This air-fuel ratio sensor is widely used, for example, as an air-fuel ratio sensor for controlling an automobile engine.
By the way, the oxygen sensor used in the air-fuel ratio sensor is mainly a resistance change type oxygen sensor using a resistance change of an oxide semiconductor, an oxygen concentration battery type oxygen sensor using a solid electrolyte, and an oxygen pump type oxygen sensor ( (Including those in the research and development stage and those already in practical use). The features of the three types of oxygen sensors will be described below.

The resistance change type oxygen sensor utilizing the resistance change of the oxide semiconductor includes TiO ₂ , Nb ₂ O ₅ and SnO _2.
Using n-type semiconductors such as CoO, CoO _1-x M
Some use p-type semiconductors such as g _x . In the resistance change type oxygen sensor, the resistance of the oxide semiconductor changes according to the following expression (I) according to the change in oxygen partial pressure. R = P _o ^{1 / n} (I) [In the formula (I), R: resistance of oxide semiconductor P _o : partial pressure of oxygen n: +4 to +6 for p-type semiconductor, −4 for n-type semiconductor
Indicates -6. ]

When the vehicle is running, the oxygen partial pressure suddenly changes within the range of 10 ^−0.2 to 10 ⁻³⁰ atm at the point where the excess air ratio λ = 1. Therefore, when the excess air ratio λ = 1, the resistance of the oxide semiconductor changes abruptly by 3 to 4 digits as the oxygen partial pressure changes.
Due to this sudden change characteristic, the resistance change type oxygen sensor is used as a theoretical air-fuel ratio detection sensor.

On the other hand, in the oxygen concentration battery type oxygen sensor using a solid electrolyte, the sensor element is made of, for example, zirconia solid electrolyte and has a cylindrical shape with one end closed, and the oxygen content on the exhaust side and the atmosphere side is reduced. The change in pressure (difference in oxygen partial pressure) is detected as an electromotive force as in the following equation (II). E = RT / 4FlnPo ′ / Po (II) [In the formula (II), R: gas constant T: absolute temperature F: Faraday constant P _o ′: oxygen partial pressure on the cathode side P _o : oxygen partial pressure on the anode side Represent. ]

Therefore, in the oxygen concentration cell type oxygen sensor,
When the vehicle is running, an electromotive force within the range of 0 to 1 V is generated as the oxygen partial pressure suddenly changes at the excess air ratio λ = 1. It is detected as the fuel ratio (excess air ratio λ = 1).

The oxygen pump type oxygen sensor is an oxygen sensor of a type which measures the conductivity of oxygen ions of an electrolyte by utilizing an electrochemical pumping action, and is further classified into the following three types depending on the difference in basic constitution. . (A) An oxygen pump cell used as an O ₂ monitor. (B) In which an oxygen pump cell is used with a leaking pore. (C) An oxygen pump cell used as an O ₂ monitor and with leaking pores.

Three types of methods are known as methods for detecting the oxygen concentration in an oxygen pump type oxygen sensor.
The first detection method is a method of measuring oxygen concentration by pumping time, the second detection method is a method of measuring oxygen concentration by limiting current, and the third detection method is a method of measuring oxygen concentration by voltage when a constant current is applied. Is the way to do it. Therefore, since the oxygen pump type oxygen sensor can measure the oxygen concentration in a wide range, this type of oxygen sensor is particularly used as a wide-range air-fuel ratio sensor.

As the theoretical air-fuel ratio sensor, conventionally, a zirconia oxygen concentration cell type sensor and a TiO ₂ resistance change type oxygen sensor have been widely used. Both of these sensors have a characteristic (so-called Z characteristic) in which the output (electromotive force and resistance) suddenly changes in accordance with a large change in the parallel oxygen partial pressure at the theoretical air-fuel ratio. By comparing with an appropriate reference value (voltage value or resistance value) for the sensor, it can be easily determined whether the air-fuel ratio is in the lean region or the rich region.

In the case of a theoretical air-fuel ratio sensor of the zirconia oxygen concentration battery type, the difference in electromotive force between sensor solids and the temperature dependence of electromotive force are small. Therefore, even if the sensor is replaced with another sensor of the same type, or the reference voltage is fixed and used when the exhaust temperature changes when the sensor is attached to the exhaust system of the vehicle, the theoretical air-fuel ratio is It has an excellent property that it can be detected with high accuracy. By having such properties, it is very easy to use for controlling the air-fuel ratio of an automobile engine that also uses a three-way catalyst.
The zirconia oxygen concentration battery type theoretical air-fuel ratio sensor is most widely used for the above-mentioned application.

In the case of a TiO ₂ resistance change type oxygen sensor, since the resistance of the TiO ₂ resistor as a whole changes according to the oxygen partial pressure of the atmosphere, a reference oxygen partial pressure is required when measuring the oxygen concentration. Not. Therefore, the TiO2 resistance change type oxygen sensor does not require a reference electrode or a gas introduction path to the reference electrode, and has a simple structure and can be miniaturized. Therefore, it is gradually used for controlling the air-fuel ratio of an automobile engine. It's starting to happen.

On the other hand, a zirconia limiting current type air-fuel ratio sensor is widely used as a broadband air-fuel ratio sensor. This sensor has the excellent property that the temperature dependence of the sensor electromotive force and the output current is small, and is extremely easy to use. Therefore, it is the most widely used among various range air-fuel ratio sensors.

[0013]

As described above, the conventional sensor, for example, the zirconia oxygen concentration battery type theoretical air-fuel ratio sensor has excellent characteristics, but on the other hand, it has a large problem as exemplified below. It is necessary to measure the theoretical air-fuel ratio with an accuracy of about ± 0.1% with one air-fuel ratio sensor. Further, when the full range air-fuel ratio sensor is added to the theoretical air-fuel ratio sensor, it is necessary to measure the full range air-fuel ratio with an accuracy of about ± 1%. It is necessary to be able to accurately detect the air-fuel ratio immediately after the engine is started. In order to improve the fuel efficiency of the vehicle, it is necessary to minimize the power consumption during sensor operation. A simple structure is required to reduce the cost.

Exhaust regulations for automobiles in the United States, Europe and Japan are becoming stricter year by year, and not only the improvement of the engine of automobiles and the purification performance of exhaust gas purifying catalysts but also the air-fuel ratio sensor have strict requirements. The demands have come to be met, and it has become difficult to deal with the problem only by making small improvements to the conventional technology.

That is, (a) In order to improve the environmental destruction occurring on a global scale, a vehicle engine is desired to have low fuel consumption, a small amount of harmful components emitted, and a high output when necessary. It is rare. For that purpose, it is necessary to precisely control the air-fuel ratio of the engine to the stoichiometric air-fuel ratio. Further, it is more preferable to set the air-fuel ratio of the engine not only to the stoichiometric air-fuel ratio but also to the optimum air-fuel ratio from the lean region to the rich region according to the running state of the vehicle. In order to faithfully control the air-fuel ratio so that it will be the air-fuel ratio set as described above, precise detection of the air-fuel ratio by the air-fuel ratio sensor and feedback control of the air-fuel ratio based on this value are indispensable. Therefore, it is required to accurately detect the stoichiometric air-fuel ratio. Further, in addition to the stoichiometric air-fuel ratio, it is more preferable that the whole region including not only the lean region but also the rich region can be measured.

(B) In the conventional air-fuel ratio sensor, the hydrocarbon (HC) emission amount at the time of cold start of the engine is the amount of hydrocarbon (H) immediately after the engine start before the sensor becomes operable.
C) Emissions account for a large proportion. The hydrocarbon emission amount is closely related to whether or not the fuel amount is increased when the engine is started. Therefore, in order to reduce the amount of hydrocarbon emissions, it is required to rapidly operate the air-fuel ratio sensor immediately after the engine is started in order to optimize the amount of fuel increase when the engine is started. Further, the exhaust gas is treated with an exhaust gas purifying catalyst in order to purify the harmful components discharged. A sensor that can accurately detect the stoichiometric air-fuel ratio is required to fully bring out the purification performance, and the function of the stoichiometric air-fuel ratio and, in addition, a function that can accurately detect a wide range of air-fuel ratios is required as a function of the air-fuel ratio sensor. ing.

However, in order to operate the air-fuel ratio sensor, it is necessary to bring the air-fuel ratio sensor (particularly its air-fuel ratio detecting portion) to a temperature (about 700 ° C.) suitable for operation,
Rapid actuation heating of the sensor is required for rapid operation. However, in general, the rapid temperature rise of the air-fuel ratio sensor is likely to lead to damage or characteristic deterioration due to an increase in thermal strain of each part of the sensor. Therefore, it is necessary to downsize the air-fuel ratio sensor in order to suppress the increase of the thermal strain and reduce the adverse effects thereof.

However, in the case of the zirconia limiting current type air-fuel ratio sensor, the theoretical air-fuel ratio can be detected with high accuracy, and in addition, in order to measure the entire lean region and rich region, both the positive and negative electrodes are hermetically sealed. It is necessary to supply a high concentration of oxygen (air) to the electrode on the side that is kept separated and is not exposed to exhaust gas. Therefore, a passage for introducing air (outside air) for that purpose must be provided from the outside of the sensor to the air-fuel ratio detecting section. Therefore, as the sensor element, a tubular (cup-shaped) sensor element whose one end is closed is usually used. However, there is a limit to the miniaturization of the element as described above, no matter how small the element is.

(C) If the power consumption for heating the air-fuel ratio sensor is large, the power supply for heating such as the generator and the battery must be increased more than ever before, which causes deterioration of fuel consumption. become. Therefore, in order to improve fuel economy, it is necessary and effective to reduce the power consumption of the air-fuel ratio sensor and further improve the function of the sensor.

By the way, the conventional zirconia oxygen concentration battery type theoretical air-fuel ratio sensor requires the reference electrode as described above in order to detect the theoretical air-fuel ratio, and an air introduction mechanism and oxygen are introduced into the theoretical air-fuel ratio sensor. It is necessary to provide a mechanism for generating However, the theoretical air-fuel ratio sensor of the type in which air is introduced from the outside air into the sensor has a complicated and large structure because the size of the air introduction passage is large, and its manufacture is very difficult. Further, since the size is large, heat dissipation loss is also large, and power consumption for heating the air-fuel ratio sensor is large. Further, since the size is large, thermal distortion is likely to occur, rapid heating is not possible, and inevitably the starting time of the stoichiometric air-fuel ratio sensor becomes long. Therefore, since the stoichiometric air-fuel ratio sensor consumes a large amount of power, it adversely affects the fuel efficiency of the vehicle, and since the starting time is long, it cannot contribute to the reduction of hydrocarbon emission immediately after the cold start of the vehicle. .

The conventional zirconia oxygen concentration battery type theoretical air-fuel ratio sensor having a mechanism for generating oxygen in the theoretical air-fuel ratio sensor also has a complicated and large structure in order to add an oxygen generating mechanism. It has the same problem as the stoichiometric air-fuel ratio sensor having a mechanism.

Even in the conventional zirconia limiting current type oxygen sensor, in order to detect the overall air-fuel ratio, it is necessary to introduce air into the air-fuel ratio sensor or to form a reference electrode having an oxygen generating function. That is, with an air-fuel ratio sensor that does not have these means, it is possible to measure only in the lean region, but even in the rich region, a bivalent function characteristic in which a current close to the lean region flows appears. It becomes impossible to determine whether the air-fuel ratio is high or not, and the effective air-fuel ratio cannot be measured in the rich region.

In order to overcome the above problems, however, the lean region air-fuel ratio sensor is provided with a means for discriminating between rich and lean, separately from the means for detecting the air-fuel ratio in the lean region.
It is necessary to add a means for detecting the air-fuel ratio in the rich region and a means for an oxygen pump for supplying oxygen gas constituted by an electrochemical cell.

On the other hand, the full-range air-fuel ratio sensor of the type in which air is introduced from the outside into the air-fuel ratio sensor basically has the capability of detecting the full-range air-fuel ratio with high accuracy. However, this type of global air-fuel ratio sensor has a complicated and large structure in which the size of the air introduction passage is large, and has the same problems as the zirconia oxygen concentration battery type theoretical air-fuel ratio sensor.

The present invention has been made in order to solve the problems in the above-mentioned conventional stoichiometric air-fuel ratio sensor, and the first object thereof is to provide a conventional oxygen concentration such as a small change in electromotive force due to temperature change. A small, high-performance thin-film laminated oxygen concentration battery type that inherits all the excellent properties of a battery-type theoretical air-fuel ratio sensor (for example, a zirconia oxygen concentration battery type theoretical air-fuel ratio sensor) and does not require a passage for introducing air. A theoretical air-fuel ratio sensor (for example, a zirconia oxygen concentration battery type theoretical air-fuel ratio sensor) is provided.

A second object of the present invention is, in addition to the oxygen concentration battery type theoretical air-fuel ratio sensor, excellent heat resistance and stability,
Moreover, it has a feature that the temperature dependence of the sensor output is small, and does not require a passage for introducing air, and has a limiting current type full-range air-fuel ratio sensor having air-fuel ratio detection and measurement performance from the lean region to the rich region (for example, The present invention is to provide a thin film laminated air-fuel ratio sensor that has a zirconia limiting current type full-range air-fuel ratio sensor) and also has a theoretical air-fuel detection unit integrated with it and can be made extremely small in principle in principle.

[0027]

That is, in a thin film laminated air-fuel ratio sensor [referred to as (i)] of the first invention, a first electrode is formed on a porous substrate, and a first electrode is formed on the first electrode. The first solid electrolyte and the third electrode are sequentially stacked, and the first solid electrolyte is the first
The first electrode including the circumference of the electrode is covered, the third electrode covers the first solid electrolyte including the circumference of the first solid electrolyte, and the second solid electrolyte and the fourth electrode are further covered on the third electrode. The second solid electrolyte and the fourth electrode are sequentially stacked,
The first electrode, the third electrode, and the fourth electrode are formed by using platinum that is porous and has gas permeability, and the first solid electrolyte and the second solid electrolyte are dense. Is formed using a solid electrolyte of oxygen ion conductivity having no gas permeability, and is composed of a first electrode, a first solid electrolyte and a third electrode on a porous substrate, and has an oxygen concentration cell type theoretical air-fuel ratio. A part that acts as a sensor,
It is characterized in that it has a sensor element which is composed of a third electrode, a second solid electrolyte and a fourth electrode and is integrally formed with a portion which operates as an oxygen pump cell.

In the thin film laminated air-fuel ratio sensor of the first aspect of the invention, a preferred embodiment of the first aspect of the invention in which a limiting current type full range air-fuel ratio sensor portion is further added to the oxygen concentration battery type theoretical air-fuel ratio sensor portion [(ii)] The second electrode is further formed on the porous substrate independently of the first electrode, and the first solid electrolyte and the third electrode are sequentially stacked on the first electrode and the second electrode. The solid electrolyte covers the first electrode and the second electrode including the periphery of the first electrode and the second electrode, the third electrode covers the first solid electrolyte including the periphery of the first solid electrolyte, and the third electrode The second solid electrolyte and the fourth electrode are sequentially stacked on the electrode, and the second solid electrolyte and the fourth electrode are both the third and third electrodes.
The first electrode, the second electrode, the third electrode, and the fourth electrode are arranged so that the peripheral portions of the electrodes are exposed, and the first electrode, the second electrode, the third electrode, and the fourth electrode are formed by using platinum having gas permeability.
The solid electrolyte is formed by using a dense solid electrolyte that does not have gas permeability and has oxygen ion conductivity, and is composed of a first electrode, a first solid electrolyte and a third electrode on a porous substrate. Formula A theoretical air-fuel ratio sensor, a second electrode, a first solid electrolyte and a third electrode on a porous substrate, and a limit current type global air-fuel ratio sensor, a third electrode, a third electrode, The thin-film laminated air-fuel ratio sensor of (i), which has a sensor element that is integrally formed with a portion that is composed of two solid electrolytes and a fourth electrode and that operates as an oxygen pump cell.

In the thin film laminated air-fuel ratio sensor of the first aspect of the present invention, the entire outer surface of the sensor element is covered with a noble metal catalyst (oxidation catalyst) such as a catalytic metal such as platinum, rhodium or palladium.
It is preferable that the coating layer that carries a predetermined amount is used to completely burn the unburned component in the exhaust gas, and the sensor characteristics are improved because it is not affected by the unburned gas. In this case, the type of catalyst, the supported amount, the thickness of the coating layer, and the coating material are appropriately selected and used alone or in combination.

In the thin film laminated air-fuel ratio sensor of the first aspect of the present invention, the portion where the first electrode is in contact with the porous substrate [(i
In i), the portion where the second electrode is in contact with the porous substrate] has an oxygen concentration cell type theoretical air-fuel ratio sensor [(ii In ()), the performance as a limiting current type full range air-fuel ratio sensor] is further obtained, which is preferable.

In the thin-film laminated air-fuel ratio sensor of the first aspect of the present invention, fine and continuous grooves are formed in the portion of the first electrode [(ii) the first electrode and / or the second electrode] in contact with the porous substrate. Are densely arranged, the first electrode [(ii)
Then, the oxygen gas can be uniformly diffused over the entire surface of the first electrode and / or the second electrode], which is preferable. The size, shape, number, etc. of the grooves are appropriately selected.

In the thin-film laminated air-fuel ratio sensor of the first aspect of the present invention, fine and fine passages communicating with each other are provided in the third electrode at a high density, and the third electrode is provided with the outer peripheral portion of the passage network and the outside. It is preferable to provide a passage that connects through the outer peripheral end surface of the third electrode, because excess oxygen gas in the third electrode can be released to the outside. The size, shape, number, etc. of the passages are selected as appropriate.

Fine and communicating grooves are provided at a high density in a portion of the first electrode [(ii) first electrode and / or second electrode] in contact with the porous substrate, and the third electrode has a fine groove. If the passages communicating with each other are provided at a high density, and further, the third electrode is provided with a passage that connects the outer peripheral portion of the passage network and the outside via the outer peripheral end face of the third electrode, It is even better because it has two advantages.

Therefore, in the thin film laminated air-fuel ratio sensor [(i)] and its preferred embodiment (ii) of the first invention,
More preferable embodiments are as follows. (Iii): The thin film laminated air-fuel ratio sensor according to (i) or (ii), wherein the entire outer surface of the sensor element is covered with a coating layer carrying a catalytic metal. (Iv): first electrode [in (ii), first electrode and / or second electrode
Electrodes] are provided in the portion in contact with the porous substrate with fine, high-density communicating grooves (i) to (iii).
) Any one thin film laminated air-fuel ratio sensor. (V): Passages in which fine and fine passages that communicate with each other are provided at high density in the third electrode, and further connect the outer peripheral portion of the passage network and the outside to the third electrode via the outer peripheral end face of the third electrode. A thin film laminated air-fuel ratio sensor according to any one of (i) to (iii). (Vi): first electrode [first electrode and / or second electrode in (ii)]
Electrode] The portion 3 in contact with the porous substrate is provided with high density and fine grooves for communicating with each other, and is provided with high density for fine and mutually communicating passages in the third electrode, and further, for the third electrode, A thin-film laminated air-fuel ratio sensor according to any one of (i) to (iii), wherein a passage is provided to connect the outer peripheral portion of the passage network to the outside via the outer peripheral end surface of the third electrode.

The porous substrate used in the thin film laminated air-fuel ratio sensor of the first aspect of the invention may be formed using a material commonly used in this field, such as alumina. The size and shape of the porous substrate, the porosity, and the porosity are optimally selected.
If desired, the sensor element may be provided with a heating means such as a heater at an appropriate position on the porous substrate.

The solid electrolyte used in the thin film laminated air-fuel ratio sensor of the first aspect of the present invention may be formed of a suitable size and shape by using conventional materials such as zirconia and yttria alone or in combination. it can.

The electrodes used in the thin film laminated air-fuel ratio sensor of the first aspect of the invention may be formed by a conventional method such as a printing method using a suitable noble metal paste such as platinum paste, or by vapor deposition or the like. Good. The size, shape and thickness of the electrodes are selected appropriately.

The thin film laminated air-fuel ratio sensor of the first invention is
It may be provided with auxiliary means conventionally used in this field for actual use, for example, voltage applying means, voltage or current measuring means, heater heating means and the like.

In the thin film laminated air-fuel ratio sensor [referred to as (vii)] of the second invention, the first electrode is formed on the porous substrate, and the first solid electrolyte and the third electrode are formed on the first electrode. Sequentially stacked, the first solid electrolyte covers the first electrode including the periphery of the first electrode, the third electrode covers the first solid electrolyte including the periphery of the first solid electrolyte, and further the third electrode The second solid electrolyte having an opening above is formed with a space provided between the second solid electrolyte and the third solid electrolyte of the second solid electrolyte.
A fourth electrode is formed on the surface facing the electrode, and a fifth electrode is formed on the surface of the second solid electrolyte opposite to the surface facing the third electrode, and the second solid electrolyte and the fifth electrode are both third electrodes. The first electrode, the third electrode, the fourth electrode, and the fifth electrode are arranged so that the peripheral portions of the electrodes are exposed, and are made of platinum that is porous and has gas permeability. The solid electrolyte is formed by using a dense solid electrolyte that does not have gas permeability and has oxygen ion conductivity, and is composed of a first electrode, a first solid electrolyte and a third electrode on a porous substrate. Formula: A sensor element having a portion that operates as a theoretical air-fuel ratio sensor and a portion that includes a fourth electrode, a second solid electrolyte and a fifth electrode and that operates as an oxygen pump cell are integrally formed. To do.

In the thin film laminated air-fuel ratio sensor of the second aspect of the invention, a preferred embodiment of the first aspect of the invention in which a limiting current type full range air-fuel ratio sensor portion is further added to the oxygen concentration battery type theoretical air-fuel ratio sensor portion [(viii) The second electrode is further formed on the porous substrate independently of the first electrode, and the first solid electrolyte and the third electrode are sequentially stacked on the first electrode and the second electrode. The solid electrolyte covers the first electrode and the second electrode including the periphery of the first electrode and the second electrode, the third electrode covers the first solid electrolyte including the periphery of the first solid electrolyte, and the third electrode A second solid electrolyte having an opening on the electrode is formed with a space provided between the second solid electrolyte and the first solid electrolyte,
A fourth electrode is formed on the surface of the second solid electrolyte facing the third electrode, and a fifth electrode is formed on the surface of the second solid electrolyte opposite to the surface facing the third electrode. The fifth electrode is disposed so that the peripheral portion of the third electrode is exposed, and the first electrode, the second electrode, the third electrode, the fourth electrode, and the fifth electrode.
The electrodes are formed of platinum that is porous and has gas permeability, and the first solid electrolyte and the second solid electrolyte are formed of dense and non-gas permeable oxygen ion conductive solid electrolyte, A portion composed of the first electrode, the first solid electrolyte and the third electrode on the porous substrate, which operates as an oxygen concentration battery type theoretical air-fuel ratio sensor, and the second electrode, the first solid electrolyte and the first electrode on the porous substrate. A part composed of three electrodes, which operates as a limiting current type global air-fuel ratio sensor, and a part composed of a fourth electrode, a second solid electrolyte and a fifth electrode, which operates as an oxygen pump cell are integrally formed. It is characterized by having a sensor element.

In the thin film laminated air-fuel ratio sensor of the second aspect of the invention, unlike the thin film laminated air-fuel ratio sensor of the first aspect of the invention, the second solid electrolyte having an opening above the third electrode is
A space is provided between the first solid electrolyte and the first solid electrolyte.
The size (volume) and shape of the space are appropriately selected. or,
The space may be filled with a suitable porous material, for example foam ceramic. When the amount of oxygen gas supplied into the space by the oxygen pump cell composed of the fourth electrode, the second solid electrolyte and the fifth electrode is excessive, oxygen gas is detected from the opening of the second solid electrolyte. Since it is released to the outside of the device, the partial pressure of oxygen gas in the space is always optimally controlled.

The size of the opening provided in the second solid electrolyte,
The shape and the number are appropriately selected so that a predetermined performance of the sensor element can be obtained. A pinhole, for example, can be used as the opening.

In the thin film laminated air-fuel ratio sensor [(vii)] and its preferred embodiment (viii) of the second invention,
More preferable embodiments are as follows. (Ix) The thin film laminated air-fuel ratio sensor according to (vii) or (viii), wherein the entire outer surface of the sensor element is covered with a coating layer carrying a catalytic metal. (X) Fine and communicating grooves are provided at high density in a portion of the first electrode [the first electrode and / or the second electrode in (viii) that is in contact with the porous substrate] (vii) or ( ix) Any one of the thin film laminated air-fuel ratio sensors. (Xi) The third electrodes are provided with minute and fine passages that communicate with each other at high density, and further, the third electrodes are provided with passages that connect the outer peripheral portion of the passage network and the outside through the outer peripheral end face of the third electrode. The thin film laminated air-fuel ratio sensor according to any one of (vii) to (ix). (Xii) Fine and dense grooves for communicating with each other are provided in a portion of the first electrode [the first electrode and / or the second electrode in (viii)] that is in contact with the porous substrate, and the third electrode has fine grooves. Passages communicating with each other are provided at high density, and further, passages are provided in the third electrode for connecting the outer peripheral portion of the passage network and the outside through the outer peripheral end face of the third electrode (vii). A thin film laminated air-fuel ratio sensor according to any one of (ix).

With respect to the other constituent elements and auxiliary means in the thin film laminated air-fuel ratio sensor of the second aspect of the present invention, the same things as the constituent elements of the thin film laminated air-fuel ratio sensor of the first aspect of the invention can be said.

[0045]

In the thin film laminated air-fuel ratio sensor of the present invention, as in the case of the conventional zirconia theoretical air-fuel ratio sensor, one electrode is provided with a passage for introducing air (outside air) for maintaining a high oxygen concentration. Rather than naturally supplying air to the sensor element by diffusion, oxygen is dissociated from water vapor and carbon dioxide contained in a large amount in the vehicle engine combustion exhaust gas, and oxygen ions are forcibly supplied by the oxygen pump action. .
Further, in the sensor of the present invention, since the oxygen concentration battery cell is laminated under the oxygen pump cell on the porous substrate by the thin film method, rapid heating, rapid temperature rising and rapid operation are possible with low power consumption. The stoichiometric air-fuel ratio can be measured with high accuracy. In addition, in the thin film laminated air-fuel ratio sensor of the present invention, in a mode in which a limiting current cell is further added in addition to the oxygen concentration battery cell, it is possible to measure the entire range air-fuel ratio in addition to the theoretical air-fuel ratio.

[0046]

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

Embodiment 1 (First Invention) FIG. 1 shows a sensor according to Embodiment 1 of the present invention. The structure of this sensor is, for example, a porous substrate 1 made of alumina or the like.
A first electrode 2, a first solid electrolyte 3 and a third electrode 4 are sequentially stacked on top of each other. The first solid electrolyte 3 covers the first electrode 2 including the periphery of the first electrode 2, and the third electrode 4 is The first solid electrolyte 3 including the periphery of the first solid electrolyte 3 is covered and hidden, and the second solid electrolyte 5 and the fourth electrode 6 are sequentially stacked on the third electrode 4, and the second solid electrolyte 5 and the fourth solid electrolyte 4 are formed. The electrodes 6 are both arranged so that the peripheral portion of the third electrode 4 is exposed, and the first electrode 2, the third electrode 4, and the fourth electrode 6 are made of porous and gas-permeable platinum (platinum). Formed by a printing method of applying a paste), a first solid electrolyte 3 and a second solid electrolyte 3
The solid electrolyte 5 was formed by using a dense solid electrolyte having oxygen ion conductivity and having no gas permeability (using zirconia).

A heater 7 was provided on the back surface of the porous substrate 1. The heater 7 is connected to the heater heating means 8.
The heater 7 is preferably made of a noble metal such as platinum, rhodium or palladium, or an alloy thereof, or a heat-resistant conductive material such as SiC, W, Re or Mo, and platinum was used in this example.

Further, as shown in FIG. 1, a voltage applying means 9 for applying a positive voltage to the third electrode 4 with respect to the fourth electrode 6 is provided. Reference numeral 10 is a voltage measuring means for measuring the potential difference (voltage) of the third electrode 4 with respect to the first electrode 2.

When a positive voltage is applied to the third electrode 4 with respect to the fourth electrode 6, in this portion including the second solid electrolyte 5, the oxygen pumping action causes the side from the fourth electrode 6 side to the third electrode 4 side. Oxygen ions are transported to. In this case, under a lean air-fuel ratio atmosphere, oxygen remaining in the atmosphere is supplied to the fourth electrode 6 by gas diffusion. On the other hand, in a rich air-fuel ratio atmosphere, since oxygen is not sufficiently present in the atmosphere, water vapor and carbon dioxide supplied from the atmosphere to the fourth electrode 6 by gas diffusion are dissociated at the fourth electrode 6 to generate oxygen ions. Oxygen ions are produced and transported as in the previous case. The transported oxygen ions are converted into oxygen gas at the interface between the second solid electrolyte 5 and the third electrode 4. Thus, in the porous third electrode 4, the excess oxygen state is always maintained regardless of the lean air-fuel ratio atmosphere or the rich air-fuel ratio atmosphere.

The portion composed of the first electrode 2, the first solid electrolyte 3 and the third electrode 4 functions as an oxygen concentration cell type air-fuel ratio detecting section, and the stoichiometric air-fuel ratio can be measured from the electromotive force. In this state, the electromotive force characteristics of the oxygen concentration cell type air-fuel ratio detection section were measured using the excess air ratio in the combustion exhaust gas around the sensor as a parameter, and FIG. 2 was obtained.

Since the third electrode 4 is a porous body and its outer peripheral portion communicates with the outside of the sensor, when excessive oxygen is supplied to the third electrode 4, the third electrode 4 is excessively discharged from the outer peripheral portion to the outside. Since no oxygen is discharged, it does not hinder the measurement. Further, the oxygen gas in the first electrode 2 is discharged into the porous substrate 1.

Second Embodiment (First Invention) FIG. 3 shows a sensor according to a second embodiment of the present invention. The present sensor is the same as the sensor of the first embodiment except that fine and communicating grooves 11 are provided at a high density in a portion of the first electrode 2 which is in contact with the porous substrate 1. Although the theoretical air-fuel ratio sensor uses a platinum electrode, platinum does not always have sufficient durability against repeated oxidation / reduction, so the surface of the sensor is covered with a porous layer to prevent the gas reaching the electrode surface from the atmosphere. When the deterioration is suppressed by limiting the diffusion amount, long-term stability can be easily obtained. Therefore, it is an effective method to reduce the diffusion amount of gas by using the porous substrate 1 having a large diffusion resistance, but on the other hand, a portion (ineffective portion) where oxygen gas is difficult to be supplied in the surface of the first electrode 2 That is, a long transient response time occurs. Then, the electromotive force of the normal portion having a short transient response time and the electromotive force of the abnormal portion having a long transient response time affect each other, resulting in a characteristic that the change of the electromotive force is slow as a whole. This is unsuitable as a sensor for air-fuel ratio control. The present embodiment provides an effective solution to this problem.

The groove 11 has the function of facilitating the diffusion of oxygen gas within the surface of the first electrode 2 and suppressing the oxygen concentration distribution within the surface to a low level. As a result, when the porous substrate 1 having a large diffusion resistance is used, the generation of a portion (ineffective portion) where oxygen gas is difficult to be supplied in the plane of the first electrode 2, that is, an abnormal portion having a long transient response time is generated. It can be suppressed, and the transient response time in the electrode plane can be made uniform. Therefore, it is possible to prevent the characteristics unsuitable for an air-fuel ratio control sensor in which the change in electromotive force is slow as a whole, and to obtain good durability and very good results for long-term stability. Came to be.

FIG. 4 is a plan view of the first electrode 2 of the sensor of FIG. In this example, the grooves 11 are provided in a grid pattern at predetermined intervals.

Embodiment 3 (First Invention) FIG. 5 shows a sensor according to Embodiment 3 of the present invention. In this sensor, fine and fine passages 12 that communicate with each other are provided in the third electrode 4 at a high density. Further, the third electrode 4 is provided with the outer peripheral portion of the passage network and the outside through the outer peripheral end face of the third electrode 4. Passage 1 to connect
The sensor is the same as that of the first embodiment except that 3 is provided.

If the pressure inside the third electrode 4 becomes higher than the outside pressure by the action of the oxygen pump, excess oxygen gas is discharged to the outside through the fine passages 13 and 14 described above, so that the second electrode 4 is discharged. The rise in internal pressure is suppressed.

FIG. 6 shows the AA of the third electrode 4 of the sensor of FIG.
Figure 3 shows a plan view along the line. In this example, the passages 12 are provided in a grid pattern at predetermined intervals, and the passages 13 are provided in the outer peripheral portion of the passage 12 in the vertical and horizontal directions so as to connect the outer peripheral portion of the passage 12 to the outside.

Embodiment 4 (First Invention) FIG. 7 shows a sensor according to Embodiment 4 of the present invention. Similar to the sensor of the second embodiment, this sensor is provided with fine and dense grooves 11 communicating with each other in the portion of the first electrode 2 which is in contact with the porous substrate 1, and like the sensor of the third embodiment. Passages 12 that are fine and communicate with each other are provided at high density in the third electrode 4, and further, a passage that connects the outer peripheral portion of the passage network and the outside to the third electrode 4 via the outer peripheral end face of the third electrode 4. The sensor is the same as that of the first embodiment except that 13 is provided.

Therefore, this sensor has both the advantages of the sensor of the second embodiment and the advantages of the sensor of the third embodiment.

FIG. 8 is a plan view of the first electrode 2 of the sensor of FIG. In this example, the grooves 11 are provided in a grid pattern at predetermined intervals.
9 is a plan view of the third electrode 4 of the sensor of FIG. 7 taken along the line AA. In this example, the passages 12 are provided in a lattice pattern at a predetermined interval, and the passages 13 are provided in the outer peripheral portion of the passage 12 in the vertical and horizontal directions so as to connect the outer peripheral portion of the passage 12 to the outside.

Embodiment 5 (First Invention) FIG. 10 shows a sensor according to Embodiment 5 of the present invention. The structure of this sensor is such that a first electrode 2 and a first electrode are arranged in parallel on a porous substrate 1 (for example, unevenness on the surface of the porous substrate has a peak interval of 1 μm or more) made of alumina or the like. The second electrode 143, the first solid electrolyte 3 and the third electrode 4 are sequentially stacked, and the first solid electrolyte 3 includes the first electrode 2 and the second solid electrolyte 3.
The first electrode 2 and the second electrode 14 including the periphery of the electrode 14 are covered, and the third electrode 4 covers the first solid electrolyte 3 including the periphery of the first solid electrolyte 3, and the third electrode 4 is further covered. The second solid electrolyte 5 and the fourth electrode 6 are sequentially stacked on top of the second
Both the solid electrolyte 5 and the fourth electrode 6 are arranged so that the peripheral portion of the third electrode 4 is exposed, and the first electrode 2 and the second electrode 1
4, the third electrode 4 and the fourth electrode 6 are formed by using platinum that is porous and has gas permeability (for example, is formed by a printing method of applying a platinum paste), and the first solid electrolyte 3
The second solid electrolyte 5 is formed by using a dense solid electrolyte having no gas permeability and having oxygen ion conductivity (for example, zirconia).

A heater 7 was provided on the back side of the porous substrate 1. The heater 7 is connected to the heater heating means 8.
The heater 7 is preferably made of a noble metal such as platinum, rhodium or palladium, or an alloy thereof, or a heat-resistant conductive material such as SiC, W, Re or Mo, and platinum was used in this example.

Further, as shown in FIG. 10, a voltage applying means 15 for applying a positive voltage to the third electrode 4 with respect to the fourth electrode 6 is provided. Further, the voltage applying means 16 for applying a positive voltage to the third electrode 4 with respect to the second electrode 14 is provided. Reference numeral 17 is a current measuring means for measuring the flowing current. Further, the voltage measuring means 10 for measuring the electromotive force generated between the first electrode 2 and the third electrode 4 is provided.

When a positive voltage is applied to the third electrode 4 with respect to the fourth electrode 6, the oxygen pumping action causes the fourth electrode 6 to the third electrode 4 in this portion including the second solid electrolyte 5.
Oxygen ions are transported to the side. In this case, under a lean air-fuel ratio atmosphere, oxygen gas remaining in the exhaust gas, and further steam and carbon dioxide contained in the exhaust gas are dissociated at the fourth electrode 6 to generate oxygen ions. On the other hand, in a rich air-fuel ratio atmosphere, oxygen is not sufficiently present in the atmosphere, so that water vapor and carbon dioxide contained in the exhaust gas are not contained in the fourth electrode 6
Is dissociated to generate oxygen ions. The generated oxygen ions are ion-conducted in the second solid electrolyte 5 and are transported to the third electrode 4, and are converted into oxygen gas at the interface between the second solid electrolyte 5 and the third electrode 4. In this way, in the porous third electrode 4, the excess oxygen state is always maintained regardless of the lean air-fuel ratio atmosphere or the rich atmosphere.

Second electrode 14, first solid electrolyte 3 and third
The portion including the electrode 4 operates as a limiting current type global air-fuel ratio sensor, and the air-fuel ratio can be measured from the limiting current. In this state, using the excess air ratio in the combustion exhaust gas around the sensor as a parameter, the current-voltage characteristics of the limiting current type global air-fuel ratio sensor were measured, and FIG. 11 was obtained. Further, FIG. 12 shows a current measured by applying an applied voltage shown by a chain line in FIG.

On the other hand, the portion consisting of the first electrode 2, the first solid electrolyte 3 and the third electrode 4 operates as an oxygen concentration cell type theoretical air-fuel ratio sensor, and the theoretical air-fuel ratio should be measured from the sudden change characteristic of electromotive force. You can Therefore, when the electromotive force characteristic of the oxygen concentration battery type theoretical air-fuel ratio sensor was measured using the excess air ratio in the combustion exhaust gas around the sensor as a parameter, the same relation as shown in FIG. 2 was obtained.

The characteristics of the air-fuel ratio sensor according to the prior art are shown in FIGS. 18 and 19 for comparison with the air-fuel ratio sensor portion of the sensor of the fifth embodiment. 18 is a diagram corresponding to FIG. 11, and FIG. 19 is a diagram corresponding to FIG. As is clear from the comparison of FIG. 18 with FIG. 11 and FIG. 19 with FIG.
In the air-fuel ratio sensor of the prior art, the limiting current characteristic appears in the third quadrant in an atmosphere in which the excess air ratio is smaller than 1 (that is, fuel rich), whereas the air-fuel ratio sensor portion of the sensor of the present invention. Then it appears in the 4th quadrant.

As a result, the conventional product has a positive applied voltage in an atmosphere in which the excess air ratio is greater than 1 (that is, fuel lean) and a negative applied voltage in an atmosphere in which the excess air ratio is less than 1 (ie, fuel rich). While it was necessary to switch the polarity of the applied voltage, the air-fuel ratio sensor portion of the present embodiment does not need to switch the polarity because the positive applied voltage is always required.

Therefore, in the product of this embodiment, it is not necessary to additionally provide means for detecting whether the detection atmosphere is fuel lean or fuel rich.

Further, since it is no longer necessary to switch the polarity of the applied voltage, in the product of this embodiment, the generation of a noise-like output signal component due to the switching is also eliminated.

The air-fuel ratio sensor portion of the sensor of this embodiment does not have an oxygen introducing portion from the outside air unlike the conventional full-range air-fuel ratio sensor, but as described above, it functions as an oxygen pump on the third electrode 4. Oxygen is supplied by the addition of an electrochemical cell to perform an operation equivalent to that of the conventional air-fuel ratio sensor of the prior art.

Embodiment 6 (First Invention) FIG. 13 shows a sensor according to Embodiment 6 of the present invention. This sensor was implemented except that fine and communicating grooves 11 were provided at high density in the portions of the first electrode 2 and the second electrode 14 in contact with the porous substrate 1 as in the sensor of Example 2. Same as the sensor of Example 5. In the oxygen sensor, when the current per unit area of the electrode (that is, the current density) is increased, not only the effect of the electrode resistance increases and the initial characteristics are easily deteriorated, but also the long-term stability becomes difficult to obtain. Therefore, it is an effective method to reduce the current density by using the porous substrate 1 having a large diffusion resistance, but on the other hand, the first electrode 2 and the second electrode 14 are used.
Since the number of portions (ineffective portions) to which oxygen gas is not supplied increases in the plane, the electrode resistance is likely to increase, and it is difficult to obtain a sufficient effect. The present embodiment provides an effective solution to this problem.

The groove 11 has an action of facilitating the diffusion of oxygen gas within the planes of the first electrode 2 and the second electrode 14 and suppressing the oxygen concentration distribution within the plane to a low level. Accordingly, when the porous substrate 1 having a large diffusion resistance is used, the first electrode 2 and the second electrode 2
It is possible to suppress an increase in the portion of the surface of the electrode 14 to which oxygen gas is not supplied, and prevent an increase in electrode resistance. Therefore, in combination with the decrease in current density, good initial characteristics are obtained, and very good results are obtained for long-term stability.

The plan view of the groove 11 provided in the first electrode 2 and the second electrode 14 of the sensor of the sixth embodiment is the same as FIG. In this example, the grooves 11 are provided in a grid pattern at predetermined intervals.

Embodiment 7 (First Invention) FIG. 14 shows a sensor according to Embodiment 7 of the present invention. In this sensor, fine passages 12 which communicate with each other are provided in the third electrode 4 at high density as in the sensor of the third embodiment.
The sensor is the same as the sensor of the fifth embodiment except that a passage 13 is provided to connect the outer peripheral portion of the passage network to the outside through the outer peripheral end surface of the third electrode 4.

Since the third electrode 4 is a porous body and its outer peripheral portion communicates with the outside of the sensor, excess oxygen is supplied to the third electrode 4 by the action of the oxygen pump, and the inside of the third electrode 4 is supplied. If the pressure is higher than the external pressure, the above-mentioned fine passage 1
Excessive oxygen gas is discharged to the outside through the passage 2 and the passage 13, so that the increase in the pressure inside the third electrode 4 is suppressed, which does not hinder the measurement. Further, the oxygen gas in the first electrode 2 and the second electrode 14 is discharged into the porous substrate 1.

The plan view of the third electrode 4 of the sensor of Example 7 taken along the line AA is the same as FIG. In this example, the passage 12
Are provided in a grid pattern at a predetermined interval, and the passages 13 are provided in the outer peripheral portion of the passage 12 in the vertical and horizontal directions so as to connect the outer peripheral portion of the passage 12 to the outside.

Embodiment 8 (First Invention) FIG. 15 shows a sensor according to Embodiment 8 of the present invention. This sensor is similar to the sensor of the sixth embodiment in that the first electrode 2 and the second electrode 14
The grooves 11 communicating with each other in high density are provided in the portion in contact with the porous substrate 1 of the above, and the passages 12 communicating with each other in the third electrode 4 are dense as in the sensor of the seventh embodiment. Same as the sensor of the fifth embodiment except that the third electrode 4 is provided with a passage 13 that connects the outer peripheral portion of the passage network and the outside through the outer peripheral end surface of the third electrode 4. Is.

Therefore, the present sensor has both the advantages of the sensor of the sixth embodiment and the advantages of the sensor of the seventh embodiment.

The plan view of the first electrode 2 and the second electrode 14 of the sensor of Example 8 is the same as FIG. In this example, the grooves 11 are provided in a grid pattern at predetermined intervals. The plan view of the third electrode 4 of the sensor of Example 8 taken along the line AA is the same as FIG. In this example, the passages 12 are provided in a lattice pattern at a predetermined interval, and the passages 13 are provided in the outer peripheral portion of the passage 12 in the vertical and horizontal directions so as to connect the outer peripheral portion of the passage 12 to the outside.

Embodiment 9 (First Invention) FIG. 16 shows a sensor according to Embodiment 9 of the present invention. This sensor is the same as the sensor of Example 5 except that the entire sensor element is covered with the coating layer 18 supporting the catalytic metal. For example, platinum may be used as the catalyst metal and alumina may be used as the material of the coating layer. The reason why the coating layer 18 supporting the catalytic metal is provided will be described below.

The output current characteristics of the limiting current type all-three air-fuel ratio sensor and the electromotive force characteristics of the oxygen concentration battery type theoretical air-fuel ratio sensor are greatly affected by the unburned gas component in the exhaust gas of the automobile, which is the subject.

In an automobile engine, however, gasoline and air are mixed and burned in each cylinder, but in that case, the concentration of the unburned gas component generated in each cylinder may be different. For example, assuming that the first cylinder has a large amount of H ₂ as an unburned gas component after combustion, and the other cylinders have a large amount of HC gas, the sensor is placed at a position greatly affected by the first cylinder having a large amount of unburned H ₂ gas component. If attached, it is expected that the output current will increase in the limiting current type global air-fuel ratio sensor and the electromotive force sudden change point will move to the lean side in the oxygen concentration battery type theoretical air-fuel ratio sensor. Furthermore, if the sensor is installed at a position affected by another cylinder,
The output current becomes smaller in the limiting current type full range air-fuel ratio sensor, and it is expected that the electromotive force sudden change point moves to the rich side in the oxygen concentration battery type theoretical air-fuel ratio sensor.

Since the sensor characteristics change depending on the unburned gas component reaching the sensor, it is necessary to minimize the influence of the unburned gas component. As a countermeasure against this, it is effective to coat the entire sensor element with a coating layer carrying a catalytic metal such as platinum, rhodium or palladium. If there is such a coating layer carrying a catalytic metal, the unburned gas components reaching the sensor element surface are completely burned in the coating layer by the action of the catalyst. Therefore, the test gas supplied to the sensor element does not contain unburned component gas, which is effective as a method for stabilizing the sensor output characteristics.

When the coating layer 18 supporting the catalytic metal is provided, the material, the porosity, the thickness of the coating layer, the type of the catalyst, and the loading amount are appropriately selected so that the desired performance can be obtained. To do.

Embodiment 10 (Second Invention) FIG. 17 shows a sensor according to Embodiment 10 of the present invention. In the thin film laminated air-fuel ratio sensor of the second aspect of the present invention, unlike the thin film laminated air-fuel ratio sensor of the first aspect of the present invention, there is a space in the sensor element. That is, in the sensor of the present embodiment, the second electrode having the opening 19 (pinhole) on the third electrode 4 is used.
The solid electrolyte 5 is formed with a space 20 provided between the solid electrolyte 5 and the first solid electrolyte 3, and the third electrode 4 of the second solid electrolyte 5 is formed.
The fourth electrode 21 is formed on the side, and the fifth electrode 22 is formed on the side of the second solid electrolyte 5 opposite to the third electrode 4. The other structure is similar to that of the sensor of the ninth embodiment.
The function of the space 20 will be described below.

In the sensor of this embodiment, if the pressure in the space 20 increases due to the oxygen pumping action of the oxygen pump cell,
Excessive oxygen gas is discharged to the outside of the sensor element through the opening 19, so that the oxygen gas pressure in the space 20 is reduced, so that the atmosphere in the vicinity of the third electrode 4 is maintained at a constant oxygen atmosphere. The three electrodes 4 act as a reference oxygen electrode.

As described above, in the sensor of the present invention, since the oxygen pump cell that creates a reference electrode corresponding to the conventional atmospheric reference electrode and the oxygen concentration battery type theoretical air-fuel ratio sensor are integrated, the oxygen concentration battery The stoichiometric air-fuel ratio can be detected accurately from the sudden change characteristics of the electromotive force of the theoretical air-fuel ratio sensor. Further, in the mode in which the limiting current type global air-fuel ratio sensor is added in addition to the oxygen concentration battery type theoretical air-fuel ratio sensor, a wide air-fuel ratio from the rich region to the lean region can be detected based on the output current.

[0090]

Since the thin film laminated air-fuel ratio sensor of the present invention has the above-mentioned structure, it has various effects as exemplified below. 1) Since this sensor supplies oxygen to the sensor element by the oxygen pump action, it is not necessary to provide an oxygen introduction part in the sensor element and a part communicating with the outside of the housing is not required. Therefore, the entire sensor can be downsized. 2) Since the sensor element does not need to be provided with an oxygen introducing portion in the sensor element, it is not necessary to form the sensor element into a three-dimensional structure such as a cylindrical shape as in the conventional sensor, and may have a planar configuration. It is suitable for manufacturing by thin film technology. 3) Since this sensor does not require an oxygen introduction part, the airtight structure of the housing becomes simple. 4) This sensor is integrated with a part that dissociates oxygen, a part that acts as an oxygen pump, and a part that operates as an oxygen concentration battery type theoretical air-fuel ratio sensor, and its temperature dependence is small, so it is easy to use. . 5) In the oxygen concentration battery type theoretical air-fuel ratio sensor part of this sensor, the theoretical air-fuel ratio can be accurately measured without performing a complicated operation such as adjusting the reference voltage by temperature. 6) Since this sensor can be miniaturized, the electric power required for heating is small. 7) Since this sensor is manufactured by the thin film method, the thermal strain generated is small and the stability is good even if the temperature is rapidly raised. 8) Since this sensor is manufactured on the porous substrate by the thin film technology, mass productivity is good and cost reduction at the time of manufacturing is possible. 9) Since this sensor can be variously modified, its application range is wide. 10) In the mode in which the portion that operates as the limiting current type global air-fuel ratio sensor is added to this sensor, the limiting current type global air-fuel ratio sensor portion detects the air-fuel ratio from the rich region to the lean region without switching the applied voltage. can do.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an air-fuel ratio sensor according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an electromotive force characteristic of the air-fuel ratio sensor of the first embodiment.

FIG. 3 is an explanatory diagram of an air-fuel ratio sensor according to a second embodiment of the present invention.

FIG. 4 is a plan view of a first electrode of the air-fuel ratio sensor of FIG.

FIG. 5 is an explanatory diagram of an air-fuel ratio sensor according to a third embodiment of the present invention.

6 is a plan view of the third electrode of the air-fuel ratio sensor of FIG. 5, taken along the line AA.

FIG. 7 is an explanatory diagram of an air-fuel ratio sensor according to a fourth embodiment of the present invention.

FIG. 8 is a plan view of a first electrode of the air-fuel ratio sensor of FIG.

9 is a plan view of the third electrode of the air-fuel ratio sensor of FIG. 7, taken along the line AA.

FIG. 10 is an explanatory diagram of an air-fuel ratio sensor according to a fifth embodiment of the present invention.

FIG. 11 is a diagram showing current-voltage characteristics of a limiting current type full range air-fuel ratio sensor portion of an air-fuel ratio sensor of Example 5;

FIG. 12 is a diagram showing a current measured by applying an applied voltage shown by a chain line in FIG. 11 to the air-fuel ratio sensor of Example 5;

FIG. 13 is an explanatory diagram of an air-fuel ratio sensor according to a sixth embodiment of the present invention.

FIG. 14 is an explanatory diagram of an air-fuel ratio sensor according to a seventh embodiment of the present invention.

FIG. 15 is an explanatory diagram of an air-fuel ratio sensor of Example 8 of the present invention.

FIG. 16 is an explanatory diagram of an air-fuel ratio sensor according to a ninth embodiment of the present invention.

FIG. 17 is an explanatory diagram of an air-fuel ratio sensor according to a tenth embodiment of the present invention.

FIG. 18 is a diagram showing current-voltage characteristics of a limiting current type full range air-fuel ratio sensor portion of a conventional air-fuel ratio sensor.

FIG. 19 is a diagram showing a current measured by applying a predetermined applied voltage in the conventional air-fuel ratio sensor.

[Explanation of symbols]

 1 Porous Substrate 2 1st Electrode 3 1st Solid Electrolyte 4 3rd Electrode 5 2nd Solid Electrolyte 6,21 4th Electrode Decomposition 7 Heater 8 Heater Heating Means 9, 15, 16 Voltage Applying Means 10 Voltage Measuring Means 11 Grooves 12, 13 Passage 14 Second electrode 17 Current measuring means 18 Coating layer 19 Opening 20 Space 22 Fifth electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Saji Kei-shi, Aichi-gun, Aichi-gun, Nagakute-cho, Nagachote 1 41 of Yokomichi Yokoido Central Research Institute Co., Ltd. (72) Inventor Shoji Takeuchi, Aichi-gun, Nagakute-cho 1 in 41 Chuo Yokoido Central Research Institute Co., Ltd. (72) Inventor Kozo Usuda 1 in 41, Nagachite Yokoido Aichi District Aichi Prefecture Toyota Central Research Co., Ltd.

Claims (2)

[Claims] 1. A first electrode is formed on a porous substrate, a first solid electrolyte and a third electrode are sequentially stacked on the first electrode, and the first solid electrolyte includes a first electrode including a periphery of the first electrode. 1st electrode is covered, 3rd electrode covers 1st solid electrolyte including the circumference | surroundings of 1st solid electrolyte, 2nd solid electrolyte and 4th electrode are sequentially laminated | stacked on 3rd electrode, 2nd solid The electrolyte and the fourth electrode are both disposed so that the peripheral portion of the third electrode is exposed, and the first electrode, the third electrode, and the fourth electrode are formed of platinum that is porous and has gas permeability. The solid electrolyte and the second solid electrolyte are formed by using a dense, gas-impermeable, oxygen-ion-conducting solid electrolyte, which is composed of a first electrode, a first solid electrolyte, and a third electrode on a porous substrate. That operates as an oxygen concentration battery type theoretical air-fuel ratio sensor When the third electrode is constituted by the second solid electrolyte and a fourth electrode, the thin film stack fuel ratio sensor, characterized in that a portion which operates as an oxygen pump cell having a sensor element made integrally formed. 2. A first electrode is formed on a porous substrate, a first solid electrolyte and a third electrode are sequentially stacked on the first electrode, and the first solid electrolyte includes a first electrode including a periphery of the first electrode. The first electrode covers the first electrode, the third electrode covers the first solid electrolyte including the periphery of the first solid electrolyte, and the second solid electrolyte having an opening on the third electrode is A space is provided between the second solid electrolyte and the third electrode of the second solid electrolyte, and a fourth electrode is formed on the surface of the second solid electrolyte facing the third electrode.
A fifth electrode is formed on the surface opposite to the surface facing the electrode,
The second solid electrolyte and the fifth electrode are both arranged so that the peripheral portion of the third electrode is exposed, and the first electrode, the third electrode, the fourth electrode, and the fifth electrode are made of porous platinum having gas permeability. The first solid electrolyte and the second solid electrolyte are formed by using a dense and oxygen ion conductive solid electrolyte having no gas permeability, and the first electrode and the first solid are formed on the porous substrate. A portion composed of an electrolyte and a third electrode, which operates as an oxygen concentration battery type theoretical air-fuel ratio sensor, and a portion composed of a fourth electrode, a second solid electrolyte and a fifth electrode, which operates as an oxygen pump cell are integrally formed. A thin film laminated air-fuel ratio sensor comprising a formed sensor element.