JPH0714878Y2 - Limiting current type oxygen concentration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a limiting current type oxygen concentration sensor.

[Conventional technology]

An element used for the limiting current type oxygen concentration sensor, for example, a lean-mixture sensor element is composed of an oxygen ion-permeable solid electrolytic element such as zirconia, an electrode, and a diffusion rate controlling coating (coating layer). When a voltage is applied to the electrode of the element, oxygen ions move from the cathode side to the anode side, which is detected as a current value. This current value increases linearly with the increase of the applied voltage, but the presence of the diffusion-controlling layer suppresses the movement of oxygen ions, saturates the current value, and becomes a value according to the oxygen concentration. Therefore, if the applied voltage is kept constant, the oxygen concentration can be known from the current value. As an example of a document, there is, for example, “Development of Lean Mixture Sensor”, Material No.842054 (October, 1984), Academic Conference of Automotive Engineering Society. JP-A-58-100746 discloses that a cup-shaped solid electrolyte element made of an oxygen-ion permeable metal oxide is provided with a porous thin-film electrode on the inner surface thereof, and the solid electrolyte element has an outer surface on which the plugging is performed. An electrically insulating layer made of a heat-resistant metal oxide is formed in the vicinity of the end except for a predetermined area, and a porous thin film is formed on the outer surface of the solid electrolyte element at the opening of the insulating layer corresponding to the predetermined area. A gas diffusion rate-controlling layer comprising another electrode and a lead wire portion formed on the outer surface of the insulating layer, and the outer surface of the insulating layer, the other electrode and the lead wire portion made of a porous electrically insulating metal oxide. The oxygen concentration sensor covered in 1. is described.

In addition, the applicants of the present invention described in Japanese Utility Model Laid-Open No. 60-179862 are made of a heat-resistant ceramic material except for a predetermined area on the surface of the solid electrolyte element made of an oxygen ion permeable metal oxide on the measured gas side. An electrically insulating layer is formed, a porous thin film electrode is provided on the outer surface of the solid electrolyte element in the opening of the insulating layer corresponding to the predetermined area, and the electrode is electrically connected to the electrode on the outer surface of the insulating layer. Is formed by sintering a conductive metal material and a heat-resistant insulating bonding material on the outer surface of the lead portion, and is bonded to the lead portion through the bonding material. A conductive aggregate formed of, and electrically conducting the aggregate to the electrodes, the electrodes, the lead portion, and the outer surface of the aggregate,
An oxygen concentration sensor covered with a layer of porous electrically insulating ceramic was proposed. Furthermore, the applicants of the present application have taken the advantage of
No. 183857 publication, a cup shape with one end open and the other end closed, having a solid electrolyte element made of an oxygen ion permeable metal oxide, formed on the outer periphery of the solid electrolyte element, the measured gas side thereof. The metal housing is fixed by being electrically insulated from the electrode, and between the housing and the opening side of the solid electrolyte element, an electrical insulating material for maintaining airtightness between the housing and the solid electrolyte element. And a ring-shaped metal holder is inserted into the opening side of the solid electrolyte element, and the inner surface of the holder and the electrode of the solid electrolyte element are electrically connected to each other. Then, there has been proposed an oxygen concentration sensor in which an end portion of the holder separates a conductive portion of the holder from the electrode and the airtight sealing material.

[Problems to be solved by the device]

The above-mentioned conventional oxygen concentration sensor has a problem that the current value is not saturated when used, for example, when the engine is rotating at high speed or under high load, and accurate oxygen concentration cannot be detected. The reason for this is that the portion where the current flows is originally limited to the strip-shaped portion of the closed tip portion of the sensor element with a constant width, but when the temperature of the sensor element rises,
This is because the resistance of the solid electrolyte such as zirconia decreases, so that the current starts flowing through the portions other than the above and the current value is not saturated.

The details will be described below with reference to the drawings. FIG. 2 shows an example of the above-mentioned prior art, for example, a sensor element disclosed in Japanese Patent Laid-Open No. 58-100746. In the figure, 1 is a zirconia element, 2 is an outer electrode, 3 is an inner electrode, 4 is an electric insulating layer, 5 is a gas diffusion rate controlling layer, 6 and 7 are holders, 8 is an electric insulator, and 9 and 10.
Is a ring packing, 11 is a housing, 12 and 13 are lead wires, 14 is an oxygen ion permeable portion, 15 is a shoulder portion, 16 is a space, and 17 is a lead portion.

Conventionally, the electric insulating layer 4 has not been covered up to the entire shoulder 15. The reason for this is that the electric insulating layer 4 is formed by plasma spraying or the like, so if the entire shoulder 15 is sprayed, the work becomes complicated and takes time. In the sensor element of FIG. 2, the housing 11 and the shoulder portion 15 are sealed by the ring packing 10, but if the sealing performance is poor, the gas to be measured enters the space 16. Generally, since the thickness of the solid electrolyte of the shoulder portion 15 is large and the resistance is large, the movement of oxygen ions does not occur. However, when the zirconia element 1 becomes hot, the resistance becomes small and the movement of oxygen ions can occur. . Therefore, at a high temperature, the oxygen in the gas to be measured that has entered the space 16 moves in the direction of the arrow in the figure to move as ions, and a current flows, so the limiting current portion of the voltage-current characteristic curve has a slope and is not horizontal. .

The present invention is intended to solve the above-mentioned problems in the prior art, and its object is to enable a sensor element to exhibit good voltage-current characteristics even under conditions of high temperature and accurately detect oxygen concentration. It is to resist the limiting current type oxygen concentration sensor that can do.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the limiting current type oxygen concentration sensor of the present invention comprises a cylindrical oxygen ion permeable solid electrolyte having one end closed with an inner electrode formed on the inner surface thereof, and a portion contacting the measured gas on the outer surface. Is a sensor element in which an outer electrode is formed on a part of the outer electrode and the other part is covered with an electric insulating layer, wherein the inner electrode is a part opposite to the outer electrode or further a part opposite to the electric insulating layer. It is characterized in that it is provided with a sensor element formed only in a portion including.

The inner electrode may be formed only on the portion opposite to the portion on which the outer electrode is formed, or may be formed only on the portion including the portion on the opposite side of the electrically insulating layer. However, it must not be formed in other parts.

Examples of the method for forming the outer and inner electrodes on desired portions include a method of forming a non-formed portion by using a masking material and then forming by a plating method, or a method of removing unnecessary portions of the formed electrode. Conventional methods can be used.

[Action]

Due to the above structure, in the sensor element of the present invention, the movement of oxygen ions occurs only between the outer electrode and the inner electrode on the opposite side, and the shoulder portion of the sensor element does not move even at a high temperature as in the conventional case. Since there is no movement of oxygen ions, good voltage-current characteristics are exhibited even at high temperatures.

〔Example〕

The invention will be described in more detail in the following examples. The present invention is not limited to the following embodiments.

FIG. 1 is a sectional view of a sensor element of an embodiment of the oxygen concentration sensor of the present invention. The numbers in the figure have the same meanings as defined in FIG. As is clear from comparing FIG. 1 and FIG. 2, in the sensor element of the present invention, the shoulder
Since the inner electrode 3 is not formed on the portion on the opposite side of the lead portion 17 formed on the electrode 15 without the electric insulating layer 4, the movement of oxygen ions in the shoulder portion 15 does not occur even at high temperature. Instead, as shown in the voltage-current characteristic curve of FIG. 3, a clear limiting current portion (horizontal portion in the figure) is produced as compared with the conventional sensor, and the oxygen concentration can be accurately measured.

[Conventional technology]

Since the limiting current type oxygen concentration sensor of the present invention has the above-mentioned configuration, it is possible to accurately measure the oxygen concentration even under the condition that the temperature of the sensor element becomes high. Therefore, the air-fuel ratio can be accurately controlled regardless of changes in operating conditions such as vehicle operating conditions. Further, since the area of the inner electrode is smaller than that of the conventional oxygen concentration sensor, the amount of expensive electrode material such as platinum used can be reduced, resulting in a resource saving effect.

[Brief description of drawings]

FIG. 1 is a sectional view of a sensor element of an embodiment of the limiting current type oxygen concentration sensor of the present invention, FIG. 2 is a sectional view of a sensor element of an example of a conventional limiting current type oxygen concentration sensor, and FIG. It is a figure which shows the voltage-current characteristic curve of a device and the conventional limiting current type oxygen concentration sensor. In the figure, 1 ... Zirconia element, 2 ... Outer electrode 3, Inner electrode, 4 ... Electrical insulating layer 5 ... Gas diffusion rate-controlling layer, 6, 7 ... Holder 8 ... Electrical insulator, 9, 10 ... Ring packing 11 ... Housing, 12, 13 ... Lead wire 14 ... Oxygen ion permeable part, 15 ... Shoulder part 16 ... Space, 17 ... Lead part

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Masahiro Shibata, 1-1, Showa-cho, Kariya, Aichi Prefecture, Nihon Denso Co., Ltd. (72) Inventor, Masaya Fujimoto, 1-1, Showa-cho, Kariya, Aichi Nihondenso Incorporated (56) Reference JP 59-46548 (JP, A) JP 58-100746 (JP, A) Actual 60-179862 (JP, U) Actual 60-183857 (JP, A) U)

Claims (1)

[Scope of utility model registration request] 1. An inner electrode is formed on the inner surface of a cylindrical oxygen-ion permeable solid electrolyte with one end closed, an outer electrode is formed on a portion of the outer surface which is in contact with the gas to be measured, and the other portion is electrically connected. A sensor element covered with an insulating layer, wherein the inner electrode includes a sensor element formed only in a portion opposite to the outer electrode or further in a portion including a portion opposite to the electric insulating layer. A limiting current type oxygen concentration sensor characterized in that