JPH0676987B2 - Oxygen concentration detector - Google Patents

Description

The present invention relates to an oxygen concentration detector, and more particularly to an electric heater for heating a solid electrolyte element.

In recent automobile engines, the exhaust temperature tends to decrease with the improvement of fuel efficiency. For example, when the exhaust temperature is 300 ° C in idle operation, it becomes 250 ° C at the tip of the solid electrolyte element of the oxygen concentration detector. It is not possible to operate with the oxygen concentration detector of.

Therefore, a detector with a built-in electric heater is adopted. As an electric heater, the applicant has proposed a structure in which a metal heating wire is wrapped around a heat-resistant electric insulating tube such as alumina, and the surface of which is coated with ceramics. Therefore, there is a risk that cracking or breakage may occur due to vibration, impact, etc., and there is a drawback that lead wires and heating wires are likely to break.

Further, as another electric heater, there is one having a structure described in JP-A-55-69048. In this electric heater, a metal heating wire is wound around the outer circumference of a cylindrical ceramic tube, one end of the metal heating wire is connected to a conductive rod inserted in the center hole of the ceramic tube, and the other end is connected to the ceramic tube. It is connected to the conductive layer formed on the upper end.

However, even with such a structure, since the base body of the heater is also made of ceramic, cracks or damages are likely to occur when vibration or impact is applied, which may lead to disconnection of the lead wire or the heating wire. . Moreover, since the conductive rod is only inserted into the center hole of the ceramic tube, the conductive rod and the ceramic tube collide with each other due to vibration or shock, and the ceramic tube easily cracks or breaks. There's a problem.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an oxygen concentration detector provided with an electric heater having high reliability against disconnection or the like without causing cracking or damage. To do.

That is, according to the present invention, a heat-resistant electric insulating layer is coated on the outer circumference of a base made of a metal conductive member to integrally form the electric insulating layer on the base, and an electric heating wire is formed on the outer circumference of the insulating layer. One end of the heating wire is connected to the base end and the other end is connected to a metal terminal member provided on the outer surface of the insulating layer to form an electric heater.

An embodiment of the present invention will be described below. FIG. 1 shows the main part of an oxygen concentration detector, and 1 is a solid electrolyte element made of a cup-shaped oxygen ion conductive metal oxide.
The element 1 is fixed to a housing 2, which has a mounting flange 3. Although not shown in detail, electrodes 4a and 4b are provided on the inside and outside of the element 1, and the outer electrode 4b among them is covered with a porous ceramic protective layer (not shown). The inner electrode 4a and the outer electrode 4b have detection terminals 5a, 5
connected to b.

An upper end of the housing 2 is caulked with a metal tube 6, and a ceramic insulating tube 7 is interposed between the metal tube 6 and the outer detection terminal 5b.

A protective tube 8 is connected to the lower end of the housing 2, and the protective tube 8 covers the element 1 with a gap. A plurality of ventilation holes 9 ... Are opened in the protective tube 8.

An electric heater 10 is attached inside the element 1. The electric heater 10 has a structure as shown in FIG. That is, 11 is a columnar metal conductive member that serves as a base, for example, a nickel pipe, and the nickel pipe 11 has a thickness on the outer peripheral surface.
A heat resistant electric insulating layer 12 having a thickness of about 200 μ is coated, and the heat resistant insulating layer 12 is integrally formed with the nickel layer 12 by this coating. The insulating layer 12 is preferably a ceramic layer such as magnesia alumina spinel (MgAl ₂ O ₄ ). On the outer surface of the insulating layer 12, a strip-shaped heating wire 13 made of Fe—Cr—Al alloy or the like is spirally wound at the tip portion of the Nickel tube 11. Further, a nickel ring 14 as a metal terminal member is fitted on the outside of the insulating image 12 at the rear end portion of the nickel tube 11, and the nickel ring 14 is covered with a ceramic adhesive 15 to form an insulating layer 12. Is stuck to. One end 13a of the heating wire 13 is welded to the tip of the nickel pipe 11 and the other end 13b is
Is welded to the tip of the nickel ring 14. A ceramic coating layer 16 formed by plasma spraying is coated on the outer surfaces of the heating wire 13 and the nickel ring 14 for the purpose of preventing contact with the element 1 and protecting the heating wire 13, and this ceramic coating layer 16 is formed. Are formed of the same material as the insulating layer 12. A nickel plug 17 is fitted on the upper end of the nickel pipe 11, and the nickel plug 17
A nickel wire 18 is connected to.

Such an electric heater 10 is inserted through the upper opening of the solid electrolyte element 1, and a ceramic insulating ring 20 is interposed between the upper surface of the element 1 and the nickel ring 14.
Between the nickel ring 14 and the inner detection terminal 5a, talc material
21 and the ceramic insulating ring 22 are assembled. And the heater terminal is on the upper end of the nickel ring 14.
23 is connected.

The oxygen concentration detector having the above structure detects the stoichiometric air-fuel ratio, and the inside of the element 1 is open to the atmosphere. This is because the inside of the element 1 is conducted to the inside of the metal tube 6 through the gap between the inner surface of the element 1 and the ceramic insulating ring 20, the talc material 21, and the ceramic insulating ring 22, and the inside of the metal tube 6 is open to the atmosphere. It has been done.

In the embodiment having such a configuration, the base 11 of the electric heater 10 is made of a conductive metal material such as a nickel pipe, and thus is extremely strong against vibration and impact. For example, it has been confirmed that the example can withstand an impact of about 3000 G.

Further, the heating wire 13 is heated by passing an electric current between the nickel wire 18 and the nickel ring 14, but in this case, since it also serves as the lead wire of the nickel tube 11 as the base, it is the most deteriorated conventionally. The heat resistance inside the intense heat generating center is improved. From this, the durability of the heater was enhanced. That is, FIG. 3 shows a durability test of the resistance change rate of a conventional one (shown by characteristic A) using an alumina insulator tube as a base and one of the present embodiment (shown by characteristic B) using a nickel tube 11 as a base. The results obtained are shown in Example B of the present example, which shows almost no resistance change after 500 hours even if the temperature of the element 1 is heated to 700 ° C. by energizing 30 W, but the conventional example A is 150 It has been confirmed that after a lapse of time or 200 hours, the resistance sharply increases and the durability is poor.

The oxygen concentration detector of the present invention is not limited to the one that detects the oxygen concentration in the exhaust gas of an internal combustion engine for automobiles, and is applicable to air control of, for example, a blast furnace, and is also used as a sensor for the theoretical air-fuel ratio. The present invention is not limited to this, and can be implemented with a lean sensor.

Further, the solid electrolyte element 1 is not limited to the cup-shaped one,
Therefore, the electric heater 10 is not limited to being inserted in the element 1, and may be arranged in the vicinity of the element 1. Also heating line
The material of 13 is not limited to Fe-Cr-Al alloy, but Nichrome wire, Fe
-It is possible to use any metal heating wire such as a Cr alloy. The base body 11 is not limited to the nickel pipe, but Ni-Cr, Fe-Cr, Fe-Cr-
It may be another heat resistant and oxidation resistant metallic material such as Al and the electrically insulating layer 12 may be another ceramic material such as Al ₂ O ₃ .

As described above, according to the present invention, since the metal conductive member is used as the base of the electric heater, the durability against vibration and shock is improved. Moreover, since the metal conductive member also serves as the lead wire of the heating wire, not only the structure is simplified, but also
Thermal deterioration is less than that of thin lead wires, which prevents problems such as wire breakage. Further, since the outer periphery of the base made of a metal conductive member is coated with the heat-resistant electric insulating layer so that the electric insulating layer is formed integrally with the base, the base and the base are electrically connected to each other even if vibration or shock is applied. There are no collisions with the insulating layer, and hence no damage to the base body and the electric insulating layer occurs, and it is possible to obtain a heater having a long life and high reliability.

[Brief description of drawings]

The drawings show one embodiment of the present invention. FIG. 1 is a sectional view showing the main part of an oxygen concentration detector, FIG. 2 is a sectional view showing its electric heater, and FIG. 3 is a characteristic diagram showing durability. is there. 1 ... Solid electrolyte element, 2 ... Housing, 10 ... Electric heater, 11 ... Metal conductive substrate, 12 ... Heat-resistant electric insulation layer, 13 ... Electric heating wire, 14 ... Metal terminal member, 16 ... ... ceramic coating layer.

(72) Inventor Hiromi Sano 1-1, Showa-cho, Kariya, Aichi Prefecture, Nihon Denso Co., Ltd. (72) Inventor, Masaya Fujimoto, 1-1, Showa-cho, Kariya City, Aichi, Nihondenso Co., Ltd. (72) Inventor Toshitaka Saito 1-1, Showa-cho, Kariya city, Aichi prefecture, Nihon Denso Co., Ltd. (72) Inventor, Michihiro Yamakawa, 1-1, Showa-cho, Kariya city, Aichi prefecture, Nihondenso Co., Ltd.

Claims (1)

[Claims] 1. An oxygen concentration detector comprising: a fixed electrolyte element made of an oxygen ion conductive metal oxide; and an electric heater for heating the element, wherein the electric heater comprises a columnar metal conductive member. The outer periphery of the base body is covered with a heat resistant electric insulation layer to form the electric insulation layer so as to be integrated with the base body, and an electric heating wire is arranged on the outer circumference of the insulation layer. An oxygen concentration detector characterized in that the oxygen concentration detector is connected to the base body and the other end is connected to a metal terminal member provided on the outer periphery of the electric insulating layer.