JPH0298086A - Ring-shaped semiconductor for igniter plug - Google Patents

Abstract

PURPOSE:To intend higher durability when fired under high pressure by setting a ring-shaped semiconductor, used for a gap between a cylindrical metal shell and a center electrode and taper-shaped around the outer periphery of a tip portion, to be a lower resistance value on the inner periphery side than on the outer periphery side. CONSTITUTION:A ring-shaped semiconductor 3 has a carbon-made core rod inserted in the center thereof and given hot-press sintering so that its inner periphery side 3A has a lower resistance value than its outer periphery side 3B. Also, the outer periphery is given a convergently tapered shape to decrease abruptly a resistance value between the inner face and the outer face with nearing the tip. An igniter plug 100 is so constructed that this semiconductor is fitted into a ring gap between a cylindrical metal shell 1 which is convergently taper-shaped around the inner periphery of the tip portion and a center electrode 2 placed at the center thereof. It is thus possible to cause fire discharge intensively at the ring gap 20 to the tip face 31 of an insulator and not to cause the same inside the semiconductor of a higher resistance value, resulting in higher durability.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a semiconductor for a low-voltage discharge type igniter plug used for ignition of jet engines, gas turbine engines, etc. It is concerned with the durability of semiconductors when subjected to

[Prior Art] A low-voltage discharge type igniter plug is a hot-press sintered annular or cylindrical semiconductor device placed in the spark discharge gap (ignition part) between a center electrode and a ground electrode to reduce the discharge voltage. I'm letting you do it. As this annular semiconductor, US Pat. No. 3,558,959 discloses a structure manufactured by hot press sintering using silicon carbide (SiC) and alumina (A 1203 ) as main raw materials. This semiconductor was developed with the aim of improving durability when high-energy spark discharge occurs in high-temperature conditions and fuel-wet conditions.
It has various resistance values.

[Problems to be Solved by the Invention] However, in today's jet engines and gas turbine engines, for safety reasons, the igniter plug is sometimes operated even under high pressure of, for example, 20 kg/cm 2 or more after the engine is operated. The inventor found that under such high pressure, spark discharge from the igniter is likely to occur not only on the tip surface (the eruption portion) of the annular semiconductor but also inside the semiconductor. The occurrence of spark discharge inside the semiconductor accelerates the consumption of the semiconductor 5 and makes it more likely to be damaged.

The purpose of this invention is to use silicon carbide and alumina as the main raw materials, and to create a structure in which these raw materials are hot-press sintered and molded into an annular shape. An object of the present invention is to provide an annular semiconductor for a low-voltage discharge type igniter plug, which has a structure in which the discharge tends to concentrate on the tip surface and is difficult to occur inside the semiconductor.

[Means for Solving the Problems] In order to achieve the above object, the semiconductor of the present invention is a low voltage discharge type igniter plug which has an annular shape in which the outer periphery of the tip is tapered and the inner periphery of the tip is tapered. In an annular semiconductor that is used by being fitted into the tip of an annular gap between a cylindrical metal shell formed in a tapered shape and a center electrode placed at the center, resistance on the inner circumference side is used. A configuration was adopted in which the resistance value was set lower than the resistance value on the outer circumferential side.

[Operation and Effects of the Invention] The electric resistance value between the inner surface and the outer surface of the annular semiconductor is such that when the outer peripheral portion is formed in a tapered shape, the distance between the inner and outer surfaces decreases toward the tip. , the tip becomes smaller.

According to the configuration of the present invention, in the one-circular semiconductor, the resistance value on the inner circumferential side is lower than the resistance value on the outer circumferential side. Therefore, the outer circumferential side, where the resistance value is higher, becomes selectively thinner toward the tip. As a result, the electrical resistance value between the inner surface and the outer surface decreases rapidly toward the tip.

This semiconductor is fitted into the tip of an annular gap between a cylindrical metal shell whose tip has a tapered inner periphery and a center electrode placed at the center of the metal shell to form an Ig → ~ Itaplug. With this configuration, spark discharge occurs intensively at the tip end face of the insulator (ignition part of the igniter plug) having a low resistance value, and is less likely to occur inside the semiconductor having a high resistance value.

[Example] An annular semiconductor for a low voltage discharge type igniter plug according to the present invention will be explained with reference to the drawings.

In FIG. 1, reference numeral 100 indicates a cross section of the tip of a low voltage discharge type igniter plug. 1 is a cylindrical main metal fitting;
The inner periphery of the tip (lower end in the figure) portion 11 is formed into a tapered shape, and the tip is a cylindrical surface 12 with a small diameter (diameter 6.4 ROM) and an axial length of 1.2+nm. The tip of the igniter plug 100 including the cylindrical surface 12 serves as the ground electrode 10. Reference numeral 2 denotes a center electrode, whose tip 21 is formed to have a large diameter (4.0 mm in diameter) and is arranged at the center of the axis of the metal shell 1. 3 is an annular semiconductor according to the present invention, the outer periphery of which is tapered to correspond to the inner periphery of the metal shell, and the inner periphery is dimensioned so that the tip 21 of the center electrode is fitted therein. This semiconductor 3 is fitted into the tip of the annular gap 2A between the metal shell 1 and the center electrode 2. Also, between the two people in this annular gap,
A cylindrical insulator 4 is disposed in contact with the rear end surface of the semiconductor 3.

The tip cylindrical surface 12 of the metal shell and the tip 21 of the center electrode
The annular gap 20 between the two is a spark discharge gap, and the tip surface 31 of the semiconductor 3 is a creeping surface facing this discharge gap. This low voltage discharge type igniter plug 100 is
A voltage of about 2 kilovolts is applied between the ground electrode 10 and the center electrode 2 with the center electrode 2 as the positive electrode, and a high energy discharge is generated in the spark discharge gap.

[Manufactured Samples and Data] The semiconductor 3 according to the present invention was manufactured in the following order.

(1) Silicon carbide 23.6% by weight, alumina 70°8% by weight, 30% silica sol solution 2.9 as a binder
% by weight, magnesium oxide (MgO) 0', 3% by weight,
0.5% by weight of calcium oxide and 1.9% by weight of silicon oxide were added, and further 0.5% of polyvinyl alcohol was added as an organic binder. Distilled water was mixed and kneaded for 3 hours.

(2) After drying, granulate the powder to about 450 microns, and press-mold the powder in a steel press mold at 2t/Cl1l'' to produce an annular press-molded product.

(3) Next, as shown in FIG. 2, this press-molded product 300 is inserted into a carbon press mold 5, and with the carbon core 51 inserted in the center, hot press firing is performed under the following firing conditions concluded.

(a) Heating at a heating rate of 20°C/min, first to 1200°
When the temperature reaches C, pressurize at 150-250k<1/cm2.

(b) Then maintain the temperature at 1850°C for 30 minutes.

(c) After that, gradually cool with air and release the pressure at 1400°C or less.

(4) In the thus fired annular semiconductor 1, the carbon core 51 is fired together with the semiconductor 3 and cannot be easily removed, so it is removed by polishing or the like.

(5) As a result, as shown in Figures 1, 3, and 5, the outer diameter is 10 mm, the inner diameter is 4 + nm, and the length is 10 mm.
It has a cylindrical shape, and is 0.1 to 0.5 mm from the inner wall on the inner peripheral side.
The depth of part 3A is 0.01~0゜2 megaohm, and the other fil! A semiconductor 30 having a resistance value of 2 to 50 megohms in the other parts>3B is obtained.

The cause of this distribution of electrical resistance in the radial direction has not been confirmed, but it is assumed that it is due to a density distribution occurring within the semiconductor during hot press sintering, or to the carburization phenomenon of the carbon used in the core. .

Moreover, the distribution of electrical resistance value in the radial direction is as follows:
This occurs significantly when the mixing ratio of arsenic and alumina is in the range of 50 to 85% by weight of silicon carbide and 50 to 15% by weight of mina.

(6) This semiconductor 30 is polished to a size that can be incorporated into the igniter plug 100 shown in FIG. 1, and as shown in FIG.
．． 5mm semiconductor 3 was manufactured.

This semiconductor 3 was assembled into the igniter plug 100 shown in Fig. 1, and in a space pressurized to a high pressure of 25 kg/Cl112, it was connected to a capacitive discharge type exciter (4 joules of energy) to measure the consumption of the semiconductor due to spark discharge. Shina.

The amount of semiconductor wear was determined by the amount of change in the position of the semiconductor tip surface from the initial stage shown in FIG.

The measurement results of the number of spark discharges and the change ff1L are shown in the graph of FIG.

(3) shows a case where the annular semiconductor 3 of the present invention is used, and the portion 3A at a depth of 0.3 mm from the inner wall on the inner peripheral side is 0.3 mm deep.
1 megohm, outside (other part) 3B is 10
It has a resistance value of mega ohms.

(2) shows the case where a comparative semiconductor product having the same dimensions as (2) and whose entire annular semiconductor has a uniform resistance value of about 1 megohm is used.

As a result, the annular semiconductor 3 of the present invention has much better wear resistance against high-energy spark discharge under high pressure than conventional annular semiconductors, which have uniform electrical resistance values throughout. It is proven that

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of the tip of a low-voltage discharge type igniter plug using the semiconductor of the present invention, FIG.
The figure is a perspective view of an intermediate semiconductor product, Figure 4 is a perspective view of the semiconductor of the present invention, Figure 5 is a sectional view of the tip of an igniter plug in a wear test, and Figure 6 shows the amount of semiconductor wear in a wear test. This is a graph showing. In the diagram 100...Low voltage discharge type igniter plug
・Cylindrical main metal fitting 2... Center electrode 3... Annular semiconductor 4... Insulator

Claims (1)

[Scope of Claims] 1) A cylindrical metal shell having an annular shape with an outer periphery formed in a tapered shape and an inner periphery formed in a tapered shape; It is a semiconductor of a low voltage discharge type igniter plug that is used by being inserted into the tip of the annular gap between the center electrode and the resistance value on the inner circumference side is set lower than the resistance value on the outer circumference side. Characteristic circular semiconductor for igniter plugs.