JPH02306565A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent an insulation drop of an insulator under high temperature while improving heat resistance and foulingproofness together with holding mechanical strength by making the materials of respective members composing the main part the prescribed ones. CONSTITUTION:The cylindrical metal fittings 1 are formed of a material having tensile strength not less than 40kg/mm<2> and thermal conductivity not less than 120W/mk. A long-stem part insulator 2 is formed of ceramics mainly composed of alumina. A corrugation part insulator 3 is formed of a material having thermoconductivity not less than 60W/mk. A thereby formed spark plug has a sufficient strength for mounting while preventing an insulation drop of an insulating part due to high temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spark plug for an internal combustion engine, and particularly to a wide range plug with improved heat resistance and stain resistance.

[Prior Art] Conventionally, as shown in FIG.
a cylindrical metal shell 100 welded to the cylindrical metal shell 1;
It consists of a cylindrical insulator 200 made of nitride ceramic, which is fitted into the insulator 200, and a center electrode 300 which is fitted into the insulator 200. Spark plug B obtained
is proposed. (Japanese Patent Application No. 63-55577,
Japanese Patent Application No. 151153/1983, Japanese Patent Publication No. 55/466
Publication No. 34).

[Problems to be Solved by the Invention] However, the conventional spark plug B has the following drawbacks.

(1) Nitride ceramics (including aluminum nitride)
When Spark Plug B using Insulator 200 is actually installed in a car engine and subjected to a long-term durability test,
Shallow cracks 220 on the insulator surface 210 that are thought to be caused by corona discharge
is dug from the root 230 toward the ignition part side 240, and high voltage leaks along this course 220, making it easy for ignition errors to occur.

(2) Nitride-1 ceramics, as shown in Figure 4 (the insulator in this graph is aluminum nitride),
At high temperatures, electrical conductivity increases (insulation deteriorates)
However, the extension of the corona from the root 230 of the long leg portion 250 of the insulator 200 becomes significant. As a result, the expansion of this corona reaches the firing part side 240 and the normal gap 310
This causes an ignition error.

An object of the present invention is to provide a spark plug for an internal combustion engine that does not cause deterioration of insulation at high temperatures, has excellent heat resistance and stain resistance, and has a wide range.

[Means for Solving the Problems] In order to achieve the above-mentioned problems, the present invention has a cylindrical metal shell, each having a shaft hole, and which is coaxially fitted into the front end side and rear end side of the metal shell. C
In the spark plug for an internal combustion engine, the cylindrical metal shell has a tensile strength of 4.
0kg/mm2"-1 or more, and the thermal conductivity is 12
The long leg insulator is made of a ceramic mainly composed of alumina, and the corrugation insulator has a thermal conductivity of 60 W/mk or more.
A structure made of - materials was adopted.

[Action and effect of invention] The present invention has the following functions and effects.

Since the leg insulator is made of a ceramic insulator mainly composed of alumina, there is little deterioration in insulation even when the leg insulator reaches high temperatures due to heat reception.

In addition, the corrugation insulator has a thermal conductivity of 60 W.
/mk or more, and the metal shell is made of a material with a thermal conductivity of 120 W/mk or more.

Here, the corrugation portion insulator acts as a sink to release the heat received by the leg length portion insulator, and quickly conducts the heat to the metal shell. That is, the long leg insulator near the ignition part loses heat quickly, and the spark plug has excellent heat resistance and stain resistance.

The reason for the numerical limitation is as follows.

If the thermal conductivity of the corrugation portion insulator is less than 60 W/mk, it will not function efficiently as a heat sink for dissipating heat received by the leg length portion insulator. Thermal conductivity of the metal shell is 1
If it is less than 20 W/mk, the heat transmitted to the corrugated insulator cannot be efficiently received or stopped, nor can the received heat be quickly radiated. If the tensile strength of the metal shell is less than 40 kg/mm2, the mechanical strength when installing the spark plug in an internal combustion engine will be poor. Note that each numerical value is a value at room temperature.

[Example] Next, the structure of a spark plug for an internal combustion engine according to the present invention will be explained with reference to FIG.

Spark plug A (equivalent to BPR4EY) has =4- a cylindrical metal shell 1, a leg insulator 2 fitted into the tip side of the cylindrical metal shell 1, and a leg insulator 2 fitted into the rear part of the leg insulator 2. The corrugation part insulator 3 is provided with a central electrode 4 inserted into the shaft hole 21.31 of each insulator 2.3.

The cylindrical metal shell 1 is made of the material shown in FIG. 2, has a tapered surface 11 formed on its inner wall, and fixes the base of the leg insulator 2 via a copper packing 12. Furthermore, an engine mounting screw 13 is threaded on the outer periphery of the cylindrical metal shell 1, and an outer electrode 14 is welded to the tip surface.

The leg insulator 2 (leg length is 20 mm) is made of alumina and has a thermal conductivity of 20 W/mk>.

The rear end of the leg insulator 2 is a convex portion 23 with a conical tapered surface 22.

The corrugation insulator 3 is made of a material shown in FIG. 2, and the shaft hole 31 is formed larger than the shaft hole 21. This corrugated portion insulator 3 is provided with a high melting point glass bonding material 32 at a position slightly closer to the rear end than the tapered surface 11.
It is joined by Note that the corrugation portion insulator 3 may be made of other ceramic materials, heat-resistant plastics, etc. as long as it is an insulator with a thermal conductivity of 60 W/mk or more.

The center electrode 4 consists of an electrode body 41 and a glass sealing material 42.

The electrode main body 41 has a substantially rod-like shape, with a round rod-like tip and a flange-like rear end. This electrode body 41 is made of nickel alloy 43
Copper 44 is sealed inside. The electrode main body 41 is loosely fitted into the shaft hole 21 with the flange-shaped portion being engaged with the tapered surface 22 .

A glass sealing material 42 is filled in the shaft hole 31 to establish electrical continuity between the electrode main body 41 and the center shaft (not shown), and to fix the brim portion.

Next, the effects of spur plug A will be described.

(1) As shown by the arrow 51, the heat received by the leg insulator 2 passes through the copper 44 part of the center electrode 4, and goes to the ■ collar, the corrugation insulator 3, and the metal shell 1 (arrow 52), and ■ the leg length. Insulator 2, copper packing 12, metal shell 1 (arrow 53
), ■ smoothly escapes to the flange, the glass sealing material 42, the corrugation insulator 3, and the metal shell 1 (arrow 54). Therefore, the temperature at the tip of the plug does not rise excessively, and ignition is less likely to occur.

(2) Since the long leg insulator 2, which is exposed to high heat, is made of alumina, there is little deterioration in insulation even in a high temperature environment.

(3) Since the spark plug has a relatively long leg length of the leg insulator 2 of 20 mm, it has excellent stain resistance.

Next, a test for evaluating the Breignion resistance (heat resistance) and staining resistance of this spur plug A will be described.

(1) About the Breignion resistance test 1600cc,
It was installed in a 4-cylinder engine (rotation speed 5000 rpm x 4/4) and the advance angle at which ignition occurred was determined. This test was conducted in three sets each using the combinations shown in FIG.

No. 2, No. 3, No. 5, No. 6 are the products of the present invention. N.

1, No. 4, No. 7 to 9 are non-invention products, NQIO is a conventional product, and Nα11 and No. 12 are reference products.

Invention product No. 2, No. 3, No. 5, N(1
6 has a larger "C" ignition advance angle than that of the same heat value (Nα10) and has excellent bregnition resistance.

(2) Regarding the fouling test, a similar engine was used (environmental temperature -10℃), one cycle was idling for 90 seconds, and 35 km/h speed for 120 seconds, and the insulation resistance was IOM.
The number of cycles at which the Ωmoldiness decreased was determined.

The products of the present invention No. 2, No. 3, N+o, 5., No. 6 had a low thermal value (long leg length of 20 mm), and naturally had excellent stain resistance.

In addition, the number of cycles showing the stain resistance of reference products No. 11 (1111 length part 17 mm) and No. 12 (leg length part 14 mm) is about 5 to 7.

According to each of the above tests, the present invention products Nα2, No3, No.
5.Nα6 has the advantage of excellent stain resistance due to its low heat value, and has been demonstrated to have approximately the same resistance to braking as BPR5EY (leg length 17 mm).

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a spark plug for an internal combustion engine according to the present invention. FIG. 2 is a graph showing the test results of the Breignion resistance test and the staining test. FIG. 3 is an explanatory diagram showing grooves that occur in a conventional spark plug due to insulation deterioration at high temperatures. FIG. 4 is a graph showing the relationship between temperature and electrical conductivity of aluminum nitride.

Claims (1)

[Scope of Claims] 1) A cylindrical metal shell, a leg insulator and a corrugation insulator each having a shaft hole and coaxially fitted into the front end side and rear end side of the metal shell; In the spark plug for an internal combustion engine, the spark plug includes a center electrode inserted through a shaft hole in each of the insulators, wherein the cylindrical metal shell has a tensile strength of 40 kg/mm^2 or more and a thermal conductivity of 40 kg/mm^2 or more. is formed of a material having a thermal conductivity of 120 W/mk or more, the leg insulator is formed of a ceramic mainly composed of alumina, and the corrugation insulator has a thermal conductivity of 60 W/mk.
A spark plug for an internal combustion engine, characterized in that it is formed of a material of K or more.