JPH0233879A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To freely form a long leg portion of a spark plug made of aluminum nitride and noble metal and improve thermal resistance and self cleaning capability thereof by specifying the size and the form of the composing material thereof. CONSTITUTION:A spark plug is composed of aluminum nitride with thermal conductivity of 60W/mk or more as an insulating material and noble metal as an electrode. There is the relationship among the diameter A of the end portion of an insulator, that B of the insulator of a main fitting at the end face thereof, that C of the step portion of the insulator and that M of a screw, that is, A<=2.0mm, B/M<=0.35 and C/M>=0.4. A straight portion 1e of 5mm or less is provided following to a taper portion 1d of the end of a long leg portion. With this configuration, preignition is hardly occurred, the temperature of the insulator is kept required for self-cleaning and thermal conductivity is improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a spark plug for an internal combustion engine, in particular, to improve the heat resistance and heat resistance of the plug by using AIN ceramic having a gold conductivity of 60 W/mK or more as an insulator. This invention relates to a spark plug that improves self-cleaning performance.

<Prior Art> When the insulator material of a spark plug is changed from kAl20s to AIN, the heat resistance (pre-venilasilane property) is improved. This is because the thermal conductivity of AIN is several times better than that of Alx0g. AIN with good thermal conductivity
Although it is thought that the shape of the leg part has an extremely large effect on gray ignition resistance, the effect of this shape has not been sufficiently studied so far.

Problems to be Solved by the Present Invention The present invention expands the degree of freedom in the shape of the leg part by integrally firing the center electrode formed with an insulator using AIN, and improves heat resistance and self-cleaning properties. An object of the present invention is to provide a spark plug having an effective shape.

A feature of the present invention is that in a Subakardewog made by firing an aluminum nitride insulator having a thermal conductivity of at least 60 W/mk or more together with a center electrode made of a noble metal, the tip of the insulator is The diameter is A, the insulator body diameter of the metal shell mounting part is B1, the step diameter of the insulator C and the mounting screw diameter of the metal shell are M, As2, Off, B/M≦0.35, C/ M
This is a spark plug that satisfies ≧0.4, and is a spark plug that has a straight part that is at most 5 m long following the tapered part at the tip of the long leg part.

Effect> Plug preignition occurs mainly at the tip of the insulator. Considering the flow of heat in an insulator, heat is received from the combustion gas at the tip, flows toward the step, and is emitted to the metal shell. The flow of heat toward this step, especially when an insulator with good heat conductivity is used, is greatly influenced by the shape of the long leg exposed to the combustion chamber. In other words, the greater the rate of increase in the cross-sectional area toward the stepped portion, the better the heat flow, and the less likely pre-ignition will occur. And the value is B/M≦0.854 for the mounting screw diameter. The effect is great when both C/M≧0.4- are satisfied. Self-cleaning performance is evaluated by the vehicle speed at which the carbon attached to the tip of the insulator is cleaned. To clean this carbon, the temperature of the insulator must rise to a certain temperature or higher. If the insulator is as thin as As2.0 and has a small heat capacity, the temperature will rise even more with less specific heat, and self-cleaning performance will also improve. In addition, providing a vc-"trade part has better self-cleaning properties, but since the efficiency of heat conduction is affected by the cross-sectional area of the insulator, it is desirable that the straight part be shorter, or at least 5ff or less.

Example The present invention will be explained below with reference to embodiments of the drawings.

Figure 1 shows an insulator made of AIN ceramic with a thermal conductivity of 60 W/mk or more, and 2 is a Pt central pole.

The Ir-mat is made of noble metal materials such as Pt-Ir and Ir-Ni'4, and is partially provided with a flange 2a. ++i
The shaft hole 'J) of the insulator J) is inserted into the small diameter hole la with the tip r protruding, and the part 2a is locked to the step part 1b, and then the insulator is fired and held together. , an intermediate 'ft1 of W, Mo, Mo5iz, etc. is placed in the shaft hole of the center electrode 2.
A is connected by welding, brazing, etc., and conductive benign glass 4 or a resistor is cut and heat-sealed together with the terminal electrode 5. Reference numeral 6 denotes a main metal fitting provided with an engine mounting screw 6a, into which the insulator 1 is inserted and fixed to the crotch seat 6b via a packing 7ft by a known method. 8 is an outer electrode joined to the end surface 6cK of the metal shell 6, and is a spark plug in which a spark gap 9 is formed between it and the tip surface of the center 'gL pole 2. Furthermore, the center?
[After connecting i2 and the intermediate electrode 3, it may be inserted into an insulator and fired simultaneously.

In the spark plug of the present invention, as shown in an enlarged sectional view of the main parts in FIG. 2, the insulator tip diameter A1, the insulator body diameter B1, the insulator step part C, and the main metal fitting mounting screw 6b.
When set to MM, As2.9ff.

It is formed to satisfy B/M≦0.35 and C/M≧0.4. The physical properties of the AIN insulator used in the invention are shown in the table below.

Next, we will discuss the reasons for limiting the numerical values of the present invention.The sample was a silk plug with a mounting screw diameter of M14, the leg length of the insulator (the length from the tip to the stepped part) was 20mm, and the stepped part <"4C'fc6.7Hφ
(The relationship between the dimensions of B and A and performance is shown by fixing C/M = 0.48 >.

Figure 4 shows the relationship between 8 dimensions and heat resistance. The test is 160
Evaluation was made using the pre-ignition advance angle under the conditions of 0CC 4 cylinders, 5500 r I)mX4/4.

As a result, the smaller the 3rd dimension, in other words, the larger the difference from the insulator step, the better the heat resistance, and the 8th dimension is 4.9Uφ or less (
B/M=0. ．． 85 or less) is preferred. Figure 5 shows the relationship between the diameter A of the insulator tip and self-cleaning performance. The sample shows a relationship between A dimension and self-cleaning property when B is 8.6 mlφ (B/M=0.26) in the above dimensions, and the test was conducted in advance with a superrich mixture. An insulator with carbon attached to the leg length was prepared, and the self-cleaning speed of each sample was determined using a completed car with 1,600,004 cylinders. As a result, the self-cleaning effect was observed when the large dimension was 2.Offφ or less. Further, it is preferably 1.5 mlφ or less.

FIG. 3 is a sectional view of main parts showing another embodiment of the present invention,
The difference from the above Fig. 2 is that a cylindrical straight part 1e is formed following the tapered part 1d at the tip of the insulator 1, and the length L of the straight part 1e is 5M or less. Self-cleaning properties can be improved. However, if the length is too long than 51, the heat conduction effect will be impaired and the heat resistance will be reduced, which is undesirable. Gold A≦2.0MB/M≦0.
35. It is formed to satisfy C/M≧0.4, and a straight part of 5 dg or less is provided following the tapered part of the tip, increasing the degree of freedom in the shape of the insulator leg length, improving heat resistance and self-cleaning. You can get a spark plug with excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part of a spark plug showing an embodiment of the present invention, FIG. 2 is an enlarged sectional view of the main part of FIG. 1, and FIG. 3 is a sectional view of a spark plug showing another embodiment of the invention. The enlarged sectional views of the main parts, FIGS. 4 and 5 show the performance characteristics, FIG. 40 is a graph showing the relationship between the 8 dimensions and heat resistance, and FIG. 5 is a graph showing the relationship between the A dimension and self-cleaning property. 1...AIN insulator 1d...Taper part ]e・
・Straight portion 2 ・Center electrode patent applicant NGK Spark Plug Co., Ltd.

Claims (2)

[Claims] (1) In a spark plug formed by integrally firing an aluminum nitride insulator with a thermal conductivity of at least 60 W/mk or more and a center electrode made of a noble metal, the insulator tip diameter is A, and the insulator body at the end face of the metal shell When the diameter is B, the step diameter of the insulator is C, and the mounting screw diameter of the metal shell is M, it is characterized by satisfying the following conditions: A≦2.0mm, B/M≦0.35, and C/M≧0.4. Spark plug. (2) A spark plug characterized in that the insulator according to claim 1 is provided with a straight portion having a length of at most 5 mm following the tapered portion at the tip.