JPH031471A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent an insulating member from damage such as cracking by putting conductive powder in the gap between a discharge part electrode made of a noble metal and an intermediate electrode arranged together with a glass seal, which is encapsulated in the shaft hole of the insulating member. CONSTITUTION:To join electrically a discharge part electrode 3 made of a noble metal with an intermediate electrode 8, the gap between them is filled with a conductive powder 4. The thermal stress due to different expansions between the insulating member 2 and intermediate electrode 8 varying with temp. difference, which is generated when an internal combustion engine is operated is absorbed by compression of this powder 4, which prevents the insulating member 2 from damage such as cracking. The particle dia. of the powder 4 shall preferably be 10-120mum, while the filling volume V0 be 0.5<=V0<=15mm<3>, as too small volume can not satisfactorily absorb the thermal stress and a too large volume may bring about a rise in the discharge voltage.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention provides a spark plug for use in an internal combustion engine.
In particular, it concerns intermediate electrodes.

(Prior Art) Conventionally, in spark plugs used in internal combustion engines, especially in the intermediate electrode, in order to ensure electrical continuity with the discharge part electrode that is joined without any gap to the tip of the insulator, , it is common practice to weld an integrally formed intermediate electrode to a discharging section electrode at the tip, and to weld the distal end of the intermediate electrode in close contact with the rear end of the discharging section electrode in diagonal directions relative to the axis. There has also been proposed a method in which this is ensured by cutting to achieve surface contact (such as JP-A-63-136-483).

(Problem to be solved by the invention) However, in the above-mentioned conventional method, in order to establish electrical continuity with the discharge part electrode, an integrally formed intermediate electrode is welded to the discharge part electrode at the tip. If there is a significant difference between the linear expansion coefficient of the metal that makes up the intermediate electrode and the ceramic that makes up the insulator, the large temperature difference that occurs when the internal combustion engine starts and stops will cause the intermediate electrode to Stress is generated between the electrode and the insulator, which may cause the insulator to crack. Therefore, in order to prevent the insulator from cracking due to this difference in linear expansion coefficient, the ceramic that makes up the insulator is Kovar, which has a coefficient of linear expansion that is almost the same as that of , has been used for the center electrode, but since Kovar itself is expensive, it has the disadvantage of significantly increasing costs. In addition, as in JP-A No. 63-136483, when electrical continuity between the discharge section electrode and the intermediate electrode is achieved by bringing surfaces cut obliquely to the axis into surface contact with each other, the intermediate electrode A gap is likely to occur between the engine and the discharge part electrode due to vibration or thermal contraction, and as this gap occurs, the discharge voltage, that is, the voltage required by the internal combustion engine, increases, resulting in misfires, etc. at high rotation speeds or long running times. This has the disadvantage of causing damage to the internal combustion engine. Therefore, the present invention aims to improve the above-mentioned drawbacks of the conventional ones, and uses a simple structure to ensure the electrical connection between the intermediate electrode and the discharge part electrode, and also to prevent damage to the insulator caused by thermal stress. The aim is to prevent

(Means for solving the problem) To achieve this, conduction is made between the noble metal discharge part electrode, which is joined to the tip of the insulator without a gap, and the intermediate electrode, which is arranged together with the glass seal part sealed inside the shaft hole of the insulator. Electrical connection is achieved by filling the conductive powder with a particle size of 10 to 120 μm, and the volume (V0) of the filled portion is 0.5≦v.

≦15 (mm).

(Function) With the above configuration, the thermal stress caused by the difference in thermal expansion between the intermediate electrode and the insulator due to the heat generated from the stoppage of the internal combustion engine to its operation can be alleviated by the movement of the powder. Moreover, by adjusting the degree of filling of the powder constituting the intermediate electrode, the electrical connection with the discharge part electrode made of noble metal can be easily maintained and reliably obtained.

(Embodiment) The present invention will be further explained with reference to the embodiment shown in the drawings. (1) is a spark plug for an internal combustion engine comprising an embodiment of the invention. An insulator (2) that connects and secures a discharge part electrode (3) made of a noble metal without any gaps by the contraction force caused by co-firing, and a terminal at the rear of a shaft hole (5) drilled inside this insulator (2). A glass seal (7) and a resistor 13) are enclosed together with the electrode (6), and at the front, an intermediate electrode (8) made of metal or the like is inserted and pressed to form a single body, and a conductive powder (4) is inserted. (9) is an embodiment of the present invention applied to an internal combustion engine. The threaded part (10) and outer electrode (
14).

Conductive powder (4) is used to establish electrical connection between the discharge part electrode (3) made of noble metal and the intermediate electrode (8).
), it is an insulator (2) that changes with the temperature difference that occurs when an internal combustion engine is operated.
The conductive powder (4) can be compressed to absorb the thermal stress caused by the difference in expansion between the conductive powder (4) and the intermediate electrode (8), thereby preventing damage such as cracking of the insulator (2).

Furthermore, if the particle size of the conductive powder (4) to be filled and the volume required for its filling are too large, the mobility of the conductive powder (4) due to compression etc. will be impaired. Since sufficient electrical connection cannot be ensured, the particle size should be 10 to 120 μm, preferably an average particle size of 40 to 60 μm.
μm, and if the filling volume of the conductive powder (4) is too small, it may cause thermal stress caused by the difference in thermal expansion coefficient between the insulator (2) and the intermediate electrode (8). The volume (Vo) should preferably be 0.5≦vo≦15 (mm), since it will not be able to absorb enough water, causing cracks in the insulator (2), and an increase in discharge voltage if it is excessive. Become something.

In the case of this intermediate electrode (8), the metal body may be a nickel alloy (8ON i-20Cr, Inconel, Kovar, etc.), a copper alloy (OFHC steel, tough vinyl steel, electrical steel, etc.), or a conductive ceramic. Solids (MoSi2, SiC
, carbon rod, ZrB2, etc.), insulating ceramic (
It is possible to use AIN, BN, A12o9, BeO, etc. whose surface is metallized or plated) or a solid resistor (SiC, etc.), and its shape is such that a flange (11) is provided at the top. Also, taper the tip part (
12) (Fig. 3), the contact area with the conductive powder (4) to be filled may be increased. Further, as the conductive powder (4) to be filled, metal powder (at least one of PT, Cu, Ni, or Kovar), conductive ceramic powder (Ti, Zr, Hf, Cr, etc.), (At least one type of borides or silicides of group transition metals) or metal-coated ceramic powder (at least one type of alumina, aluminum nitride, or nickel-coated MoSi2). Further, for the discharge part electrode (3), a cermet electrode can be used in addition to iridium, which is a noble metal, a PT gold alloy.

(Effects of the Invention) As described above, thermal stress caused by heat can be reliably absorbed by filling electrically conductive powder between the intermediate electrode and the discharge part electrode made of noble metal. This has the excellent effect of preventing damage such as cracking of the insulator and ensuring sufficient electrical connection.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view of a spark plug for an internal combustion engine, which is an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of its main parts.
FIG. 3 is a side view showing another shape of the intermediate electrode. 1...Spark plug for internal combustion engine 2...Insulator 3
... Discharge part electrode 4 ... Conductive powder 5 ... Shaft hole 6 ... Terminal electrode 7 ... Glass seal 8 ... Intermediate electrode 9 ... Metal shell 10 ... Threaded part 11 ...
Flange part 12... Taper part 13... Resistor Figure 1 Patent applicant Agent Patent attorney Yuki Fujiki Figure 2 Figure 3

Claims (2)

[Claims] (1) There is conductivity between the noble metal discharge part electrode, which is bonded and held without a gap to the tip of the insulator, and the intermediate electrode, which is placed together with the glass seal part sealed within the shaft hole of the insulator. A spark plug for internal combustion engines filled with powder. (2) The particle size of the conductive powder filled between the discharge part electrode and the intermediate electrode is 10 to 120 μm, and the volume (V_0) of the filled part is 0.5≦V_0≦15 (mm^3). A spark plug for an internal combustion engine according to claim (1).