JPH0777157B2 - Spark plug - Google Patents

Description

The present invention relates to a spark plug having a center electrode of an internal combustion engine spark plug or a tip made of platinum or a platinum alloy at both ends of the center electrode and the outer electrode. The present invention relates to a spark plug with improved discharge characteristics.

(Prior Art) In recent years, spark plugs used in internal combustion engines are provided with a noble metal tip of platinum, platinum alloy, gold-palladium alloy or the like on the tips of the center electrode and outer electrode from the viewpoint of improving ignitability and maintenance-free. Spark plugs are known. As shown in Fig. 7, a typical one has a diameter of 2.5 mmφ.
The diameter d ₁ is 0.8 mmφ x length 0. at the tip (1a) of the frusto-cone (tip diameter d ₂ is 1.5 mmφ x length 0.8 mm) of the center electrode (1) of.
Ignition in which a cylindrical tip (2) of 7 mm platinum-iridium (20% Ir) alloy is welded, and the length L from the tip end surface of the center electrode (1) to the truncated cone portion is formed to 1.5 mm The shape of the center electrode of such a spark plug has the above-described dimensional relationship in consideration of thermal problems, manufacturing and ignitability.

(Problems to be Solved by the Invention) By the way, the conventional spark plug A having the center electrode of platinum or a platinum alloy on the center electrode side has a higher discharge voltage than that of a general nickel alloy electrode spark plug. As shown by the solid line, the maximum value was as high as 50%, and it was found that the variation was particularly large.

The possible reasons are as follows. That is, unlike nickel, platinum does not oxidize the discharge surface and is only partially melted by sparks, and the discharge surface of platinum becomes a mirror surface as the spark discharge progresses. For this reason, the electric field strength of the mirror-like portion is drastically reduced as compared with the rough surface having the unevenness due to nickel oxidation, and the discharge voltage is increased, and the chip surface is melted to be uniform and the discharge voltage is It is considered that the variation becomes large because it takes time due to the characteristics of the material until it becomes highly stable.

Therefore, in the present invention, the electric field reduction due to the roughness of the platinum chip surface becomes a problem. Therefore, by making the electrode shape and size of the center electrode that compensates for the reduction, the discharge voltage is reduced and the variation is reduced. An object is to provide a spark plug having a platinum tip.

(Means for Solving the Problem) A feature of the present invention is an ignition plug in which tips made of thin platinum or a platinum alloy are provided at both tips of a center electrode or outer electrodes of the center electrode, and a tip diameter d ₁ of the tip is provided. 0.5 to
The center electrode d ₂ is 1.0 mm, and the center electrode d _{2 at} a position at least 1.5 mm away from the tip end surface of the center electrode is 1.0 to 1.5 times the tip end diameter d _{1. 2} is formed to have a diameter smaller than the diameter d _{3 of the} center electrode base portion projecting from the tip of the insulator, whereby the discharge voltage of an ignition plug having a platinum-based tip on at least the discharge surface of the center electrode is shown in FIG. It has a stable spark discharge characteristic even when used for a long time, and prevents ignition of the ignition plug and stable ignition especially in a city running condition of 40 to 60 km / H. Can have sex.

(Example) The present invention will be specifically described below with reference to the drawings. 1 and 2 are spark plugs showing an embodiment of the present invention. FIG. 1 is a front view showing a cross section of a main part thereof, and FIG. 2 is a firing part of a center electrode of FIG. FIG.
(1) is a center electrode made of a nickel alloy or the like, and a good heat conductive material such as copper is enclosed in the center electrode. (2) is
Pt-Ir, Pt-Rh, Pt-Ru, Pt-Ir-Ni and other Pt alloys mainly composed of Pt, which are thin plates (0.5 to 1.0 mmφ) or columnar chips with a small diameter. The tip is welded to the tip (1a) of the center electrode (1) by electric welding or the like. (3) is an insulator, and the center electrode (1) is arranged so as to be exposed from the front end (3a) of the shaft hole and fixed by a known method such as glass sealing. (4) is a metal shell having a mounting screw (4a) on the tip side, and the insulator (3) is fitted and fixed in the inner cavity of the metal shell (4) and bent and joined to the lower end surface of the metal shell (4). A spark plug having a spark gap (6) formed between the side surface of the outer electrode (5) and the tip surface (2a) of the tip (2) of the center electrode (1), and the outer electrode (5). A tip (7) made of platinum or a platinum alloy may be provided on the side surface of the above, and a spark gap (6) may be formed between the tip (2) and the tip (2) of the center electrode (1). . In the present invention, the base portion of the center electrode (1) having the tip portion (1b) of the center electrode (1) joined to the tip (2) protruding from the tip (3a) of the insulator (3) as shown in FIG. The center electrode diameter d ₂ of the length l at least 1.5 mm away from the tip surface (2a) of the tip (2) with respect to the diameter d ₃ is the tip tip diameter d.
It is formed in a small diameter so as to be in the range of 1.0 to 1.5 times that of ₁ , and as a specific dimension, d ₂ is set to 0.5 to 1.5 mm. FIG. 3 and FIG. 4 show another embodiment of the present invention, in which the 1-dimensional portion from the tip end surface (2a) of the center electrode (1) is arranged in the range of the center electrode d _2. The taper shape is 1b-1 (Fig. 3) and the step shape is 1b-2 (Fig. 4). The processing of the l-dimensional portion can be performed not only by cutting but also by extrusion.

Next, the function and effect of the present invention will be described in comparison with a conventional spark plug. As shown in FIG. 7, a conventional platinum tip plug A has a center electrode (1) having a base diameter d ₃ of 2.5 mmφ.
Truncated cone (tip diameter d ₂ 1.5 mmφ x length 0.8 mm) tip (1
pt-Ir (20% I) where diameter d ₁ is 0.8mmφ x length 0.7mm in a)
r) An alloy tip (2) is resistance-welded. This conventional spark plug A has a frusto-conical length L from the tip of the tip of 1.5 mm and a center electrode base diameter d ₃ of 2.5 mmφ. It has an electrode shape. Therefore, the length l of the center electrode d ₂ of the conventional spark plug A corresponds to the length l _{1 of the} tip, and
Only 7mm is provided. On the other hand, as shown in FIG. 2, the spark plug B according to the present invention is formed by cutting l into a diameter of d ₂ of 1.2 mmφ over 1.5 mm, and the tip surface (2a) of the tip (2) is 0.2. The discharge voltage characteristics of the used product that was consumed were examined.

As a result, as shown in FIG. 5, the relationship between the pressure applied on the horizontal axis and the discharge voltage applied on the vertical axis is that the conventional spark plug A shows a variation in the range from MAX to MIN, as indicated by the solid line. 4kg / cm ² shows a remarkably high value at a so-called vehicle speed of 40 to 60km / H, whereas the spark plug B of the present invention has a large decrease in the discharge voltage MAX value as shown by the dotted line and there is little variation. Become. Fig. 6 shows the relationship between the discharge voltage and the l dimension from the tip surface (2a) of the center electrode (1) at a pressure of 4 kg / cm ^{2, which} is remarkable when the l dimension is 1.5 mm or more. can cause voltage drop, and the discharge voltage becomes low as the diameter of d ₂ of the portion it is thin, the d ₂
The effective diameter is 1.5 mmφ or less. Even if the conventional spark plug shown in FIG. 7 and 1 were 1.0 mm and the tip diameter or the diameter of d ₂ was reduced to 0.7 and 0.5φ, the discharge voltage could not be lowered and there was no effect.

(Effects of the invention) As described above, the spark plug including the platinum-based tip in the shape of the center electrode of the present invention has a low discharge voltage even when the spark discharge progresses, and particularly when the vehicle speed is 40 to 60 km / H. Since the reduction effect is remarkable and the variation is reduced in the inward traveling, there is an effect that the ignition mistake can be prevented and the stable drivability can be achieved.

[Brief description of drawings]

FIGS. 1 and 2 show an embodiment of the spark plug of the present invention. FIG. 1 is a front view showing a cross section of the main part thereof, and FIG. 2 is a view of the center electrode ignition part of FIG. Main part enlarged front view, No. 3
FIGS. 4 and 5 are enlarged front views of the main part of the center electrode ignition part showing another embodiment of the present invention, FIG. 5 is a graph showing the discharge voltage of the present invention spark plug and the conventional spark plug, and FIG. Graph showing the relationship between the discharge voltage and the l dimension and d ₂ dimension, No. 7
FIG. 1 is an enlarged front view of a main part of a center electrode ignition part of a conventional spark plug. 1 ... Center electrode, 1b ... Tip part, 2 ... Chip, 2a ...
The tip end face, 5 ...... outer electrode, 7 ...... chip, d ₁ ......
Tip tip diameter, d ₂ …… l dimension diameter

Claims (1)

[Claims] 1. A spark plug having a tip made of thin platinum or a platinum alloy at both tips of a center electrode or an outer electrode of the center electrode, wherein a tip diameter d ₁ of the tip is 0.5 to 1.0.
mm, the center electrode d _{2 at} a position at least 1.5 mm away from the tip end surface of the center electrode is 1.0 to 1.5 times the tip end diameter d ₁ , and the center electrode d ₂ Is the diameter of the base of the center electrode protruding from the tip of the insulator d ₃
A spark plug characterized by being formed to have a small diameter.