JPH04242090A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide a spark plug which can make its discharge voltage low, make its life long, and also make its manufacturing cost and manhours required low. CONSTITUTION:A chip 4 made of noble metal which is formed with grooves 41 in advance, is welded and fixed to the end face of a center electrode 2 faced to a grounding electrode 3. In this case, H represents the depth of each groove 41, W represents the width of each groove, D represents the diameter of the end face, S represents the overall area of the end face including the grooves 41, and S1 represents the overall area of the end face excluding the grooves 41. And the relation should be set up as follows, W>=0.15mm, 1.0mm<=D<=2.5mm, 0.2<S1/S<1.0, and H<=(S1/S-0.2)XS<1/2>X0.9mm. The aforesaid chip made of noble metal can easily be welded to the end face of the center electrode, and as far as the chip is manufactured so as to meet the dimensions as described herein above, the grooves will never be crushed. The presence of the grooves keeps discharge voltage low, the life of the chip can be lengthened because it is made of noble metal, and it is easy and low in cost to manufacture the chip because it only depends on welding.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug for an internal combustion engine, and more particularly to a spark plug that has a low discharge voltage, has a long life, and is easy to manufacture.

0002

[Prior Art] Against the background of recent demands for exhaust gas purification, it has been desired to start the ignition of an internal combustion engine using a lean air-fuel mixture. A noble metal tip, mainly made of Pt, is bonded to the tip surface of the tip.

On the other hand, in Japanese Patent Publication No. 52-39143 to Japanese Patent Publication No. 59-33949, an attempt has been made to lower the discharge voltage by providing grooves or depressions on or near the tip of the center electrode.

0004

[Problems to be Solved by the Invention] Therefore, if a groove is formed in the noble metal tip, a spark plug with a long life and a low discharge voltage can be obtained, but if the noble metal tip bonded to the center electrode is formed with a groove. In order to form a ring, it is necessary to use one with a larger diameter than necessary in consideration of misalignment, etc., and there is a problem that precious metal material is wasted and manufacturing is time-consuming.

[0005] In order to solve this problem, it may be possible to weld a noble metal tip with a groove formed in advance to the end face of the center electrode, but the groove is often crushed due to resistance heat generation and pressure caused by the current during welding. There was a problem.

The present invention has been made to solve the above problems, and an object thereof is to provide a spark plug for an internal combustion engine that can suitably weld a noble metal tip to a center electrode, has a long life, has a low discharge voltage, and is easy to manufacture. do.

[0007]

[Means for Solving the Problems] To explain the structure of the present invention, a spark plug for an internal combustion engine includes a cylindrical insulator 1 provided in a housing 5 installed in the internal combustion engine, and a center electrode 2.
A ground electrode 3 is provided to face the center electrode 2, and a columnar noble metal tip 4 is welded to at least one of the opposing surfaces of the center electrode 2 and the ground electrode 3 at one end surface thereof. , a groove 41 is formed on the other end surface of the noble metal tip 4 before welding, and the depth of the groove 41 is set to H.
, the width of the groove is W, the diameter of the end face is D, the total area of the end face including the groove 41 is S, the area of the end face excluding the groove 41 is S1, and W
≧0.15mm 1.0mm≦D≦2.5mm 0.2<S1/S<1.0 H≦(S1/S−0.2)×√S×0.9mm.

[0008] According to the spark plug having such a structure, the noble metal tip 4 can be well bonded to the opposing surface of the center electrode 2 by applying the necessary welding current and pressure, and the groove 41 is not crushed, and the formed groove 41 is not crushed. The grooves 41 realize a sufficiently low discharge voltage.

[0009]

[Embodiment] In FIG. 2, a housing 5 made of a metal cylinder is attached to the cylinder head of an internal combustion engine by a threaded portion 51 on the outer periphery of the lower end, and the lower half of a cylindrical insulator 1 is inserted and fixed into the housing 5. , a center electrode 2 is fixed in the lower end. The center electrode 2 has an inner material made of copper and an outer material made of a Ni-based alloy. A center shaft 6 is inserted into the upper half of the insulator 1, and the upper end thereof exposed to the outside of the insulator 1 serves as a terminal 61. The lower end of the center shaft 6 is heat-welded to the upper end of the center electrode 2 with a conductive glass sealing material 7. Center electrode 2
The lower end face of the insulator is exposed to the outside of the insulator, and a noble metal tip 4, which will be described in detail later, is welded and fixed to this end face. On the other hand, an L-shaped ground electrode 3 extends from the lower opening edge of the housing 5, and its tip faces the noble metal tip 4 to form a discharge gap.

The details of the noble metal tip 4 are shown in FIG. 1. The tip 4 has a cylindrical shape, and one end surface is welded to the lower end surface of the center electrode 2, and the other end surface facing the ground electrode 3 has a cross shape. A groove 41 is formed. Here, the groove 41 has a depth H and a width W, and the area of the end surface including the groove 41 is S, and the groove 4
The area of the end face excluding 1 is S1, and the end face diameter is D. In addition, the material for the noble metal tip 4 is preferably one that has wear resistance, excellent high temperature strength, and high hardness, such as Pt-Ir, Pt
-Platinum alloy such as Ni, Pt-W, preferably 70-85
Alloy of WT% and 30-15WT% Ir, 30-15WT
P consisting of %Ir and 0.5-2.0WT%Ni remaining Pt
t-Ir-Ni alloy, 80-90 WT% Pt and 20-1
Alloy of 0 WT% Ni, 95-97 WT% Pt and 5-3 W
An alloy of T%W is used.

The noble metal tip 4 having such a structure is used as the center electrode 2.
When welding to the center electrode 2, as shown in Fig. 3(a),
The noble metal tip 4 is positioned on the end face of the welding machine, and a welding electrode rod 8 of a resistance welding machine is pressed from above and energized. Due to this current, Joule heat is generated at the joint surface between the noble metal tip 4 and the center electrode 2, and a part of the chip 4 is buried in the base material of the center electrode 2, making the joint part slightly larger in diameter. Welding is completed (FIG. 3(b)). At this time, unless certain conditions are satisfied, the groove depth H1 after welding will be smaller than the depth H before welding, that is, the groove 41 will collapse.

The results of experiments conducted under various conditions are shown in FIGS. 4 to 7 below. This experiment used a cross groove as shown in Figure 4, and the dimension from the bottom of the groove to the bottom of the chip was 0.3
It was kept constant at mm. In Figure 4, S1/S is changed by setting the tip diameter to 1.5 (that is, area S to 1.77).
For example, in S1/S━0.31, H━0.15, S1/S
It is known that for |0.84, H|0.7 is the limit.

[0013] In Fig. 5, S is changed as S1/S━0.5, and when S━0.79, H━0.2, S━4.9
1, it is known that H━0.6 is the limit for each. In FIG. 6, S is similarly changed as S1/S━0.7. In this case, S━0.79, H━0.4, S━4.
It is known that H━1.0 is the limit for 91.

FIG. 7 summarizes the above results.
The maximum value of the initial chip groove depth H with respect to the area ratio S1/S is shown by each straight line in the figure, with the area S of the end face of the noble metal tip 4 including the groove 41 (i.e., the chip diameter D) as a parameter, This is approximated by H━(S1/S-0.2)×√S×0.9 (mm). Therefore, the groove depth is appropriately selected to be less than or equal to the value obtained from this relational expression. In this case, D is 1.0 mm≦D because the diameter of the center electrode commonly used is 2.7 mm, and if the diameter is less than 1 mm, chip wear due to spark discharge will be large and the effect of lowering the discharge voltage will be small. ≦2.5
The range is mm. Also, from each straight line above, S1/S━
At 0.2, the groove depth H is zero, that is, collapse of the groove is unavoidable, so 0.2<S1/S<1.0 is set.

Furthermore, as shown in FIG. 8, a sufficient voltage reduction effect cannot be obtained unless the chip groove width W is 0.15 mm or more. In the figure, the line x is the experimental result for the cross-shaped groove, and the line y is the experimental result for the single-character groove.

Various groove shapes can be used for the noble metal tip 4, such as a V-section groove (FIG. 9(a)) and a U-section groove (FIG. 9(b)).
)), star-shaped groove (Fig. 9(c)), pattern-shaped groove (Fig. 9(d)
) etc. can be used.

If the noble metal tip 4 is also provided on the ground electrode 3 as shown in FIG. 10, there is an effect of further reducing the discharge voltage, or it may be provided only on the ground electrode 3.

[0018]

As described above, the spark plug of the present invention can sufficiently lower the discharge voltage, has a long life, and can greatly reduce the cost and labor of installing the noble metal tip.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the tip of a center electrode.

FIG. 2 is an overall sectional view of the spark plug.

FIG. 3 is a schematic cross-sectional view showing a process of welding a noble metal tip.

FIG. 4 is a graph showing experimental results.

FIG. 5 is a graph showing experimental results.

FIG. 6 is a graph showing experimental results.

FIG. 7 is a graph showing experimental results.

FIG. 8 is a graph showing experimental results.

FIG. 9 is a plan view and a cross-sectional view showing the shapes of various noble metal chips.

FIG. 10 is a side view of a center electrode tip showing another example of the present invention.

[Explanation of symbols]

1 Insulator 2 Center electrode 3 Ground electrode 4 Precious metal chips 41 Groove 5 Housing

Claims (1)

[Claims] Claim 1: A cylindrical insulator is provided in a housing to be attached to an internal combustion engine, a center electrode is inserted therethrough, a ground electrode is provided opposite the center electrode, and the opposing surfaces of the center electrode and the ground electrode are provided. A columnar noble metal tip is joined to at least one of the two end surfaces by welding, and a groove is formed in the other end surface of the noble metal tip before welding, and the depth of the groove is H, the width of the groove is W, The diameter of the end face is D, the total area of the end face including the groove is S, and the area of the end face excluding the groove is S1,
W≧0.15mm 1.0mm≦D≦2.5mm 0.2<S1/S<1.0 H≦(S1/S-0.2)×√S×0.9mm A spark plug for an internal combustion engine.