JPH04264378A - Earth electrode for spark plug - Google Patents

Abstract

PURPOSE:To obtain earth electrode having excellent heat emitting property, high temperature oxidation corrosion resistance and spark durability by forming an earth electrode with multiple layers of clad material, and specifying the number of each layer and thickness thereof. CONSTITUTION:The most outer layer 10 of an earth electrode 9 is made of corrosion resistance nickel alloy having a room temperature heat conductivity less than 20W/mK, and a central part 11 is made of pure nickel having a room temperature heat conductivity more than 80W/mK. Multiple layers of pure nickel layer 12 and corrosion resistance nickel alloy layer 13 having a room temperature heat conductivity less than 20W/mK are located between the most outer layer 10 and the central part 11. When t1 means thickness of the most outer layer 10, t2 means thickness of the multi-layer part 14, and T means sum of thickness of the most outer layer 10 and the multi-layer part 14, 0.02<=t1<=0.1mm, 0.1<=t2<=0.3mm, 0.3<=T. Furthermore, N means the number of layer of the multi-layer part 14 and K means ratio of thickness of the pure nickel layer 12 and the nickel alloy layer 13, 5<=N<=10.1<=K<=3, and thickness of each layer is more than 0.01mm.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a ground electrode for a spark plug used in an internal combustion engine.

0002

[Prior Art] Conventionally, the ground electrode of spark plugs used in internal combustion engines has generally been made of a single layer of nickel alloy, but in recent years, with the development of internal combustion engines, spark plugs used in internal combustion engines have In spark plugs, the ground electrode, which is exposed to high-temperature combustion gas, is particularly prone to thermal damage. Therefore, in the ground electrode of a spark plug, the inner core material is pure nickel or a nickel alloy with an additive metal content of 10 wt% or less, and the outer periphery is coated with chromium. A multilayer structure coated with a peripheral material made of a nickel alloy containing 10 wt% or more has been proposed (Japanese Patent Laid-Open No. 41785/1985).

0003

[Problems to be Solved by the Invention] However, in the case of JP-A No. 60-41785, in the conventional spark plug, the amount of pure nickel or additive metal added to the internal core material in the ground electrode of the spark plug is It has a multi-layer structure using a nickel alloy containing 10 wt% or less of chromium, and the outer periphery of the nickel alloy is coated with a nickel alloy containing 10 wt% or more of chromium, but the manufacturing process involves electrical resistance welding between the metal shell and the ground electrode. Since the core material and the outer material are made of materials with different electrical resistances, the electricity during welding tends to concentrate on the pure nickel of the core material, which has a low resistance, and therefore the outer material of the high chromium nickel alloy This results in insufficient welding of the materials, and cracks occur in the outer material during gap forming.

[0004]Although the high chromium alloy constituting the outer material has excellent oxidation resistance, the spark consumption during discharge is large, and the secondary current generated due to leakage current due to fouling of the spark plug, etc. Internal combustion engines employing a capacitor discharge type ignition system, which is advantageous in comparison with conventional engines, have the disadvantage that its characteristics cannot be fully utilized.

[0005] Therefore, the present invention aims to improve the drawbacks of the above-mentioned conventional products, and is designed to meet the needs of internal combustion engines, which have become more sophisticated in recent years, by providing excellent heat dissipation properties, as well as high-temperature oxidation corrosion and spark consumption properties. The purpose is to provide a ground electrode for spark plugs.

[0006]

[Means for solving the problem] To achieve this, the outermost layer is made of a corrosion-resistant nickel alloy with a thermal conductivity of 20 W/mk or less at room temperature, and the center layer is made of pure nickel with a thermal conductivity of 80 W/mk or more at room temperature. At the same time, a pure nickel layer and a corrosion-resistant nickel alloy layer with a thermal conductivity of 20 W/mk or less at room temperature are arranged in a multilayered manner between the outermost layer and the center, and the outermost layer has a thickness of t1, When the thickness of the multilayer part is t2, and the sum of the thicknesses of the outermost layer and the multilayer part is T, 0.02≦t1
≦0.1mm, 0.1≦t2≦0.3mm, and 0.3
≦T, and the area ratio of pure nickel in the cross section of the ground electrode is 50% or more.

[0007] In a multilayer part in which a pure nickel layer and a corrosion-resistant nickel alloy layer with a thermal conductivity of 20 W/mK or less at room temperature are arranged between the outermost layer and the center part, the number of layers is N, and a pure nickel layer is arranged between the outermost layer and the center part. The thickness ratio of nickel and corrosion-resistant nickel alloy is K (thickness of pure nickel/thickness of corrosion-resistant nickel alloy = K)
), 5≦N≦10, 1≦K≦3, and the thickness of each layer is 0.01 mm or more.

[0008]

[Function] With the above structure, the heat dissipation of the ground electrode of the spark plug, which is constantly exposed to high-temperature combustion gas in the combustion chamber of an internal combustion engine, can be improved by making it multi-layered. Since the outermost layer constituting the structure is made of a corrosion-resistant nickel alloy, it increases the resistance to spark wear during discharge, and there is a pure nickel layer between the outermost layer and the center and a thermal conductivity of 20 W/mK or less at room temperature. By arranging the corrosion-resistant nickel alloy layer in a multilayered manner, electric welding can be made good, and the bonding strength of the ground electrode can be stabilized and excellent in mass production.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be further explained with reference to embodiments shown in the drawings. (1) is a spark plug for an internal combustion engine which is an embodiment of the present invention;
) holds the center electrode (4) at the tip of the shaft hole (3), and also holds one end of the resistor (5) and the terminal electrode (6) sandwiched between the conductive glass seals (7) in the shaft hole (3). 3)
An insulator (2) sealed inside the insulator (2), and a ground electrode (9) at a position opposite to the tip of a center electrode (4) held at the tip of the shaft hole (3) of this insulator (2). It is composed of a metal shell (7) having a threaded portion (8) on its side periphery that is screwed into the internal combustion engine.

A ground electrode (9) is placed opposite the center electrode (4) held at the tip of the shaft hole (3) of the insulator (2) and is welded and joined to the metal shell (7). ), the outermost layer (10) is made of a corrosion-resistant nickel alloy with a thermal conductivity of 20 W/mk or less at room temperature, and the center part (11) is made of pure nickel with a thermal conductivity of 80 W/mk or more at room temperature, A pure nickel layer (12) between the outermost layer (10) and the center part (11) and a thermal conductivity of 20W/mk at room temperature
The following corrosion-resistant nickel alloy layer (13) is arranged in a multilayered manner, and the thickness of the outermost layer (10) is t.
1. The thickness of the multilayer part (14) consisting of the pure nickel layer (12) and the corrosion-resistant nickel alloy layer (13) is t2, and the sum of the thicknesses of the outermost layer (10) and the multilayer part (14) is T. 0.02≦t1≦0.1mm, 0.1≦t2≦0
．． 3mm, and 0.3≦T, and the ground electrode (9
) The area of pure nickel in the cross section is 50% or more.

[0011] At this time, the thermal conductivity at room temperature is 20 W/m
Thickness t1 of the outermost layer made of a corrosion-resistant nickel alloy of k or less
To make 0.02≦t1≦0.1mm, 0.02
If it is less than 0.1 mm, it will be easily worn out due to spark consumption during spark discharge, and if it is thicker than 0.1 mm, the ground electrode ( 9) consists of an outermost layer (10) and a center part (11) that have different electrical resistance values, so when electricity is applied, it tends to concentrate in the center part (11) with a low resistance value, and the thermal conductivity at room temperature decreases. Welding of the outermost layer (10) made of a corrosion-resistant nickel alloy of 20 W/mK or less becomes insufficient, and cracks occur when forming the gap between the ground electrode (9) and the center electrode (4), resulting in strength problems. Therefore, the thickness t1 of the outermost layer (10) is 0.02≦t1≦0.
1 mm, preferably 0.02 to 0.0
75 mm is good.

[0012] Also, the thickness t2 of the multilayer part (14) consisting of the pure nickel layer (12) and the corrosion-resistant nickel alloy layer (13)
The reason why the outermost layer (10) made of a corrosion-resistant nickel alloy is set to 0.1≦t2≦0.3 mm is that the outermost layer (10) made of a corrosion-resistant nickel alloy is worn out due to oxidative corrosion and spark discharge caused by high-temperature combustion gas during long-term use. (14) may be exposed, so it is considered advantageous to increase the thickness of the multilayer part (14), but considering the thermal conductivity of heat accompanying combustion, ~0.3mm is the limit, preferably 0.
．． 2 to 0.25 mm is appropriate.

[0013] If T is the sum of the thicknesses of the multilayer part (14) consisting of the outermost layer (10) made of a corrosion-resistant nickel alloy, the pure nickel layer (12), and the corrosion-resistant nickel alloy layer (13), then 0 The reason for setting 3≦T is that this part is involved in spark consumption associated with spark discharge, so the thickness must be at least 0.3.
It needs to be at least 0.3 mm, and in consideration of spark durability, it is preferably around 0.35 mm.

On the other hand, the area of pure nickel in the cross section of the ground electrode (9) is set to 50% or more because pure nickel itself has a very high thermal conductivity of 80 W/mk. If the area is large in the cross section of
The heat received by the ground electrode cannot be efficiently conducted, causing pre-ignition, but since the area of pure nickel in the cross section of the ground electrode (9) is more than 50%, This provides heat dissipation properties equivalent to those of a 95% nickel alloy electrode.

Furthermore, a pure nickel layer (12) is provided between the outermost layer (10) made of a corrosion-resistant nickel alloy and the center part (11) made of pure nickel, and the layer has a thermal conductivity of 20 W at room temperature.
In the multilayer part (14) in which corrosion-resistant nickel alloy layers (13) with a thickness of /mk or less are arranged in a multilayered manner, the pure nickel layer (12
) and the corrosion-resistant nickel alloy layer (13), that is, the number of layers is N, and the ratio of the thickness of pure nickel to the corrosion-resistant nickel alloy is K.
(Thickness of pure nickel/thickness of corrosion-resistant nickel alloy = K)
When 5≦N≦10 and 1≦K≦3,
In addition, each layer has a thickness of 0.01 mm or more.

At this time, the number N of layers of the multilayer part (14) in which the pure nickel layer (12) and the corrosion-resistant nickel alloy layer (13) having a thermal conductivity of 20 W/mk or less at room temperature are arranged in a multilayered manner is set to 5. ≦N≦10 is set because the number of layers N in the multilayer part (14)
If the number N is too large, the pure nickel layer (12) will be selectively oxidized due to the difference in oxidation resistance between the pure nickel layer (12) and the corrosion-resistant nickel alloy (13). On the other hand, if the number of layers N is too small, the metal shell This is because the electric weldability between the pure nickel layer (12) and the corrosion-resistant nickel alloy layer (13) deteriorates. When the ratio of the thickness of each layer is K (thickness of pure nickel layer/thickness of corrosion-resistant nickel alloy layer = K), 1≦K≦3 is satisfied, but the corrosion-resistant nickel alloy layer If the volume of (13) is too large, it is undesirable from the viewpoint of spark consumption, and if it is too small, it is unfavorable from the viewpoint of oxidation resistance.
．． A value of about 0 to 2.5 is good.

[0017] Furthermore, the thickness of the pure nickel layer (12) and the corrosion-resistant nickel alloy layer (13) is at least 0.01 mm because if it is thinner than this, breakage is likely to occur during the manufacturing process, and if it is too thick, This is because selective oxidation may be promoted.

Since the present invention has the above configuration, the ground electrode (9) has a center portion (11) of pure nickel and an outermost layer (11) of pure nickel.
0) is made of a corrosion-resistant nickel alloy, and a pure nickel layer (12) and a corrosion-resistant nickel alloy layer (13) are arranged between the center part (11) and the outermost layer (10), and these By applying regulations to each layer and making it multi-layered, the spark plug (1) is exposed to high-temperature combustion gas at all times in the direction of the metal shell (7) of the ground electrode (9) in the combustion chamber of the internal combustion engine. Since the outermost layer (10) constituting the multilayer structure is made of a corrosion-resistant nickel alloy, the spark wear resistance during discharge is improved, and the outermost layer (10) and the center Department (
11) and a pure nickel layer (12) and a corrosion-resistant nickel alloy layer (13) with a thermal conductivity of 20 W/mK or less at room temperature.
) in a multi-layered manner means that materials with different electrical resistances are arranged uniformly when electrical resistance welding is performed, so that the connection with the metal shell (7) by electrical resistance welding is good. Therefore, the bonding strength of the ground electrode (9) can be stabilized and excellent in mass productivity.

[0019] The ground electrode placed opposite the tip of the center electrode (4) held by the insulator (2) is
A pure nickel layer (12) and a corrosion-resistant nickel alloy layer (13) are placed around the pure nickel core material that is the central part (11).
A multi-layered sheet metal is wound, and both ends are welded by electron beam welding while vacuuming.
The buret is heated to approximately 1000°C in a heating furnace, and then subjected to a wire drawing process using hot isostatic extrusion.The resulting clad wire is then thinned by a cold wire drawing process. A pure nickel layer (12) is formed around the center part (11) made of pure nickel material by die-drawing or multifaceted rollers.
and a corrosion-resistant nickel alloy layer (13) arranged in a multilayered manner,
This is made by manufacturing a ground electrode material having a corrosion-resistant nickel alloy in the outermost layer (10).

Therefore, in order to confirm the extent to which the spark plug (1) for an internal combustion engine, which is an embodiment of the present invention, has improved spark consumption, it was installed in a 2000 cc, 6-cylinder engine, and the spark plug (1) for an internal combustion engine was used to generate approximately 50 mJ. When we conducted a continuous high-speed durability test for 200 hours using an ignition power source of induced spark energy, we found that the ground electrode made of pure nickel or 95% nickel alloy showed that the tip of the ground electrode started to oxidize during the test. Inconel 600 solid wood does not show any oxidation corrosion on the outside, but spark consumption is noticeable, and the outermost layer is made of Inconel 600 and the center is made of pure nickel. In this case, the wear of the outermost layer of Inconel 600 becomes noticeable, but in the example of this invention, a remarkable effect was observed (FIG. 4).

[0021]

[Effects of the Invention] As described above, by limiting the ground electrode to a certain value and making it made of a multilayer cladding material, the resistance to spark wear during discharge is improved, and the bonding with the metal shell is improved. It has the excellent effect of increasing strength and also ensuring mass productivity.

[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.

FIG. 2 is an enlarged sectional view of a main part of the ground electrode.

FIG. 3 is an enlarged sectional view of main parts in another embodiment.

FIG. 4 shows the results of a high-speed durability test. .

[Explanation of symbols]

1 Spark plug for internal combustion engine 2 Insulator 3 Shaft hole 4 Center electrode 5 Resistor 6 Terminal electrode 7 Main metal fittings 8 Threaded part 9 Ground electrode 10 Outermost layer 11 Center 12 Pure nickel layer 13 Corrosion resistant nickel alloy layer 14 Multilayer section

Claims (2)

[Claims] [Claim 1] The outermost layer has a thermal conductivity of 20 W/
A corrosion-resistant nickel alloy with a thermal conductivity of 80 W/mk or less is used in the center, and a pure nickel layer with a thermal conductivity at room temperature of 80 W/mk or more is formed between the outermost layer and the center. When corrosion-resistant nickel alloy layers of 20 W/mk or less are arranged in a multilayered manner, and the thickness of the outermost layer is t1, the thickness of the multilayer part is t2, and the sum of the thicknesses of the outermost layer and the multilayer part is T. , 0.02≦t1≦0.1mm, 0.1≦t
A ground electrode for a spark plug, which satisfies 2≦0.3 mm and 0.3≦T, and has an area ratio of pure nickel in the ground electrode of 50% or more. 2. In a multilayer part in which a pure nickel layer and a corrosion-resistant nickel alloy layer with a thermal conductivity of 20 W/mk or less at room temperature are arranged between the outermost layer and the center part, the number of layers is N, the pure nickel layer is The ratio of the thickness of nickel to corrosion-resistant nickel alloy is K(
A claim in which 5≦N≦10, 1≦K≦3, and the thickness of each layer is 0.01 mm or more, where thickness of pure nickel/thickness of corrosion-resistant nickel alloy=K) 1. The ground electrode of the spark plug described in 1.