JPH0229678Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Field of Application] The present invention relates to a spark plug for an internal combustion engine (hereinafter referred to as a spark plug) that uses a noble metal chip in the discharge part in order to improve ignitability, spark flying properties, and durability. [Prior art] Conventionally known spark plugs in which a precious metal is provided in the spark discharge part are disclosed in Japanese Utility Model Publication No. 53-38046 and Japanese Patent Application Laid-Open No. 1983-1989.
-Described in Publication No. 66945. FIG. 1 shows the former embodiment, and FIG. 2 shows the latter embodiment. [Problem to be solved by the invention] According to this spark plug, the precious metal chips provided in the center electrode and the ground electrode are made of platinum, but the chips tend to crack, peel off, and fall off during long-term use. There is the problem of inviting. Therefore, the present invention provides a spark plug for an internal combustion engine that can prevent the precious metal chip from cracking, peeling, or falling off even during long-term use, thereby improving its durability. [Means for Solving the Problems] First, the present inventors were able to improve the material strength of the precious metal chip itself by mixing other metals into platinum that forms the precious metal chip.
Cracking, peeling, and peeling of precious metal chips during long-term use
Thinking that it would be possible to prevent it from falling off, we worked hard to find the optimal metal to mix with platinum. As a result, the present inventors discovered that other precious metals are suitable as materials with good solid solubility with platinum, which forms conventional precious metal chips. We have found that iridium is the most suitable metal for this purpose, and we have found the optimum mixing ratio of iridium. Therefore, the present invention provides a spark plug for internal combustion engines equipped with a center electrode and a ground electrode, in which the tip of the ignition part of the center electrode is formed into a small diameter straight rod shape that is smaller in diameter than the body of the electrode. The small part and the body are connected by a truncated conical part,
The center electrode is made of a nickel-based alloy, and the tip end face of the small part of the center electrode is made of a noble metal in which in a binary system of iridium and platinum, iridium is more than 20% by weight and 30% by weight or less, and the balance is platinum. The chips are joined by welding, and a precious metal chip containing more than 20% by weight and less than 30% by weight of iridium in the binary composition of iridium and platinum, with the balance being platinum, is joined by welding to the surface of the ground electrode facing the precious metal chip. However, a technical measure is adopted in which an alloy layer is formed on the welded joint surfaces of both noble metal chips to the center electrode and the ground electrode. [Example] The present invention will be described in detail below with reference to examples shown in the drawings. FIG. 3 shows the overall structure of the spark plug according to the present invention, and FIG. 4 shows an enlarged view of the main parts. In both figures, 1 is a center electrode made of a heat-resistant, corrosion-resistant, and conductive base metal, such as a Ni-Cr alloy, and the diameter of the tip of the center electrode 1 on the ignition part side is equal to the diameter of the body held by the insulator 3. It is thinner than 1a and shaped like a straight rod. This small diameter portion 1b is located at the upper end of the body portion 1a. Note that 1c is a truncated conical portion having a predetermined angle, and communicates between the small diameter portion 1b and the body portion 1a. 2 is a disk-shaped precious metal chip,
For example, Pt85% to 70% by weight, Ir (iridium)
It consists of a composition of more than 20% by weight and less than 30% by weight, and has dimensions of 0.7mm in diameter and 0.3mm in wall thickness.
4 is a central shaft made of carbon mesh, which has a shaft hole 3a in the insulator.
It is inserted into the upper part. 5 is a terminal made of brass or the like, and is screwed and fixed to the head of the center shaft 4.
Reference numeral 6 denotes a cylindrical housing made of metal made of carbon mesh, and a ring-shaped airtight packing 7 and a caulking ring 8 are provided inside the housing 6.
The above-mentioned insulator 3 is fixed via. The housing 6 is provided with a threaded portion 6a for fixing it to the engine block. Reference numeral 9 denotes a ground electrode made of a corrosion-resistant, heat-resistant, and conductive metal, and is fixed to the lower end surface of the housing 6 by welding. A spark gap G is formed between the ground electrode 9 and the center electrode 1. 10 is a noble metal chip provided on the ground electrode 9 at a position opposite to the noble metal chip 2 on the center electrode 1;
resistance welded. For example, this composition is Pt85
~70%, Ir is greater than 20% and less than 30%, and the shape is 1.2 mm in diameter and 0.2-0.3 mm in wall thickness. Reference numeral 11 denotes a conductive glass sealing layer sealed inside the shaft hole 3a of the insulator 3, and is composed of shell powder and low melting point glass.
are electrically connected to each other, and both are fixed in the shaft hole 3a of the insulator 3. In the above configuration, the operation will be explained next. The embodiment of the present invention uses a very small amount of precious metals, aiming to achieve the same performance as conventional spark plugs that use a large amount of precious metals, and is equivalent in terms of ignitability, spark resistance, and durability. It is characterized by its performance. Among these, ignitability and flammability are determined by the shape, and these characteristics are maintained if the shape of the precious metal chip does not change during use. Therefore, the biggest problem is durability, or in other words, reliability, and it must be excellent in this respect. First, as a prerequisite for reliability, welding must be sufficient. Therefore, it is necessary that an alloy layer be formed over almost the entire surface of the noble metal chip to be joined.The resistance welding method is used in this invention, and since a considerable welding current flows, the top surface of the precious metal chip is centered, and the ground electrode is It will be located almost on the same plane as the end face of the base material. Next, in terms of reliability, the top and side surfaces of the precious metal chips must not crack, peel, or fall off during operation. Note that during operation, we believe that spark plugs using this precious metal chip are maintenance-free, which is equivalent to the lifespan of the vehicle, so it is desirable that they do not peel or fall off within at least 100,000 km. We experimentally discovered that the cracks that lead to peeling and falling off are influenced by the material, and we found that materials with large grain sizes, such as pure platinum, are particularly prone to cracking. In addition,
Here, cracks are mainly considered to be cracks from the top surface of a precious metal chip. However, cracks from the sides of precious metal chips are excluded here because they are mainly affected by the base material of the ground electrode. Furthermore, cracks from the side surfaces can be adequately dealt with by changing the design by increasing the cross-sectional diameter of the precious metal chip by several hundred microns. The experimental results are shown below. Refrigeration cycle test - held at 850℃ for 6 minutes,
It is then kept at room temperature for 6 minutes. Repeat this. Table 1 shows the degree of crack progression when - is repeated 200 times.

[Effect of idea]

According to the present invention described above, the following effects are achieved. (1) Since precious metal chips are welded to both the center electrode and the ground electrode, spark consumption of both electrodes due to spark discharge can be avoided, and a spark plug with an extremely long life can be provided. (2) The noble metal chips bonded to each electrode by welding have better durability than those in which the electrodes are coated with a noble metal layer, and will not peel off. (3) Since a precious metal chip is joined to each electrode by welding, there is no need for extremely complicated manufacturing processes such as plating and vapor deposition, which are required when coating precious metals. Spark plugs using precious metal chips are easy to manufacture. (4) The noble metal chip of each electrode is made up of platinum-iridium binary system in which iridium is more than 20% by weight and less than 30% by weight, and the remainder is platinum. It is possible to prevent the occurrence of linear cracks, and the peeling and falling off of precious metal chips can be suppressed. (5) Each noble metal chip connected to the center electrode and the ground electrode is welded to each electrode. Since an alloy layer is formed on the joint surface, the noble metal chip and each electrode are firmly bonded via the alloy layer. As a result, separation of the noble metal chips from each electrode joint surface due to repeated heating and cooling cycles can be suppressed. (6) The tip of the firing part of the center electrode is formed into a small diameter straight rod shape that is smaller in diameter than the body of the electrode, and a truncated conical part is formed between the small diameter part and the body. Because of the connected structure, the required voltage for sparking is low due to the presence of the small diameter portion of the straight rod, and the sparking property is excellent, and the ignition property is excellent, which facilitates the growth of fire kernels. In addition, since the truncated conical portion is provided, the small diameter portion of the straight rod has excellent resistance to breakage. (7) As mentioned above, the tip of the firing part of the center electrode is a straight rod with a small diameter and has a smaller cross-sectional area than the body, but since the electrode is made of a nickel-based alloy, The heat received by the rod is well transferred to the body, and even if the straight rod has a small diameter portion, heat will not be trapped in the small diameter portion and cause pre-ignition or welding. Therefore, various adverse effects due to poor heat conduction will not occur, as would be the case, for example, when the center electrode having the tip shape of the firing part is entirely made of platinum-iridium.

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional views showing conventional known examples,
FIG. 3 is a half sectional view showing an embodiment of the present invention, and FIG. 4 is an enlarged sectional view showing the main part of FIG. 3. DESCRIPTION OF SYMBOLS 1... Center electrode, 1a... Body part, 1b... Small diameter part, 2... Center side noble metal chip, 9... Ground electrode, 10... Ground side noble metal chip.

Claims (1)

[Claims for Utility Model Registration] In a spark plug for an internal combustion engine equipped with a center electrode and a ground electrode, the tip of the ignition part of the center electrode is formed into a small diameter straight rod shape that is smaller in diameter than the body of the electrode. At the same time, the small diameter portion and the body portion are connected by a truncated conical portion, the center electrode is made of a nickel alloy, and the tip end face of the small diameter portion of the center electrode is coated with iridium. In a two-component system of platinum, noble metal chips containing more than 20% by weight and less than 30% by weight of iridium, with the balance being platinum, are joined by welding, and the surface of the ground electrode facing the noble metal chip is coated with iridium-platinum. Precious metal chips having two components in which iridium is more than 20% by weight and less than 30% by weight and the remainder is platinum are joined by welding, and an alloy layer is formed on the welded joint surfaces of both precious metal chips to the center electrode and the ground electrode. A spark plug for an internal combustion engine, characterized in that: