JPS6333271B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a spark plug.

[Prior Art] Spark plugs are exposed to explosive gas that reaches temperatures of 2000°C or higher during high-speed operation, so it is necessary to dissipate this heat. Also, during low-speed operation, carbon and oil adhere and accumulate around the electrodes.
This needs to be burned out and cleaned. In order to prevent the spark plug from overheating and from adhering to carbon, etc. (smoldering), the temperature of the ignition part of the insulator of the ignition plug must always be within the temperature range of approximately 450 to 900℃. The temperature of the engine changes depending on the type of engine, operating conditions, type of fuel, and seasonal fluctuations in temperature and temperature. Therefore, in order for a spark plug to function satisfactorily under these conditions, it is necessary to efficiently release or retain the heat received from the engine as necessary to prevent the ignition part from overheating. be.

In conventional spark plugs, the center shaft plays an important role in drawing heat from the ignition part, and the center shaft is generally made of a single Ni alloy. but,
The thermal conductivity of this Ni alloy core remains almost constant depending on the temperature, or conversely tends to decrease as the temperature increases.

In addition, in order to increase thermal conductivity, other ignition plugs are manufactured using Cu, which has a Cu core placed in the center of the Ni alloy center shaft.
There are also spark plugs that use a cored Ni alloy center shaft. However, even with this spark plug, the thermal conductivity of the center shaft, and therefore the amount of heat transfer, remains almost constant even when the temperature changes.

Therefore, conventional spark plugs cannot reliably prevent overheating and smoldering.

[Problems to be Solved] An object of the present invention is to provide a spark plug that improves adaptability to temperature changes in the ignition part (achieves a wide range) and can prevent overheating and smoldering as much as possible. This issue is extremely important in the current situation where user demands are becoming increasingly strict.

[Means for Solving the Problems] The spark plug of the present invention includes a center electrode at the tip of a hollow insulator, and a metal spherical powder in the hollow part of the insulator and between the center electrode and the terminal shaft. The metal spherical powder is elastically deformable in the operating temperature range of the ignition part, and the rear end of the aggregate is sealed with a conductive sealing material. Features.

[Function] In the spark plug of the present invention having these characteristics, a predetermined powder aggregation exists in the hollow part of the insulator between the center electrode and the terminal shaft (the part where the center shaft conventionally existed). The body elastically deforms in response to the temperature near the tip of the insulator, that is, the ignition part, and the contact area between the powders changes, thereby effectively changing the amount of heat transfer.

Specifically, at low temperatures, the powder aggregate hardly deforms elastically, the contact area between the powders is small, and the amount of heat transferred by the aggregate is small, so that heat is retained in the ignition part. As a result, it contributes to cleaning by burning off carbon, etc. Conversely, at high temperatures, the amount of elastic deformation, contact area, and amount of heat transfer related to the powder aggregate are large, thus preventing overheating of the firing section and suppressing the occurrence of preignition.

This phenomenon will be explained using a diagram as follows. At low temperatures, each powder is in a normal tightly packed state (Fig. 3a), but as the temperature rises, individual powders undergo volumetric expansion within the range of elastic deformation, and the contact area between adjacent powders increases (Figure 3a). 3b), resulting in an increase in the amount of heat transfer. The graph in FIG. 4 is a qualitative diagram of this relationship. Note that the elastic deformation rate of simple metal spherical powder is greater than that of ceramic powder.

In addition, since ceramic powder is an essential element for powder aggregates, (compared to aggregates made only of metal spherical powders), it prevents the powders from becoming integrated due to fusion, etc., and prevents expansion and expansion due to elastic deformation. Contraction can be reliably repeated.

[Preferred embodiment] First, the metal spherical powder will be described.

Here, the term "spherical" refers to a general shape, and although it is preferable that the shape be completely spherical, it is not essential, and deformations defined by manufacturing conditions or the presence of deformed objects are allowed.

As a metal spherical powder, it has high thermal conductivity,
It is necessary to have an appropriate coefficient of expansion within a set temperature range, to remain in an elastic region, to have stability as the temperature decreases, and to have high repeatability. Metal spherical powder that satisfies this condition is
Examples include Cu, Fe, Ni, Cr and/or mixtures or alloys thereof, or alloys containing additive elements such as Sn, Zn, Al, and Pb. These metals are approximately
Within the elastic range of 450 to 900°C, it can repeatedly expand and contract (restoring) as the temperature rises and falls. At this time, the amount of heat transfer increases or decreases almost in proportion to the heat transfer area, and it becomes possible to control the amount of heat transfer according to the increase or decrease in the contact area between the spheres.

The particle size of metal spherical powder is approximately 1000μ or less,
Preferably, those having a diameter of 800μ to 200μ are used. Cu
As an alloy, for example, in weight percent, Cu70~95%, balance Ni (cupronickel), Cu97~99.5%, balance Cr (chromium copper),
Cu alloy etc. can be used, and other materials such as
Zn5~20% balance Cu (brass), Sn4~8%, P0.1%,
The balance is Cu (phosphor bronze), Al8~10%, Ni1~5%,
Copper alloys such as 2.5 to 3.0% Fe and the balance Cu (aluminum bronze) could be used advantageously.

In the present invention, ceramic powder is an essential element along with the metal spherical powder.

Examples of this ceramic powder include Al ₂ O ₃ ,
Materials with relatively good heat conductivity such as SiC, AlN, TiN, TiC, ZrC, and B ₄ C are used, and the particle size is approximately 500μ.
Hereinafter, a material of approximately 200 μm or less is preferably used.
The content of this ceramic powder is about 40% by volume or less, preferably about 10 to 30% by volume, based on the total amount of the powder aggregate, and its content prevents sintering of the metal spherical powder and also prevents the powder from aggregating. The coefficient of thermal expansion as a body can be adjusted within a desired range.

In the present invention, it is also useful to contain approximately 20% by volume or less of glass powder based on the total amount of the powder aggregate. By containing this glass powder, cracks in ceramic powder and the like can be reliably prevented. Examples of preferred powder aggregates include:
Examples include 40 to 80% by volume of Cu, the remainder Al ₂ O ₃ and/or SiC, or mixtures thereof with borosilicate glass powder of up to about 20% by volume.

In addition, the configuration of the ignition electrode part used in the ignition plug of the present invention is (rather than the central axis as in the conventional case).
The electrode may be formed in the form of a chip (metal electrode) at the tip of a bag-shaped insulator, or the electrode may be sintered onto the insulator itself. The chip-shaped center electrode may have any shape (for example, a stud shape or a T-shape).
A small electrode piece with a vertical cross section or a spherical shape is formed in a small hole at the tip of an insulator bag. Examples of electrode metals include Ni, Ni-based alloys (Ni-Cr, Ni-
Cr-Fe, Ni-Cr-Si, Ni-Si-Cr-Al, Au,
Ag, Au-Ag alloy, Au, Ag or Au・Ag alloy
Pd and/or alloy with Ni, Cr, Ni-Cr, or
Ag-Pt or alloys with Pd and Ir and other known electrode metals can be used. The chip-shaped center electrode can be formed by fitting it into a small hole at the tip of a pre-formed insulator, crimping, welding (fusion), hot pressing, glass sealing, or other known methods. At this time, if necessary, a glass seal is applied to the tip of the tip on the side of the shaft hole 7 or the tip of the shaft hole 7 surrounding the protruding end. The sealing glass should be conductive sealing glass, for example, borosilicate glass 30.
Cu, Ni, Fe, FeB, as metal powder to ~70%
A material containing 70 to 30% of one or more types of NiB powder can be used. Examples of borosilicate glass include B ₂ O ₃ 15-45%, SiO ₂ 40-70%, Al ₂ O ₃ 3-10
% can be used.

In addition, to form the center electrode by integral firing, a small hole 8 is formed at the bag-shaped tip of the press-molded pre-fired insulator 2, the small hole 8 is filled or coated with electrode material, and the insulator 2 is fired at the same time. It is made by firing. The integrally fired electrode material components (hereinafter referred to as approximate weight percentages) are a base of 40 to 60% Pt and 20 to 30% Pd, with 10 to 30% of one or more of TiO ₂ , TiC, and TiN, and the same components as Fe. -Ni-Cr0~3% and
Those containing 0 to 10% of Al ₂ O _{3 C} , and other Ti compounds (TiO ₂ , TiN, TiC) as skeletons and conductivity imparting substances in addition to the above Pt and Pd, Au, Ag, Pu,
A material in which a noble metal such as Rh is dispersed can be used.

In the spark plug of the present invention, the powder aggregate is located next to the center electrodes 3a, 3b, that is, the insulator 2
Although the end portion is filled and formed, the rear end must be sufficiently tightly sealed with electrically conductive sealing materials 6a and 6b so that compressive stress is generated in the metal spherical powder at high temperatures. After satisfying this condition, a known resistor, a self-sealing resistor, or the like may be appropriately disposed.

[Effects of the Invention] According to the present invention, the following various effects can be achieved.

(1) Heat conduction from the ignition part to the terminal shaft direction can be controlled in response to the ignition part temperature, so it has high electrical self-cleaning properties, reliably prevents pre-ignition, and has a wide thermal range. be converted into In this case, by appropriately changing the type and amount of powder, it becomes possible to control the temperature to suit the operating temperature range, and achieve an appropriate wide range.

As a result, the need to change the spark plug depending on the engine model, load condition, season, etc. is reduced, and the always-cleaned ignition section satisfies the optimal conditions for ignition and explosion, making it easier to design the engine.
This is a great advantage in terms of operation and maintenance inspection.

(2) Since ceramic powder is an essential element, it is possible to prevent fusion between the metal spherical powders, and therefore the wide range due to the elastic deformation of the powder can be maintained for a long period of time.

(3) Since the center shaft is no longer required, the spark plug can be made more compact, and the space previously occupied by the center shaft can be effectively utilized.

[Example] Examples of the present invention will be described below.

Example 1 A high alumina press-molded body (raw insulator) having a small hole 8 with a diameter of 1.0 mm and an axial length of 1.5 mm in firing finished dimensions was preliminarily attached to the bag-shaped tip of the insulator 2 shown in Fig. 5. Created. Capacity% as electrode material (same below)
An electrode material paste made by adding an appropriate amount of varnish as an organic binder to a mixed powder of 25% Pt, 25% Pd, 30% TiO ₂ and 20% TiC was filled into the small hole 8, and heated to a temperature of about 1600°C. , fired in the atmosphere to form an insulator 2 having an integrally fired electrode 3a,
Thereafter, the insulator 2 was glazed by a conventional method to obtain an insulator 2 having an inner diameter of the filled part 7 of the powder aggregate (thermal conductor) 4 of 3.6 mm and an inner diameter of the terminal shaft seal part 9 of 4.7 mm.

The lower part of the shaft hole 7 is filled with 0.3g of powder aggregate 4 consisting of 75% Cu spherical powder (20-60 meshes) and 25% Al ₂ O ₃ (30-100 meshes) powder and preloaded at 5-10Kg/ ^cm2. and conductive sealing glass powder 6a on top of it.
(composition _SiO2 65% by weight, _B2O3 30% by weight, _Al2O3 5% by _weight , borosilicate glass powder 50% by _weight and FeB powder 50% by weight)
Fill 0.1g of (wt%) and compact 5-10Kg/cm ²
Made of low carbon steel, preloaded and nickel plated.
A terminal shaft 5 with a diameter of 4.0 mm was inserted. Then 200℃/
The spark plug body 1 was obtained by heating at a temperature increase rate of 10 minutes, maintaining the temperature at 800 to 1000° C. for 10 minutes, and applying a pressure of 16 kg/cm ² to the terminal shaft to hot press.

Example 2 Insulator 2 was obtained in the same manner as in Example 1, except that the small tip hole 8 was not filled with the electrode material paste. Ni alloy or
A stud-shaped electrode chip made of Au/Pd alloy (Fig. 6) containing 50% by weight of Au and the remainder Pd is inserted, and then conductive sealing glass powder 6b (composition: 65% by weight of SiO ₂ , B ₂ O ₃ ) is inserted into the shaft hole 7 side. Borosilicate glass powder (50% by weight of 30% by weight, Al ₂ O ₃ 5% by weight and 50% by weight of FeB powder) was packed and solidified, and further Cu powder (20% by weight) was packed as powder aggregate 4.
~60 mesh) 75% by volume, balance SiC powder (30~100
The spark plug body 1 was obtained in the same manner as in Example 1.

(Comparative Test) The spark plugs according to Examples, Conventional Examples, and Comparative Examples were evaluated for heat resistance and stain resistance based on self-cleaning properties.

The structure of the spark plug is almost equivalent to that shown in FIG. ), a Ni shaft with a Cu core is used, a simple metal spherical powder is used for the comparative example (No. 2), and a powder aggregate is enclosed for the examples (Nos. 3 and 4).

Details of each sample are as follows.

No. 1: Ni center core with Cu core No. 2: Cu spherical powder No. 3: Cu spherical powder and Al ₂ O ₃ powder (25 vol%) No. 4: Cu spherical powder and SiC powder (25 vol%) Also, test The method is as follows.

(a) The heat resistance test was conducted using a 4-cycle, 1800 c.c. engine under the conditions of 5500 rpm x 4/4, varying the ignition advance angle and comparing the pre-ignition occurrence advance angle.

(b) For the self-cleaning test, carbon was attached to the surface of the firing leg of the plug insulator under idling conditions, and carbon was applied 5 mm from the tip of the firing leg of the insulator.
Comparisons were made based on the vehicle speed at which the vehicle turned white (carbon removal). The results are shown in FIG.

As is clear from Figure 7, the self-cleaning property of the conventional metal shaft with a Cu core enclosed is significantly poor, whereas the self-cleaning property of the example is significantly improved with almost the same heat resistance. This makes it possible to achieve a wide range as a whole. In addition, in the comparative sample No. 2, it was difficult to separate the spheres, and the repetition of expansion and contraction was poor.

[Brief explanation of the drawing]

Fig. 1 is a schematic vertical sectional view showing an embodiment of the spark plug of the present invention, Fig. 2 is an enlarged sectional view of the tip of the insulator shown in Fig. 1, and Figs. 3a and 3b schematically show the contact state of powder. FIG. 3a is a graph showing the graph at low temperature, FIG. 3b is graph at high temperature, FIG. 4 is a graph showing the relationship between the amount of heat transfer of the powder aggregate and temperature, and FIG. FIG. 6 is a longitudinal cross-sectional view showing the state before hot pressing of one embodiment, FIG. The figure represents a graph showing the results of comparative tests (self-cleaning and heat resistance). 1...Spark plug, 2...Hollow insulator, 3a,
3b... Center electrode, 4... Heat conductor (powder aggregate), 5... Terminal shaft, 6a, 6b... Seal body (sealing material), 7... Shaft hole (hollow part).

Claims (1)

[Claims] 1. A center electrode is provided at the tip of a hollow insulator, and an aggregate of metal spherical powder and ceramic powder is provided in the hollow part of the insulator and between the center electrode and the terminal shaft. A spark plug characterized in that: the metal spherical powder is elastically deformable in the operating temperature range of the ignition part, and the rear end of the aggregate is sealed with a conductive sealing material.