JPH0115992B2 - - 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. However, 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 ceramic coating in the hollow part of the insulator between the center electrode and the terminal shaft. An aggregate made of metal spherical powder is present, the 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. shall be.

[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 with 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 a simple metal spherical powder is greater than that of a ceramic-coated metal spherical powder or a ceramic powder.

In addition, since a ceramic coating is an essential element for powder aggregates, it prevents the powders from becoming integrated due to fusion, etc. (compared to aggregates made only of metal spherical powders), 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 needs to have an appropriate coefficient of expansion within a set temperature range, stay in an elastic region, have stability as the temperature drops, and 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, the above metal spherical powder coated with ceramic is an essential element. This ceramic coating may be an oxidized coating made by heat-treating metal spherical powder in the atmosphere, or an oxidized coating made by heat-treating metal spherical powder in the atmosphere, or Al ₂ O ₃ , TiO ₂ ,
Oxides such as ZrO ₂ and SiO ₂ , TiC, SiC, Mo ₂ C,
Preferably, the coating is made of a carbide such as B ₄ C, a nitride such as AlN, BN, TiN, ZrN, or a silicide such as MoSi ₂ or TiSi. In this case, mixed or layered coatings of these are also possible. In addition, ceramic coatings made of carbides and silicides have conductivity in themselves, and ceramic coatings made of Al ₂ O ₃ etc., which do not have conductivity in themselves among oxides and nitrides, If so, it is best to form a thin film (in some cases, create microcracks) to ensure conductivity between the metal spherical powders.

The powder aggregate may be at least partially made of metal spherical powder coated with ceramic. That is, the powder aggregate may consist only of ceramic-coated metal spherical powder, or it may be a mixture of ceramic-coated metal spherical powder and mere (non-ceramic-coated) metal spherical powder. .

The formation of ceramic coatings is for example
500μ of Cu powder is heat-treated at 500℃ for 1 hour to form an oxide film on the surface of the metal sphere, or immersed in a ceramic raw material solution or slurry and then heat-treated and baked, or by chemical vapor deposition, etc. This can be done by a known method.

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, it is possible to reliably prevent cracks in metal spherical powder having a ceramic coating. Examples of preferred powder aggregates include 40-80% by volume of Cu, balance _Al2O3 and/or SiC, or these mixed with up to about 20% by _volume of borosilicate glass powder.

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 and other Ti compounds (TiO ₂ , TiN, TiC) as skeletons and conductivity-imparting substances in addition to the above Pt and Pd, such as 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 includes the insulator 2 next to the center electrodes 3a and 3b.
Although the bag-shaped tip is filled and formed, the rear end must be sealed sufficiently firmly with 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 the metal spherical powder having a ceramic coating is an essential element, it is possible to prevent the metal spherical powder from adhering to each other, 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 air under zero atmosphere to form an insulator 2 having an integrally fired electrode 3a,
Thereafter, the insulator 2 was glazed in a conventional manner 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 0.3 g of powder aggregate 4 made by heat-treating Cu spherical powder (20 to 60 meshes) at 500°C for 1 hour, preloaded at 5 to 10 kg/cm ² , and a conductive layer is placed on top of it. Seal glass powder 6a (composition SiO ₂ 65
(wt%, _B2O3 30wt%, _Al2O3 5wt _% , borosilicate glass powder 50wt _% and FeB powder 50wt%)
Fill with 0.1g, compact and preload with 5-10Kg/ ^cm2 .
Made of low carbon steel with nickel finish, diameter 4.0mm
Terminal shaft 5 was inserted. Then, heat at a temperature increase rate of 200℃/min and hold at 800 to 1000℃ for 10 minutes.
A pressure of Kg/cm ² was applied to the terminal shaft and hot pressed to obtain a spark plug body 1.

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. Tip small hole 8 is made of 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.
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 to 5).

Details of each sample are as follows.

No. 1: Ni core with Cu core No. 2: Cu spherical powder No. 3: Cu spherical powder coated with oxidation No. 4: Cu spherical powder coated with TiN No. 5: Cu spherical powder coated with TiN and Cu spherical powder (50vol%).The test method is as follows.

(a) The heat resistance test was conducted using a 4-cycle, 1800c.c. engine under the conditions of 5500rpm x 4/4, varying the ignition advance angle and comparing the preignition 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 conventional example with a metal shaft containing a Cu core has significantly poor self-cleaning performance, whereas the example example has significantly improved self-cleaning performance 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 drawings]

Fig. 1 is a schematic longitudinal 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 having a ceramic coating is provided in the hollow part of the insulator between the center electrode and the terminal shaft. The 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.