JPS6144391B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a closed-end porcelain spark plug installed in an internal combustion engine. [Prior Art] The electrode firing part of a spark plug is constantly exposed to a maximum temperature of nearly 1000°C in the combustion chamber, and must not only be able to withstand this temperature, but also have consumable resistance against spark discharge and chemical durability against combustion gas. However, the conditions of use are extremely harsh. Conventionally, platinum and gold-based metals have been known to have excellent properties as center electrode materials, and wires of noble metals such as platinum, palladium, gold, and silver are used in some special products. However, since these are expensive, heat-resistant alloys mainly made of nickel are generally used. When a spark plug mainly made of nickel alloy is used for a long period of time, the electrode firing part wears out and the spark gap between the electrodes expands, causing the spark discharge voltage to become higher than the voltage generated by the power supply and no longer discharging. . In order to improve this drawback and increase the durability of the spark plug, the center electrode is wrapped in an insulator.
A closed-end porcelain spark plug has been proposed in which the tip ignition part is made conductive and has a cermet electrode. [Problems to be Solved by the Invention] The above-mentioned cermet electrode can be used as an alternative to the conventional metal wire electrode, depending on the composition and manufacturing conditions.
Although it is quite heat resistant and wear resistant, the inventors installed a closed-end porcelain spark plug with a cermet electrode (for example, a mixture of platinum powder and sintered alumina powder) on the engine. When tested at high temperature and over a long period of time, it was discovered that the metal on the outer edge of the electrode's surface first melted, and then the outer edge surface began to wear out, which led to the electrode peeling off. This is because the outer edge is less uniform and dense than the center, so the metal is isolated and heat conduction is poor.The outer edge has poor conduction and cooling of combustion heat to the electrode side, causing abnormal heating. This is thought to be because it occurs. The present invention aims to solve these problems and provide a closed-end porcelain spark plug whose electrodes can be sintered densely and firmly and which has excellent durability against spark discharge and combustion heat. [Means for Solving the Problems] The closed-end porcelain spark plug of the present invention is made of oxide ceramics such as Al ₂ O ₃ , TiO ₂ , Cr ₂ O ₃ , ZrO ₂ ,
SiO ₂ , Y ₂ O ₃ or La ₂ O ₃ powder, carbide ceramics TiC, SiC, B ₄ C or Cr ₃ C ₂ powder, nitride ceramics TiN, AlN or BN.
Mixed sintering of one or more of the powders of _MoSi2 , which is a silicide ceramic, and one or more of the powders of metals, such as Fe, Ni, Cr, Co, Mo, Mn, Pt, or Pd. A cermet electrode whose body is formed to seal a hole at the tip facing an outer electrode of a porcelain insulator having a conductive shaft inside, and a cermet electrode adhered to the surface of the cermet electrode. The structure includes a center electrode made of a ceramic protective layer. [Example] Next, the present invention will be described based on an example shown in the drawings. 1 is a metal shell having an outer electrode 4 protruding from one end and a mounting screw provided on the outer periphery; 2 is a metal shell 1;
An insulator made of ceramics mainly composed of alumina and provided with a shaft hole 3 constituting the center electrode shaft inside, 5 is an insulator 2 facing the outer electrode 4.
This is a cermet electrode filled in a tip hole 3a provided at the tip of a shaft hole 3. This cermet electrode 5 is made of a mixture of the following:
It is buried in the tip hole 3a of the insulator 2, and is sintered together with the insulator 2. One or more of the following ceramic powders 1, 2, 3, or 4: 1...Al ₂ O ₃ , TiO ₂ , Cr ₂ O ₃ , ZrO ₂ , SiO ₂ , Y ₂ O ₃
or oxide of La ₂ O _{3 2} ... Carbide of TiC, SiC, B ₄ C or Cr ₃ C _{2 3} ... Nitride of AlN, BN or TiN 4... Silicide of MoSi ₂ Among the following 5 which are metal powders One or more of the following: 5...Fe, Ni, Cr, Co, Mo, Mn, Pt, or Pd 6 is a ceramic protective layer firmly adhered to the surface of the cermet electrode 5. The materials for the ceramic protective layer 6 used here include alumina (Al ₂ O ₃ ), mullite (3Al ₂ O ₃ .2SiO ₂ ), zirconia (ZrO ₂ ), spinel (MgO.SiO ₂ ), and zircon (ZrO _{2 )} . -SiO ₂ ) or titania (TiO ₂ ) can be suitably used. As shown in FIG. 2, this protective layer 6 is formed by filling the tip hole 3a of the alumina green base insulator 2 with a cermet electrode 5 material, and further covering the surface of the electrode 5 with the protective layer 6 in the form of a slurry. After coating with the layer material, this is formed by co-sintering with the insulator 2. The thickness of the coating film is such that it is easily penetrated and destroyed by the high voltage of spark discharge. The protective layer 6 can also be coated on the electrode surface of an insulator obtained by simultaneously sintering the green insulator 2 and the cermet electrode material 5 together by thermal spraying with plasma or the like. Although this sprayed layer is not very dense and porous, it still protects the electrode and reduces spark consumption. Furthermore, 7 is a conductive sealing material, which is made of conventional metal powder {Cu: 50%, balance SiO ₂ : 65%, B ₂ O ₃ : 30
%, Al ₂ O ₃ : 50% borosilicate glass}, and 8 is a resistor containing 40 parts by weight of borosilicate glass with the same composition ratio, 30 parts by weight of zircon powder, and Si ₃ N ₄ powder.
It is a resistor powder consisting of 30 parts by weight and 2 parts by weight of methyl cellulose, and a conductive sealing material 7 is placed in the shaft hole 3 provided with the electrode 5 of the insulator 2, or an appropriate amount of the resistor 8 is added to the conductive sealing material 7. Filled and heated to 800~1100℃
This is a spark plug in which the metal terminal shaft 9 is sealed by heating and then assembled into a metal shell according to customary specifications. Table 1 shows the results of a 100-hour durability test of the closed-end porcelain spark plug of the present invention. This durability test was performed using a 2000 c.c. engine for 100 hours at a rotational speed of 5000 rpm and a load of 4/4 (full throttle opening), and was expressed as the rate of increase in discharge pressure. The results are shown in Table 1. The discharge pressure of the conventional spark plug of sample 1 increased by 100% from the value before the durability test, and the consumption of the electrode material increased, whereas the discharge pressure of the conventional spark plug of sample 1 The discharge pressure of the closed-end porcelain spark plug of the present invention was suppressed to an increase rate of 70% or less compared to the P value before the durability test, and the effect of reducing consumption of the electrode material was confirmed (*
(indicates a cermet electrode formed during firing in a reducing atmosphere).

【table】

[Table] [Effects of the Invention] The closed-end porcelain spark plug of the present invention has the following effects. Since the surface of the cermet electrode is protected by a ceramic protective layer, the cermet electrode is not damaged by spark discharge and has good durability. (a) Since the discharge surface is covered with ceramics, it does not come into direct contact with highly oxidizing combustion gas, which has the effect of increasing the chemical durability of the cermet electrode against combustion gas. C. Since the discharge is limited to a certain area, the discharge resistance increases, which is also advantageous in preventing radio noise caused by the discharge.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a closed-end porcelain spark plug according to the present invention, and FIG. 2 is a cross-sectional view of a main part of the closed-end porcelain spark plug according to the present invention. In the figure, 1...metal shell,
2... Insulator, 3... Shaft hole, 3a... Tip hole, 4... Outer electrode, 5... Cermet center electrode, 6... Ceramic protective layer.

Claims (1)

[Claims] 1 (a) (a) Al ₂ O ₃ which is an oxide ceramic,
_TiO2 , _{Cr2O3 , ZrO2} , _SiO2 , _{Y2O3 or}
La ₂ O ₃ powder, carbide ceramics TiC, SiC,
B ₄ C or Cr ₃ C ₂ powder, nitride ceramic TiN, AlN or BN powder, and silicide ceramic MoSi ₂ powder, and (b) metals F and Ni. , Cr, Co, Mo, Mn,
A mixed sintered body of one or more of Pt or Pb powder and is provided so as to seal a hole provided at the tip facing the outer electrode of a porcelain insulator having a conductive shaft inside. (b) a ceramic protective layer deposited on the surface of the cermet electrode; 2. The ceramic protective layer comprises alumina, mullite, zirconia, spinel, A closed-end porcelain spark plug according to claim 1, characterized in that it is made of one or more ceramic materials selected from zircon and titania.