JPH0298085A - Spark plug - Google Patents

Abstract

PURPOSE:To obtain a cheap and mass-production allowable spark plug with heater by using coat powder coated with precious metal for the heating resistor and the electrode ejected portion of a heater to eliminate burning in a hydrogen atmosphere. CONSTITUTION:When heater material coated with precious metal on the surface of tungsten is used, tungsten is not oxidated even if burned in an alumina oxodating atmosphere at 1600 deg.C or so. Coating alumina with precious metal realizes property as in cermet and allows resistivity to be changed arbitrarily with changed thickness of coating. In case of platinum ink among precious metals, the problem happens that low or high burning temperature causes dispersion of a resistance value due to growth and disorganization of platinum grains, however, control of the dia. of the aluminum grain and the thickness of aluminum coating leads to lower effect. In addition, for single or continuous occurrence of firing electrode made of precious metal, etc., simultaneously burning of an electrode, an intermediate-electrode of conductive ceramics, a heater and an insulator attain simplified burning and greatly reduced cost.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a spark plug for an internal combustion engine, and more particularly to a spark plug in which a heater is integrally connected to the outer periphery of a long leg portion of an insulator.

<Conventional technology> Conventionally, in order to prevent carbon from smoldering and contaminating the spark plug, a ceramic heater has been integrated into the outer periphery of the leg section of the insulator exposed to the combustion chamber. is known to burn out and restore insulation resistance.

<Problems to be Solved by the Invention> By the way, the heating resistor materials of conventional ceramic heaters are mainly materials that are easily oxidized but have a high melting point, such as tungsten and molybdenum, or materials that are difficult to oxidize and have a high melting point, such as platinum. However, since the former is fired in a hydrogen atmosphere, the firing cost is high, it is not suitable for mass production, and the original mechanical performance of alumina is impaired. Since the latter method is fired in the atmosphere, the firing cost is low, but the material cost is high.

The purpose of the present invention is to perform the firing of the heater and insulator in a completely oxidized ambient atmosphere, which reduces the firing cost and facilitates mass production.
To provide a nine-spark plug equipped with a heater on the outer periphery of the long leg part of an insulator, which can sufficiently provide the performance of L'Mina.

The present invention provides a spark plug in which a ceramic heater is integrally connected to the outer periphery of the long leg portion of an alumina insulator.
This spark plug is characterized in that the main component of the heater material is a coating made by coating the surface of tungsten powder or alumina powder with a noble metal having a melting point of 1600"C or more, and the material is alumina powder gold in the coating powder. In addition, the ignition electrode arranged at the tip of the insulator is made of a noble metal having a melting point of 1600'C or higher or coated powder of a heater, and is formed by firing the heater and the insulator together. [This is a spark plug in which the intermediate electrode connected to the FM is made of conductive ceramic and is similarly fired together with the heater and the insulator.

Effects> When the spark plug of the present invention having the above structure is used with the heater material being tungsten coated with a noble metal, the following effects can be achieved:
Tungsten oxidation does not occur even under firing conditions of an oxidizing atmosphere of alumina at around 600°C. The constant resistance value can be adjusted by adjusting the total amount of alumina powder added. On the other hand, alumina coated with a noble metal has cermet-like characteristics, and the specific resistance can be changed arbitrarily by changing the thickness of the coating. Furthermore, in the case of platinum ink among noble metals, there was a problem of variation in resistance due to grain growth and coarsening of platinum particles due to low and high firing temperatures, but this can be suppressed by controlling the alumina particle size and platinum film thickness. Can be done. Furthermore, single or group ignition N of ignition electrodes such as noble metals,
Co-firing the pole, the conductive ceramic intermediate electrode, the heater, and the insulator simplifies the firing process and greatly reduces costs.

Embodiments> The spark plug of the present invention will be described below with reference to embodiments shown in the drawings.

FIG. 1 is a front half-sectional view of the spark plug of the present invention.
is an insulator made of alumina, 2 is a combustion chamber electrode, and 4 points are ignited 1! Bonded on top of the pole 3 is an intermediate consisting of a conductive ceramic such as MoSi2. [M, 5 is sealed with a known conductive glass sandwiching the resistor 6, and is a terminal! It is heat-sealed together with ff17 inside the shaft hole. 8 is a ceramic heater wound around the outer periphery of the long leg portion 2; the heater has an electrode lead-out portion 9, a body portion 11 of the insulator 1;
The ring electrodes 13 and 14 are connected to an annular groove exposed in the exposed portion 12 at the rear end, and a voltage is applied using a power source and a control device (not shown). .

Reference numeral 15 denotes a main metal fitting, and an engine mounting screw 16 is inserted into the inner cavity thereof, and the insulator 1 is fixed to the crotch seat through a gasket "17" and the rear end edge 18 is fixed by a known method of caulking. This is a spark plug in which an outer 'F!L pole 19 is provided protrudingly and a spark gap is formed between it and the ignition fFM3.

The manufacture of the above spark plug will be described.

Example 1 A noble metal (Pt, Rh) having a melting point of 1600° C. or higher is added to tungsten primary particles (average grain size 1 μm).

Coated powder whose entire surface is coated with In) and alumina powder (
A tungsten paste made by blending a tungsten paste (with an average grain size of 1 μm), a solvent, and a dispersant is pasted on an alumina green sheet 20 by screen printing, etc., as shown in Figure 2, and the heating resistor 21 and electrodes are taken out. parts 9 and 10 are formed, press-formed and ground to a predetermined size, and then wrapped around the recess of the long leg part 2 of the fixed link body 1 with the heating resistor inside, and the gap at both ends is filled with alumina paste. . Next, for the electrode extraction parts 9 and 10 on the insulator side, a paste of noble metal coating powder is used on the tungsten, and a pair of annular grooves are provided in the axial groove 22 and the exposed part 12 of the side leg part 114C of the insulator. At the same time, the axial groove 22 is filled with aluminium oxide, and the paste is left exposed in the radial slit 7t. This insulator is fired at 1600° 0 (MAX temperature) in an air atmosphere. Ring electrodes ia and i4 are joined to the radial groove. In the shaft hole of this insulator 1, a copper core is sealed inside like a general spark plug, and a center electrode of a nickel alloy electrode is inserted, and a conductive gaff 5 and a resistor 6 are inserted in the upper part.
After the terminal electrode 7 is heat-sealed, it is assembled to the metal shell 15 with a constant spark defogger.

In addition, for the center electrode, a Pt+Ir, Pt-Ir alloy wire or coated powder for a heater is formed into a rod shape and fired, and the center electrode is made of a hole. After that, this is placed in the shaft hole of the insulator before being completely fired, and the heater 8 and the insulator are simultaneously fired to form the ignition electrode 3 and the intermediate electrode 4f! The two may be integrally formed. The ignition electrode 3 and heater 8 are fired simultaneously with the insulator 1, and then the intermediate WLF! As A, the pole 4 may be joined to an intermediate member made of a metal rod such as Cobar μ, and the conductive glass 5, the resistor 6, the terminal M, and the pole 7 may be heat-sealed together.

Note that the tungsten paste used for the heater 8 may be oxidized when fired in the air depending on the thickness of the platinum film, so care must be taken in the method of preparing the paste. Also, it is better to reduce the addition of alumina powder, which reduces the resistance of the wL electrode extraction part.

Example 2 For the heat-generating resistor and electrode lead-out portion of a heater, primary particle powder of alumina is coated with the same noble metal having a melting point of 1600° C. or higher, and a coated powder is used. If the thickness of the coating is 1 μm or more, the specific resistance will be on the order of mΩ, which is not preferable, so the thickness is set to 1 μm or less.

Alternatively, the resistance ffl may be adjusted by adding 1 to 20% by weight of co-base alumina to the coat powder as in Example 1 above. The other manufacturing methods are the same as those of the first embodiment, so the explanation will be omitted.

Next, the results of fouling using the spark plug equipped with the heater of the present invention shown in FIG. 1 will be described.

The results 1 & of a vehicle equipped with a 20QOCC 6-cylinder engine under test conditions of 90 seconds of idling at room temperature of -10'C and repeated pattern operation of 120 seconds of 15-40Ax/H vehicle speed as one cycle are shown in Figure 3. As shown in the figure, the insulation resistance decreased to IOMΩ in 5 cycles, so after 5 cycles ρ, the heater was energized (IOW - 9V) for 1 minute, and from the 6th cycle onwards, the ignition ON time < heat p-ic energization (1
0W-9V), the insulation resistance was able to be restored to oo.

In this way, the insulation resistance can be restored to normal by energizing the heater for a certain period of time during low-speed running or after running for a certain period of time.

<Effects of the Invention> As described above, the heater-equipped spark plug of the present invention coats the dust-generating resistor and the electrode lead-out portion of the heater with a precious metal, and uses alumina powder, which is expensive in terms of cost. This eliminates the need for firing in a hydrogen atmosphere, which completely deteriorates the mechanical properties of the spark plug, making it possible to manufacture a spark plug with a heater that is suitable for mass production at low cost, and easily restores insulation resistance to normal when the plug smokes. It is possible to easily obtain tomogufugu with excellent stain resistance.

[Brief explanation of drawings]

FIG. 1 is a front half-sectional view of a spark plug showing an embodiment of the present invention, and FIG. 2 shows a seat of a ceramic heater, in which (a) shows a case of series connection and (b) shows a case of parallel connection. FIG. 8 is a graph showing the results of a contamination test in which the spark plug of the present invention was fully bent. 1... Insulator 2... Long leg portion 3... Firing electrode
4...GIJl[i 8...Ceramic heater
9, 10... Electrode extraction part 20... Green sheet 21... Heating resistor patent applicant NGK Spark Plug Co., Ltd.

Claims (4)

[Claims] (1) In a spark plug in which a ceramic heater is integrally bonded to the outer periphery of the long leg portion of an alumina insulator, the material of the heater's heating resistor and electrode lead-out portion is such that the main component thereof is tungsten powder or alumina powder on the surface. A spark plug characterized in that it is made of coated powder coated with a noble metal having a melting point of 1600°C or higher. (2) The spark plug according to claim 1, wherein the material is a mixture of coat powder and alumina powder. (3) In the spark plug according to the above claims (1) and (2), the ignition electrode disposed at the tip of the insulator has a diameter of 1600 mm.
1. A spark plug characterized in that it is made of a noble metal having a melting point of at least °C or coated powder of a heater, and is formed by simultaneously firing a heater and an insulator. (4) The spark plug according to claim 3, wherein the intermediate electrode coupled to the ignition electrode is made of conductive ceramic and is formed by co-firing with the heater and the insulator.