Electric lamp or space discharge component or device manufacturi – Process – Spark plug or spark gap making
Reexamination Certificate
1999-03-02
2001-12-11
Patel, Ashok (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
Spark plug or spark gap making
Reexamination Certificate
active
06328619
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to equipment and a method for producing spark plugs. More particularly, the present invention relates to an equipment and a method for producing a spark plug including an insulator having an axial through-hole in which a metallic terminal fixed at an end portion thereof and a center electrode fixed at the other end thereof and a sintered conductive material member such as a conductive glass seal layer or a resistor being formed within the through-hole between the metallic terminal, and the center electrode to establish their electrical connection.
2. Field of the Invention
Conventional spark plugs for use in internal combustion engines have built-in resistors with a view to suppressing the generation of noise from electrical waves. Such spark plugs with a built-in resistor includes an insulator having an axial through-hole with a metallic terminal fixed at an end thereof and a center electrode fixed at the other end thereof and the resistor provided in the through-hole between the metallic terminal and the center electrode. A conductive glass seal layer is usually provided between the resistor and the metallic terminal or between the resistor and the center electrode to connect them electrically.
A typical method for producing the spark plug with a built-in resistor is shown in
FIGS. 23A and 23B
. In short, a center electrode
3
is inserted into a through-hole
6
in an insulator
2
and, thereafter, a conductive glass powder, a bulk powder of resistor composition and another mass of conductive glass powder are packed in that order. Finally, a metallic terminal
13
is pressed into the through-hole
6
from the side opposite to the center electrode
3
, thereby making a spark plug assembly. Thus, the through-hole
6
in the insulator
2
contains a conductive glass powder layer
26
therein, a resistor composition powder layer
25
and another conductive glass powder layer
27
that are superposed one on another in that order from the center electrode
3
. The spark plug assembly having this layer arrangement is brought into a heating furnace where it is heated to a temperature higher than the glass softening point. Thereafter, the metallic terminal
13
is uniaxially pushed in from the side opposite to the center electrode
3
, whereby the respective layers
25
to
27
are compressed to form glass seal layers
16
and
17
and a resistor
15
as shown in FIG.
23
B.
In the above-described method for the production of spark plugs with a built-in resistor, the individual layers are compressed by a so-called “one-side press” method. Namely, the metallic terminal
13
is pushed in toward the center electrode
3
with the position of the latter fixed. In this case, the conductive glass powder layer
26
located in the lowest position in
FIG. 23A
does not receive a sufficient pressing force due to the friction between the overlaying packings and the inner surface of the through-hole
6
. Accordingly, the compression or flow of the powder is inhibited, sometimes causing poor sintering of the glass seal layer
16
on account of its low density. If this situation occurs, the carbon in the glass seal layer
16
is burnt away or the metallic component is oxidized. As a result, the electrical continuity between the resistor
15
and the center electrode
3
via the glass seal layer
16
becomes imperfect and as the use of the spark plug is prolonged. It may be that the conduction resistance increases to potentially cause occasional misfiring.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an equipment for producing a spark plug by the “one-side press” method with the metallic terminal pushed toward the center electrode but with a smaller possibility for the occurrence of poor electrical connection between the metallic terminal and the center electrode via the conductive glass seal layer(s), the resistor and any other intervening elements.
It is another object of the present invention to provide a method for producing spark plugs using the equipment. According to the present invention, the equipment and the method for producing a spark plug which comprises an insulator, a metallic terminal, a center electrode and a conductive material. In the insulator, a through-hole is formed in an axial direction of the insulator. The metallic terminal is fixed at one end of the through-hole. The center electrode fixed at the other end of the through-hole. A sintered conductive material member comprising a mixture of glass and a conductive material being formed within the through-hole between the metallic terminal and the center electrode for connecting the metallic terminal and the center electrode electrically.
The equipment has a heating device for heating a spark plug assembly comprising an insulator in which a through-hole is formed in an axial direction of the insulator, a metallic terminal fixed at one end of the through-hole, a center electrode fixed at the other end of the through-hole and a packing layer of a bulk powder of the sintered conductive material member being formed in the through-hole between the metallic terminal and the center electrode so that the packing layer of the bulk powder begins to soften from the center electrode side along the longitudinal axis of the insulator.
In the equipment, the spark plug assembly is heated by the heating device so that the temperature of the center electrode side is higher than that of the metallic terminal side along the axial direction of the insulator.
The method for producing a spark plug comprises: preparing a spark plug assembly having a metallic terminal fitted at an end of the through-hole in the insulator and a center electrode fitted at the other end thereof and a packing layer of a bulk powder of the sintered conductive material member being formed in the through-hole between the metallic terminal and the center electrode; heating the spark plug assembly so that the layer packed with the bulk powder begins to soften from the center electrode side along the axis direction of the insulator; and pressing the packing layer of the bulk powder within the through-hole between the center electrode and the metallic terminal by applying pressure to the heated spark plug assembly so that the metallic terminal comes closer to the center electrode along the axis of the through-hole with the position of the center electrode being fixed relative to the through-hole.
If the spark plug assembly is heated such that the packing layer of the bulk powder begins to soften from the center electrode side along the longitudinal axis of the insulator, the softening of the glass in the packing layer will be subjected at a faster rate on the side closer to the center electrode along the axis of the packing layer than on the side closer to the metallic terminal. If the packing layer is pressed by the so-called “one-side press” method, with pressure applied from the metallic terminal side toward the center electrode side along the longitudinal axis, even the bulk powder on the center electrode side which is resistant to the propagation of applied pressure undergoes a smaller flow resistance due to the progress of glass softening and can be compressed as efficiently as the bulk powder on the metallic terminal side. As the result, the sintered conductive material member is efficiently compressed and sintered not only on the metallic terminal side but also on the center electrode side, thus ensuring satisfactory electrical connection to be established at all times between the sintered conductive material member and the center electrode.
One way to soften the packing layer of the bulk powder from the center electrode side along the axis of the insulator is by heating the spark plug assembly such that its center electrode side has a higher temperature than the metallic terminal side to ensure preferential softening or melting of the glass in that part of the packing layer of the bulk powder which is located on the center electrode side. Another way is
Shimizu Kenji
Tanaka Yutaka
Hopper Todd Reed
Morgan & Lewis & Bockius, LLP
NGK Spark Plug Co. Ltd.
Patel Ashok
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