Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Silicon controlled rectifier ignition
Reexamination Certificate
2000-03-08
2001-05-01
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Silicon controlled rectifier ignition
C313S118000, C313S137000, C313S145000, C123S1690EL, C123S594000
Reexamination Certificate
active
06225752
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spark plug for use as an ignition source of an internal combustion engine, and more particularly to a semi surface discharge type spark plug having a structure that the igniting surface of a ground electrode is disposed opposite to the outer surface of a central electrode.
2. Description of the Related Art
Hitherto, a semi surface discharge type spark plug having a structure shown in
FIGS. 14 and 15A
to
15
C is known.
FIG. 14
is a partial cross sectional view of the semi surface discharge type spark plug.
FIG. 15A
is a cross sectional view showing a leading end portion (a spark discharge portion) of the semi surface discharge type spark plug shown in FIG.
14
.
FIG. 15B
is a diagram showing a different-diameter portion (a gap) formed between a leading end
24
e
of an elongated leg portion
24
shown in FIG.
15
A and an outer surface
12
a
of a central electrode
12
.
FIG. 15C
is a diagram showing the thickness of the leading end
24
e
of the elongated leg portion
24
shown in FIG.
15
A.
Note that description will now be made such that the lower portion shown in
FIG. 14
is the leading end portion and the upper portion is the rear end portion.
The semi surface discharge type spark plug
10
is provided with an insulating member
20
made of alumina or the like. The insulating member
20
incorporates a corrugation portion
22
formed in the rear end portion thereof and an elongated leg portion
24
formed in the front end portion and formed into a pyramidal shape. The insulating member
20
has an axial hole
26
formed along a central axis
18
of the insulating member
20
. A terminal
13
is accommodated in a rear end portion in the axial hole
26
. The rear end of the terminal
13
projects over the rear end of the corrugation portion
22
. The central electrode
12
is, through a glass resistance
11
, accommodated in the axial hole
26
at a position adjacent to the terminal
13
. The central electrode
12
is formed into a rod shape and made of an alloy mainly composed of nickel. A front surface
12
f
of the central electrode
12
projects over the leading end of the elongated leg portion
24
of the insulating member
20
.
The leading end of the insulating member
20
is accommodated in a main metal shell
14
formed into a cylindrical portion. A leading end
24
e
of the elongated leg portion
24
projects over an opened front surface
14
c
of the main metal shell
14
. A packing member
17
is disposed between the rear end of the elongated leg portion
24
and the main metal shell
14
. A male thread portion
14
a
arranged to be screwed in a female thread portion provided for a cylinder head of an engine is formed around the leading end of the main metal shell
14
. A base portion
16
b
of each of ground electrodes
16
is secured to a front surface
14
c
of the main metal shell
14
.
Each of the ground electrodes
16
is bent into an L-like shape facing the central axis
18
. An igniting surface
16
a
at the leading end of each of the ground electrodes
16
is disposed opposite to the outer surface
12
a
of the central electrode
12
so that an igniting portion SG is formed between the igniting surface
16
a
and the outer surface
12
a
(see FIG.
15
A). As shown in
FIG. 15A
, a first gap g
1
is formed between the outer surface
12
a
of the central electrode
12
and an igniting surface
16
a
of the ground electrodes
16
. A second gap g
2
is formed between the outer surface of the leading end
24
e
of the elongated leg portion
24
and the igniting surface
16
a.
As shown in
FIG. 14
, a hexagonal portion
14
b
is formed at the rear end of the main metal shell
14
to permit a tool, such as a plug wrench, to be fit to the hexagonal portion
14
b
when the male thread portion
14
a
is screwed in a female portion provided for the cylinder head of the engine.
The thermal expansion coefficient is different between the central electrode
12
made of metal and the insulating member
20
made of alumina ceramic. Therefore, there is difference in the thermal expansion between the two elements. To prevent a fracture of the insulating member
20
, a different-diameter portion (a gap)
15
is formed between the outer surface
12
b
of the central electrode
12
and the axial hole
26
, as shown in FIG.
15
B.
As shown in
FIG. 15C
, an intersection is formed between an extension line
60
a
drawn by outwards extending a line
60
indicating a side surface
24
f
of the elongated leg portion
24
adjacent to the igniting portion and an extension line
61
a
drawn by extending a line
61
indicating a side surface
24
c
of the elongated leg portion
24
toward the side surface
24
f
of the igniting portion. The distance (hereinafter called a “thickness”) tp from the intersection to a line
65
indicating the inner surface of the axial hole
26
is 1.1 mm. Gap ga of the second gap g
2
is 0.5 mm. Length (the axial directional distance from the side surface
24
f
of the elongated leg portion
24
to a sealing surface
24
g
to which the packing member
17
is joined, as shown in
FIG. 14
) L of the elongated leg portion
24
is 12 mm. The difference (hereinafter called the “difference &Dgr;&phgr;d in the diameter”) between diameter &phgr;d
1
of the central electrode
12
and diameter &phgr;d
2
of the axial hole
26
is 0.09 mm. Distance &Dgr;&phgr;d/2 of the different-diameter portion
15
is 0.09 mm/2=0.045 mm.
The male thread portion
14
a
of the main metal shell
14
is screwed in the female portion of the cylinder head. Thus, the semi surface discharge type spark plug
10
structured as described above is joined to the cylinder head such that the ground electrodes
16
, the leading end
24
e
of the elongated leg portion
24
and the leading end of the central electrode
12
are exposed to the inside portion of the combustion chamber of the engine. Then, a high electric resistance cable is connected to the terminal
13
. When discharge voltage is applied, a spark is ignited between the igniting surface
16
a
of the ground electrodes
16
and the central electrode
12
. Thus, mixture in the combustion chamber is ignited.
The cleanability of a spark made by the spark plug for an internal combustion engine will now be described with reference to
FIG. 16
which shows the principle of the cleanability.
As shown in
FIG. 16
, the discharge voltage is applied such that the central electrode
12
has negative polarity and the ground electrodes
16
has positive polarity. Therefore, the elongated leg portion
24
is charged with the positive polarity owing to dielectric polarization. Hence it follows that negatively-charged particles contained in the spark made at the end
12
g
of the central electrode
12
is attracted to the side surface
24
f
of the elongated leg portion
24
. Therefore, the negatively-charged particles reach the igniting surface
16
a
of the ground electrodes
16
through a discharge passage formed along the side surface
24
f
of the elongated leg portion
24
, as indicated with symbol S shown in FIG.
16
.
Therefore, conductive fouling substances allowed to adhere to the side surface
24
f
of the elongated leg portion
24
owing to fouling are burnt out by the spark.
That is, fouling resistance of the semi surface discharge type spark plug having the above-mentioned spark cleanability is superior to that of an aerial discharge spark plug.
Problems to be Solved by the Invention
When sparks frequently move along the side surface
24
f
of the elongated leg portion
24
, the energy of the spark causes the side surface
24
f
to be consumed. Thus, a groove
24
k
(see
FIG. 16
) is sometimes formed. That is, so-called “channeling” sometimes occurs. When channeling proceeds, a through portion is formed in a portion of the elongated leg portion
24
adjacent to the discharge passage S. As a result, a fracture of the elongated leg portion
24
occurs or heat resistance deteriorates. That is, there is apprehension that the durabi
Kokubu Akio
Matsubara Yoshihiro
Yamaguchi Makoto
Yoshida Kazumasa
Morgan & Lewis & Bockius, LLP
NGK Spark Plug Co. Ltd.
Philogene Haissa
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