Electric lamp and discharge devices – Spark plugs – Particular electrode structure or spacing
Reexamination Certificate
2000-12-19
2004-05-04
Patidar, Jay (Department: 2862)
Electric lamp and discharge devices
Spark plugs
Particular electrode structure or spacing
Reexamination Certificate
active
06731052
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a spark plug for internal combustion engines.
SUMMARY OF THE INVENTION
In recent years, there is an increasing demand for a highly durable spark plug for internal combustion engines as the engines become higher in efficiency. Under these circumstances, the durability of the ground electrode is one of the most important problems to be solved. There are two problems with respect to the durability required for the ground electrode. One problem is concerned with the resistance to electrode consumption due to spark discharge. Another problem is concerned with the strength. Namely, there is a problem that transmission of engine vibrations to the ground electrode may possibly cause a crack at the welded portion between the ground electrode and the metallic shell and the progress of the crack may cause the ground electrode to be broken.
With reference to
FIGS. 10A-10C
and
11
A-
11
C, the structure of the ground electrode will be described.
As shown in
FIG. 1A
, a welded portion
16
c
of a ground electrode
16
connected to a front end face
37
of a metallic shell
30
is generally rectangular in cross section and has the maximum width L
1
and the maximum thickness t
1
. As shown in
FIG. 10B
, assuming that M denotes the nominal diameter of an externally threaded portion
31
of the metallic shell
30
, A denotes the outer diameter of the front end face
37
and B denotes the inner diameter of the front end face
37
, a spark plug of 12.00 mm in the nominal diameter M of the externally threaded portion
31
is, for example, 10.10 mm in the outer diameter A of the front end face
37
. In this instance, if the inner diameter B is 7.20 mm, the welded portion
16
c
can be sized to be 1.30 mm in the maximum thickness t
1
and 2.70 mm in the maximum width L
1
. In the meantime, as shown in
FIG. 10B
, a clearance
24
a
is provided between the inner circumferential surface of the metallic shell
30
and the outer circumferential surface of an insulator front end portion
24
.
Herein, as a means for improving the resistance to consumption of the ground electrode
16
, it is considered to expand the maximum width L
1
of the ground electrode
16
and thereby make larger the area of a side surface portion
16
g
facing the center electrode
12
. Further, as a means for making the strength of the ground electrode
16
higher, it is considered to make the maximum thickness t
1
thicker and thereby make the rigidity of the ground electrode
16
higher.
However, if the maximum width L
1
of the ground electrode
16
is made wider and the maximum thickness t
1
is made thicker, the side surface
16
a
including the side surface portion
16
g
facing the center electrode
12
protrudes from the inner circumferential periphery
37
b
of the front end face
37
, and the opposite end corner portions
16
e
of the side surface
16
b
opposite to the side surface
16
a
protrude from the outer circumferential periphery
37
a
of the front end face
37
as shown in FIG.
11
B. To eliminate such protrusion, it is necessary to make the metallic shell
30
thicker and thereby make the area of the front end face
37
larger. In this connection, the width of the front end face
37
can be made larger by making the outer diameter A of the end face
37
large or the inner diameter B smaller. However, increase of the outer diameter A inevitably results in increase of the nominal diameter M of the externally threaded portion
31
of the metallic shell
30
. This disables attachment of the spark plug to the cylinder head, so the outer diameter A cannot be made larger.
If the inner diameter B is reduced, as shown in
FIG. 11C
, from the position indicated by
37
b
to the position indicated by
37
c
, the clearance
24
a
between the inner circumferential surface of the metallic shell
37
and the insulator front end portion
24
will inevitably reduce. By this, sideway jumping of spark due to adherence of carbon onto the surface of the insulator front end portion
24
is liable to be caused, thus causing a problem that the ignition ability is lowered.
It is accordingly an object of the present invention to provide a spark plug for internal combustion engines which can improve the resistance to electrode consumption and the strength of the ground electrode without changing the inner and outer diameters of the end face of the metallic shell.
To accomplish the above object, the present invention provides a spark plug for an internal combustion engine comprising a metallic shell having an externally threaded portion, an insulator disposed in the metallic shell and having an axial bore, a center electrode disposed in the axial bore of the insulator, and a ground electrode connected to a front end face of the metallic shell and having an end opposite to an front end face of the center electrode, wherein a cross section of the ground electrode is so shaped as to provide a side surface at one of opposite sides which faces an outer circumferential periphery of the front end face of the metallic shell, with a narrower central side surface section than that of a side surface at the other of the opposite sides, the central side surface section at one of the opposite sides being parallely opposite to the central side surface section at the other of the opposite sides.
REFERENCES:
patent: 4401915 (1983-08-01), Kashiwara et al.
patent: 4465952 (1984-08-01), Sato et al.
patent: 4970426 (1990-11-01), Bronchart
patent: 5828161 (1998-10-01), Palyu
patent: 6166480 (2000-12-01), Ishida et al.
patent: 0 725 463 (1996-08-01), None
patent: 59-36390 (1984-09-01), None
patent: 8-213149 (1996-08-01), None
patent: 9-129356 (1997-05-01), None
LandOfFree
Spark plug having ground electrode having cross section with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Spark plug having ground electrode having cross section with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spark plug having ground electrode having cross section with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3188500