Information
-
Patent Grant
-
6642638
-
Patent Number
6,642,638
-
Date Filed
Tuesday, July 10, 200123 years ago
-
Date Issued
Tuesday, November 4, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Patel; Nimeshkumar D.
- Colón; German
Agents
-
CPC
-
US Classifications
Field of Search
-
International Classifications
-
Abstract
An improved structure of a spark plug is provided for improving heat dissipation from an Ir-alloy chip attached to a ground electrode. The Ir-alloy chip works to a sequence of sparks between itself and the tip of a center electrode mounted in a metal shell and is embedded in a center electrode-facing surface of the ground electrode, thereby enhancing the transmission of heat produced in the Ir-alloy chip to the metal shell through the ground electrode.
Description
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to a spark plug which may be employed in automotive vehicles, gas pumps and cogeneration systems, and more particularly to a spark plug with a ground electrode having installed therein an Ir-alloy chip.
2. Background Art
Japanese Patent First Publication No.
8-298178
discloses a spark plug equipped with an Ir-alloy chip. The spark plug includes a center electrode and a ground electrode. The center electrode is disposed within a metal shell through a porcelain insulator and has a tip exposed outside an end of the metal shell. The ground electrode is joined to the end of the metal shell and has a spark discharging surface formed on an end thereof which defines an air gap (also called a spark plug gap) between itself and the tip of the center electrode. The Ir-alloy chip is installed on the spark discharging surface of the ground electrode for producing a sequential of sparks between itself and the end of the center electrode.
When the spark plug is used in an internal combustion engine, the Ir-alloy chip is subjected to intense heat. The heat principally dissipates from the Ir-alloy chip to the ground electrode and to the metal shell and the atmosphere. The Ir-alloy chip is bonded to the surface of the ground electrode through a corrosion resisting non-noble metallic member. Specifically, the whole of the Ir-alloy chip lies over the surface of the ground electrode. This structure, therefore, arrests the transmission of heat from the Ir-alloy chip to the ground electrode, so that the Ir-alloy chip is exposed to intense heat for a long time, resulting in acceleration of oxidation and wear of the Ir-alloy chip.
SUMMARY OF THE INVENTION
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide a spark plug with an Ir-alloy chip joined to a ground electrode which is designed to provide a desired amount of heat dissipation from the Ir-alloy chip.
According to one aspect of the invention, there is provided a spark plug which may be employed in automotive vehicles, gas pumps and cogeneration systems. The spark plug comprises: (a) metal shell; (b) a center electrode retained within the metal shell to be insulated from the metal shell; (c) a ground electrode joined to the metal plug, the ground electrode having a center electrode-facing surface opposed to a tip of the center electrode through a spark plug gap; and (d) an Ir-alloy chip working to produce a spark between itself and the tip of the center electrode, the Ir-alloy chip being embedded in the center electrode-facing surface of the ground electrode with a portion thereof exposed outside the center electrode-facing surface of the ground electrode.
In the preferred mode of the invention, the Ir-alloy chip other than the exposed portion thereof is installed inside the ground electrode.
The Ir-alloy chip may alternatively have at least one surface which lies flush with a side surface of the ground electrode continuing from a peripheral edge of the center electrode-facing surface.
The exposed portion of the Ir-alloy chip projects from the center electrode-facing surface of the ground electrode toward the center electrode.
The Ir-alloy chip is joined to the ground electrode through at least one fused portion in which materials of the Ir-alloy chip and the ground electrode are melted together. The fused portion may be formed by laser welding.
The shortest distance between the fused portion and the center electrode is more than or equal to the sum of an interval between the tip of the center electrode and the Ir-alloy chip through the spark plug gap and 0.3 mm.
The ground electrode has a recess formed in the center electrode-facing surface. The Ir-alloy chip is fitted within the recess. The fused portion extends continuously from an outer side wall of the ground electrode inside the Ir-alloy chip through an outer side wall of the Ir-alloy chip.
The ground electrode has a second surface opposed to the center electrode-facing surface. The tip of the fused portion lies within the Ir-alloy chip closer to the center electrode-facing surface than the second surface. The distance between the tip of the fused portion and the bottom of the Ir-alloy chip lying inside the ground electrode is greater than or equal to 0.1 mm.
The length of a part of the fused portion lying within the Ir-alloy chip is greater than or equal to 0.2 mm.
The distance between the tip of the fused portion and the center electrode-facing surface of the ground electrode is greater than or equal to 0.2 mm.
The distance between the outer side wall of the Ir-alloy chip and the outer side wall of the ground electrode is greater than or equal to 0.25 mm.
The fused portion may lie close to a joint of the ground electrode and the metal shell from a center line of the Ir-alloy chip extending toward the center electrode through the spark plug gap.
The distance between an end of the exposed portion of the Ir-alloy chip oriented toward the center electrode and the center electrode-facing surface of the ground electrode lies within a range of 0.1 mm to 1.0 mm.
The Ir-alloy chip is made from material containing a main component of Ir (Iridium) and an additive of at least one of Rh (rhodium), Pt (platinum), Ru (ruthenium), Pd (palladium), and W (tungsten). The Ir-alloy chip may contain 70 to 99 Wt % of Ir.
The Ir-alloy chip may be joined to the ground electrode through a plurality of fused portions in which materials of the Ir-alloy chip and the ground electrode are melted together. In this case, at least one of the fused portion lies preferably close to a joint of the ground electrode and the metal shell from a center line of the Ir-alloy chip extending toward the center electrode through the spark plug gap for increasing the degree of joining of the Ir-alloy chip to the ground electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.
In the drawings:
FIG. 1
is a partially sectional view which shows a spark plug with an Ir-alloy chip according to the first embodiment of the invention;
FIG.
2
(
a
) is a partially enlarged sectional view which shows a joint structure for an Ir-alloy chip in the first embodiment of the invention;
FIG.
2
(
b
) is a sectional view taken along the line A—A in FIG.
2
(
a
);
FIG.
2
(
c
) is an illustration which shows an Ir-alloy chip as viewed from a center electrode;
FIG. 3
is a partially enlarged sectional view which shows a joint structure of a spark plug sample used in durability tests;
FIG. 4
is a graph which indicates a relation between the length L
1
(mm) of a projecting portion of an Ir-alloy chip and the temperature (° C.) of the Ir-alloy chip;
FIG. 5
is a graph which indicates a relation between the length L
1
(mm) and the worn volume (mm
3
) of an Ir-alloy chip;
FIG. 6
is a graph which indicates the relation between the shortest length L
2
in FIG.
2
(
b
) and the number of sparks flying at fused portions forming joints of an Ir-alloy chip and a ground electrode;
FIG.
7
(
a
) is a sectional view which shows a modification of the first embodiment;
FIG.
7
(
b
) is a sectional view taken along the line B—B in FIG.
7
(
a
);
FIG.
8
(
a
) is a partial view which shows another modification of the first embodiment;
FIG.
8
(
b
) is a partial illustration as viewed from a direction C in FIG.
8
(
a
);
FIG.
9
(
a
) is a partially sectional view which shows a spark plug according to the second embodiment of the invention;
FIG.
9
(
b
) is a partially sectional view taken along the line D—D in FIG.
9
(
a
);
FIG. 10
is a partially plan view which shows an Ir-alloy chip and a ground electrode of a spark plug according to the third embodiment of the invention;
FIG. 11
is a partially plan view which shows an Ir-alloy chip and a ground electrode of a spark plug according to the fourth embodiment of the invention;
FIG. 12
is a partially plan view which shows an Ir-alloy chip and a ground electrode of a spark plug according to the fifth embodiment of the invention;
FIG.
13
(
a
) is a partially plan view which shows an Ir-alloy chip and a ground electrode of a spark plug according to the sixth embodiment of the invention;
FIG.
13
(
b
) is a sectional view taken along the line E—E in FIG.
13
(
a
);
FIG. 14
is a partially vertical sectional view which shows an Ir-alloy chip and a ground electrode of a spark plug according to the seventh embodiment of the invention;
FIG. 15
is a partially vertical sectional view which shows an Ir-alloy chip and a ground electrode of a spark plug according to the eighth embodiment of the invention;
FIG. 16
is a partially vertical sectional view which shows an Ir-alloy chip and a ground electrode of a spark plug according to the ninth embodiment of the invention;
FIG. 17
is a partially vertical sectional view which shows an Ir-alloy chip and a ground electrode of a spark plug according to the tenth embodiment of the invention;
FIG.
18
(
a
) is a partially horizontal sectional view which shows an Ir-alloy chip and a ground electrode of a spark plug according to the eleventh embodiment of the invention;
FIG.
18
(
b
) is a sectional view taken along the line F-Fin FIG.
18
(
a
);
FIG.
18
(
c
) is a sectional view taken along the line H—H in FIG.
18
(
a
); and
FIG. 19
is a partially vertical view which shows an Ir-alloy chip and a ground electrode of a spark plug according to the twelfth embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, wherein like reference numbers refer to like parts in several views, particularly to
FIG. 1
, there is shown a spark plug
100
which may be used in a gas engine of a generator in a cogeneration system.
The spark plug
100
includes a cylindrical metal shell
10
, a porcelain insulator
20
, a center electrode
30
, and a ground electrode
40
. The metal shell
10
has cut therein a thread
11
for mounting the spark plug
100
in an engine block (not shown). The porcelain insulator
20
made of an alumina ceramic (Al
2
O
3
) is retained within the metal shell
10
and has a tip
21
exposed outside an end
12
of the metal shell
10
.
The center electrode
30
is secured in a central chamber
22
of the porcelain insulator
20
and insulated electrically from the metal shell
10
. The center electrode
30
has a tip
31
projecting from the tip
21
of the porcelain insulator
20
outside the end
12
of the metal shell
10
. The center electrode
30
, as shown in FIG.
2
(
a
), consists of a body
32
and an Ir-alloy chip
31
a
. The body
32
is made of a cylindrical member which consists of a core portion made of a metallic material such as Cu having a higher thermal conductivity and an external portion made of a metallic material such as an Ni-based alloy having higher thermal and corrosion resistances. The Ir-alloy chip
31
a
is welded to an end of the body
32
to define the tip
31
.
The ground electrode
40
made of an Ni-alloy bar or an Fe-alloy bar is welded to the end
12
of the metal shell
10
through an intermediate block
40
a
. The intermediate block
40
a
, is made of an Ni-alloy or an Fe-alloy. The ground electrode
40
, as clearly shown in FIG.
2
(
a
), has an end
41
which faces at a side surface
42
thereof the tip
31
of the center electrode
30
through a spark plug gap
50
. The side surface
42
forms a spark discharging surface. A second Ir-alloy chip
43
is embedded in the spark discharging surface
42
which works to produce a sequence of sparks between itself and the tip
31
of the center electrode
30
.
The second Ir-alloy chip
43
, as can be seen from FIG.
2
(
a
), projects partially from the spark discharging surface
42
of the ground electrode
40
. A peripheral wall of the Ir-alloy chip
43
may either coincide partially with or be all located inside an edge of the spark discharging surface
42
. In this embodiment, the whole of the Ir-alloy chip
43
is, as shown in FIG.
2
(
c
), located inside the periphery of the spark discharging surface
42
.
The attachment of the Ir-alloy chip
43
to the ground electrode
40
is accomplished in the following manner. First, the Ir-alloy chip
43
is put on the spark discharging surface
42
and forced thereinto to form a recess
44
which has substantially the same area as that of the Ir-alloy chip
43
. The laser beams are, as shown in FIG.
2
(
b
), applied to each outer side wall of the recess
44
to form fused portions
45
where materials of the ground electrode
40
and the Ir-alloy chip
43
are melted together, thereby producing joints of the Ir-alloy chip
43
and the ground electrode
40
. The recess
44
may alternatively be formed using cutting or cold forging techniques.
The Ir-alloy chip
43
, as can be seen from FIG.
2
(
a
), projects partially from the spark discharging surface
42
toward the tip
31
of the center electrode
30
to define the spark plug gap
50
, as described above.
Each of the Ir-alloy chips
31
a
and
43
is made from material containing a main component of Ir (Iridium) and an additive of at least one of Rh (rhodium), Pt (platinum), Ru (ruthenium), Pd (palladium), and W (tungsten). In this embodiment, the Ir-alloy chips
31
a
and
43
each contain 90 Wt % of Ir and 10 Wt % of Rh (referred to as an Ir-10 Rh below).
The Ir-alloy chip
43
is, as discussed above, located inside the outer periphery of the spark discharging surface
42
. Specifically, most of the Ir-alloy chip
43
is surrounded by the ground electrode
40
in contact therewith. Therefore, when a spark discharge is taken place between the Ir-alloy chips
43
and
31
a
, the heat produced in the Ir-alloy chip
43
flows to the metal shell
10
through the ground electrode
40
effectively, thus resulting in an increased degree of dissipation of heat from the Ir-alloy chip
43
as compared with the conventional spark plug as discussed in the introductory part of this application.
We researched a suitable length L
1
, as shown in
FIG. 3
, of a portion of the Ir-alloy chip
43
projecting from the end
41
of the ground electrode
40
in terms of the degrees of dissipation of heat from the Ir-alloy chip
43
and spark-caused wear of the Ir-alloy chip
43
. We first performed durability tests of the spark plug
100
for different lengths L
1
of 4 mm to −2 mm. The spark plug
100
was installed in a 6-cylinder gas cogeneration engine and run for 500 hours under a condition of a rated engine output. A thermocouple thermometer was used to measure the temperature of the Ir-alloy chip
43
. After the durability tests, a worn volume of the Ir-alloy chip
43
was measured.
FIG. 4
indicates a relation between the length L
1
(mm) of the projecting portion of the Ir-alloy chip
43
and the temperature (° C.) of the Ir-alloy chip
43
.
FIG. 5
indicates a relation between the length L
1
(mm) and the worn volume (mm
3
) of the Ir-alloy chip
43
. The graph of
FIG. 4
shows that the temperature of the Ir-alloy chip
43
is lowered most when the length L
1
is less than 0 mm. Similarly, the graph of
FIG. 5
shows that the worn volume of the Ir-alloy chip
43
is minimized when the length L
1
is less than 0 mm. This is because when the length L
1
is decreased below 0 mm, the oxidation-caused wear of the Ir-alloy chip
43
is suppressed to increase the spark wear resistance thereof. Note that length L
1
m=0 mm indicates the case where the end of the Ir-alloy chip
43
lies flush with the outer periphery of the spark discharging surface
42
.
As apparent from the above discussion, most of the Ir-alloy chip
43
is embedded in the spark discharging surface
42
, thus resulting in an increased degree of heat dissipation from the Ir-alloy chip
43
. The Ir-alloy chip
43
has one surface exposed outside the spark discharging surface
42
toward the tip
31
of the center electrode
30
, thereby enabling the spark plug gap
50
to be defined allowing for the amount of spark-caused wear of the Ir-alloy chip
43
, which results in an increase in service left of the spark plug
100
. A sequence of sparks are produced mainly between the tip
31
of the center electrode
30
and the Ir-alloy chip
43
, thus minimizing the amount of wear of the spark discharging surface
42
of the ground the spark plug
100
.
The Ir-alloy chip
43
is, as described above, laser-welded to the ground electrode
40
to form the fused portions
45
. If the shortest distance, as shown in FIG.
2
(
a
), between the tip
31
of the center electrode
30
and each of the fused portions
45
is defined as L
2
, it is advisable that L
2
be longer than the sum of the distance G between the Ir-alloy chips
31
and
43
through the spark plug gap
50
and 0.3 mm. This value is found based on results of tests, as discussed below, performed by the inventors of this application in terms of the relation between the shortest distance L
2
and sparks landing on the fused portions
45
.
In the tests, spark plugs with the Ir-alloy chip
43
whose gap
50
(i.e., the distance G) lies within a range of 0.3 mm to 0.8 mm and which have different length L
2
were prepared. The spark plugs were installed in a test chamber under a gauge pressure of 0.6 Mpa. The voltage was applied to each of the spark plugs to produce a sequence of sparks to measure the number of sparks flying at the fused portions
45
.
FIG. 6
indicates the relation between the shortest length L
2
and the number of sparks flying at the fused portions
45
and shows that all the sparks fly within the spark plug gap
50
when the distance G is 0.3 mm, as indicated by black circles, and the shortest length L
2
is more than 0.5 mm or more, when the distance G is 0.5 mm, as indicated by black triangles, and the shortest length L
2
is 0.8 mm or more, and when the distance G is 0.8 mm, as indicated by black squares, and the shortest length L
2
is more than 1.15 mm or more. Specifically, when length L
2
≧G+0.3 mm, the possibility that sparks occur between the fused portions
45
and the tip
31
of the center electrode
30
will be zero (0), thus minimizing the spark-caused wear of the fused portions
45
.
The Ir-alloy chip
43
is welded to the inner wall of the recess
44
in the ground electrode
40
by irradiating laser beams to the outer wall of the recess
44
, so that the fused portions
45
which contain less Ir than the Ir-alloy chip
43
and are inferior in spark wear resistance are formed outside a spark discharging portion of the ground electrode
40
, thereby minimizing the spark-caused wear of the fused portions
45
.
The surface of the Ir-alloy chip
43
exposed to the spark plug gap
50
is, as shown in FIG.
2
(
c
), rectangular, however, may alternatively be, as shown in FIG.
7
(
a
), circular. Specifically, the Ir-alloy chip
43
may be made of an Ir-alloy disc. FIG.
7
(
b
) shows a vertical cross section taken along the line B—B in FIG.
7
(
a
).
The Ir-alloy chip
43
may alternatively be embedded in the ground electrode
40
in the manner as illustrated in FIGS.
8
(
a
) and
8
(
b
). FIG.
8
(
b
) shows the surface of the Ir-alloy chip
43
as viewed from a direction C in FIG.
8
(
a
). Specifically, the ground electrode
40
has a C-shaped opening
60
formed in the end thereof by cutting or forging. The Ir-alloy chip
43
is fitted in and laser-welded to the C-shaped chamber
60
in the same manner as described above. The laser beams may alternatively be irradiated to an interface between an inner wall of the opening
60
and an outer wall of the Ir-alloy chip
43
to weld the Ir-alloy chip
43
to the ground electrode
40
. The ground electrode
40
may be installed, as shown in FIG.
8
(
a
), directly on the end of the metal shell
10
.
FIGS.
9
(
a
) and
9
(
b
) show the second embodiment of the invention.
Usually, the thermal stress arising from burning of the engine may cause cracks to be formed between the Ir-alloy chip
43
and the fused portions
45
which lead to dislodgement of the Ir-alloy chip
43
from the ground electrode
40
. Particularly, when used in a gas cogeneration engine operated continuously under high loads, spark plugs are exposed at electrodes to intense heat, thus having a high possibility of formation of such cracks.
The second embodiment aims at forming the fused portions
45
under optimum conditions in order to avoid the dislodgement of the Ir-alloy
43
from the ground electrode
40
. FIG.
9
(
a
) illustrates the Ir-alloy chip
43
embedded in the ground electrode
40
, as viewed from the side of the center electrode
30
. FIG.
9
(
b
) is a sectional view taken along the line D—D in FIG.
9
(
a
).
The Ir-alloy chip
43
is made of a disc member. The Ir-alloy chip
43
is fitted in the recess
44
of the ground electrode
40
and laser-welded to form, as clearly shown in FIG.
9
(
a
), five fused portions
45
. The fused portions
45
each extend continuously from the outer side surface
46
of the ground electrode
40
to a central portion of the Ir-alloy chip
43
through an outer side wall
47
of the Ir-alloy chip
43
. The Ir-alloy chip
43
is, like the first embodiment, exposed partially outside the surface of the ground electrode
40
toward the center electrode
30
through the spark plug gap
50
. The ground electrode
40
is joined at the right side thereof, as viewed in the drawings, to the metal shell
10
.
We made a study of optimum conditions for forming the fused portions
45
, which will be discussed below in detail.
The tip of each of the fused portions
45
is, as can be seen from FIG.
9
(
b
), located closer to the spark discharging surface
42
of the ground electrode
40
than the bottom
48
of the Ir-alloy chip
43
. Durability tests were performed for different values of distance L
3
between the bottom
48
of the Ir-alloy chip
43
and the tip of each of the fused portions
45
using spark plug samples prepared in three sets of four. The three sets have L
3
=0 mm, L
3
=0.1 mm, L
3
=0.2 mm, respectively. In each sample, the length L
4
of a tip of each of the fused portions
45
entering the Ir-alloy chip
43
was 0.5 mm.
The spark plug samples were exposed to air at 1000° C. for six minutes, after which they were left in air at 25° C. for six minutes. This thermal shock test were repeated cyclically (i.e., a thermal cycle test). The spark plug samples having L
3
=0 mm all experienced dislodgement of the Ir-alloy chip
43
from the ground electrode
40
before 100 cycles of the thermal shock tests. The spark plug samples having L
3
=0.1 mm and L
3
=0.2 mm all did not experience dislodgement of the Ir-alloy chip
43
from the ground electrode
40
even after 800 cycles of the thermal shock tests. It is, therefore, found that the distance L
3
between the tip of the fused portions
45
and the bottom
48
of the Ir-alloy chip
43
is preferably greater than or equal to 0.1 mm (i.e., L
3
≧0.1 mm) in order to avoid the dislodgement of the Ir-alloy chip
43
from the ground electrode
40
.
Each of the fused portions
45
, as can be seen from FIG.
9
(
b
), extends perpendicular to a direction in which the Ir-alloy chip
43
peels off the ground electrode
40
. Thus, when the distance L
3
is set more than 0.1 m, a relatively thick bottom wall
70
is defined beneath the fused portions
45
, thereby keeping tight engagement of the Ir-alloy chip
43
with the inner wall of the recess
44
even if cracks occur between the Ir-alloy chip
43
and the fused portions
45
.
Additionally, similar thermal shock tests were also performed for different values of length L
4
of the tip of each of the fused portions
45
entering the Ir-alloy chip
43
using spark plug samples prepared in three sets of four. The three sets have L
4
=0.2 mm, L
4
=0.5 mm, L
4
=0.8 mm, respectively. In each sample, the distance L
3
between the tip of each of the fused portions
45
and the bottom
48
of the Ir-alloy chip
43
was 0.2. All the spark plug samples do not experience the dislodgement of the Ir-alloy chip
43
from the ground electrode
40
even after 800 cycles of the thermal shock tests. It is, thus, found that when the distance L
3
is more than or equal to 0.1, and the length L
4
is more than or equal to 0.2, it enhances the avoidance of dislodgement of the Ir-alloy chip
43
from the ground electrode
40
.
We also made a study of suitable values of distance L
5
between the tip of each of the fused portions
45
and the spark discharging surface
42
of the ground electrode
40
and found that the distance L
5
of more than or equal to 0.2 is required for forming the fused portions
45
desirably.
The above thermal shock tests also showed that when the distance L
6
between the outer side wall
47
of the Ir-alloy chip
43
(i.e., a line tangent to the outer side wall
47
of the Ir-alloy chip
43
) and the outer side wall
46
of the ground electrode
40
is less than 0.25 mm, it may cause cracks to be formed in the ground electrode
40
before dislodgement of the Ir-alloy chip
43
. It is, thus, advisable that distance L
6
be more than or equal to 0.25 mm.
We further made a study of suitable values of length L
7
of a portion of the Ir-alloy chip
43
exposed outside the spark discharging surface
42
toward the center electrode
30
and found that when the length L
7
is set more than or equal to 0.1, it enables a sequence of sparks to be produced between the center electrode
30
and the Ir-alloy chip
43
and also serves to prevent sparks from flying directly at the ground electrode
40
, and that when the length L
7
is more than 1.0 mm, the temperature of the Ir-alloy chip
43
is elevated undesirably by the heat of burning of the engine, which will result in an increase in wear of the Ir-alloy chip
43
. Therefore, it is advisable that the length L
7
meet a relation of 0.1≦L
7
≦1.0 mm.
In order to enhance the heat flow from the Ir-alloy chip
43
, at least one of the fused portions
45
is preferably formed close to the joint of the ground electrode
40
and the metal shell
10
(i.e., the right side of the drawings) from a vertical center line
80
of the Ir-alloy chip
43
. In this embodiment, two of the fused portions
45
are located on the right side of the vertical center line
80
.
The shortest distances L
6
between the outer side wall
46
of the ground electrode
40
and the outer side wall
47
of the Ir-alloy chip
43
are preferably equal to each other because it makes it possible to form the fused portions
45
in the same welding condition, thereby facilitating ease of a welding operation or resulting in a decrease in manufacturing process.
FIG. 10
shows the Ir-alloy chip
43
embedded in the ground electrode
40
according to the third embodiment of the invention, as viewed from the side of the center electrode
30
.
Two corners of the tip of the ground electrode
40
are cut to form surfaces
85
tapering off to the tip. The fused portion
45
is formed in each of the tapered surfaces
85
. It is advisable that the distances L
6
be equal to each other for facilitating ease of the welding operation to join the Ir-alloy chip
43
to the ground electrode
40
. Other arrangements are identical with those in the first embodiment, and explanation thereof in detail will be omitted here.
FIG. 11
shows the fourth embodiment of the invention which is different from the one shown in
FIG. 10
in that two tapered surfaces
86
are formed on the tip of the ground electrode
40
which traverse each other to define a sharp tip and which have the fused portions
45
formed therein. It is advisable that the distances L
6
between the outer side wall of the Ir-alloy chip
43
and portions of the outer side wall of the ground electrode
40
in which the fused portions
45
are to be formed be equal to each other for facilitating ease of the welding operation to join the Ir-alloy chip
43
to the ground electrode
40
. Other arrangements are identical with those in the third embodiment, and explanation thereof in detail will be omitted here.
FIG. 12
shows the fifth embodiment of the invention which is different from the ones shown in
FIGS. 10 and 11
in that the ground electrode
40
has a round tip in which the fused portions
45
are formed at constant angular intervals. It is advisable that the distance L
6
between the outer side wall of the Ir-alloy chip
43
and the outer side wall of the round tip of the ground electrode
40
be constant for facilitating ease of the welding operation to join the Ir-alloy chip
43
to the ground electrode
40
. Other arrangements are identical with those in the third and fourth embodiments, and explanation thereof in detail will be omitted here.
FIGS.
13
(
a
) and
13
(
b
) show the sixth embodiment of the invention which is a modification of the one shown in FIG.
10
.
Seven fused portions
45
are formed in the outer side wall of the ground electrode
40
, while two fused portions
45
are also formed in the bottom
49
of the ground electrode
40
(i.e., the surface of the ground electrode
40
opposite the center electrode
30
) and extend inside the Ir-alloy chip
43
.
FIG. 14
shows the seventh embodiment of the invention which is different from the above embodiments only in that a single fused portion
45
is formed in the outer side wall
46
of the ground electrode
40
to define a wider bottom wall
70
which establishes tight engagement with the inner wall of the recess
44
. This structure also provides substantially the same effects as those in the above embodiments.
FIG. 15
shows the eighth embodiment of the invention.
The joining of the Ir-alloy chip
43
to the ground electrode
4
is achieved by at least one fused portion
45
extending from the outer side wall
46
of the ground electrode
40
inside the Ir-alloy chip
43
and a plurality of fused portions
45
extending downward, as viewed in the drawing, from the surface of the ground electrode
40
exposed outside the spark discharging surface
42
of the ground electrode
40
. The vertical fused portions
45
extend through the outer side wall
47
of the Ir-alloy chip
43
, that is, they extend through an interface between the outer side wall
47
of the Ir-alloy chip
43
and the inner wall of the recess
44
.
FIG. 16
shows the ninth embodiment of the invention.
A plurality of fused portions
45
are formed in a corner defined between the outer side wall of the Ir-alloy chip
47
and the spark discharging surface
42
. Specifically, the fused portions
45
extend from the outer side wall
47
of the Ir-alloy chip
43
and the spark discharging surface
42
of the ground electrode
40
diagonally toward the vertical center line
80
of the Ir-alloy chip
43
so as to define the bottom wall
70
of a given thickness beneath the fused portions
45
which establishes tight engagement with the inner wall of the recess
44
.
FIG. 17
shows the tenth embodiment of the invention.
The Ir-alloy chip
43
is made of a cylindrical member consisting of a small-diameter portion
92
and a large-diameter portion
95
. The small-diameter portion
92
is fitted within the recess
44
of the ground electrode
40
, while the large-diameter portion is placed on the spark discharging surface
42
of the ground electrode
40
. The fused portions
45
are formed around the outer side wall
47
of the small-diameter portion
92
. This structure provides a relatively wider spark-discharging surface to the Ir-alloy chip
43
without sacrificing the distances L
6
between the outer side wall
47
of the small-diameter portion
92
of the Ir-alloy chip
43
and portions of the outer side wall
46
of the ground electrode
40
in which the fused portions
45
are to be formed.
FIGS.
18
(
a
),
18
(
b
), and
18
(
c
) show the eleventh embodiment of the invention. FIG.
18
(
a
) is a sectional view which illustrates the Ir-alloy chip
43
embedded in the ground electrode
40
as viewed from the center electrode
30
. FIG.
18
(
b
) is a sectional view taken along the line F-Fin FIG.
18
(
a
). FIG.
18
(
c
) is a sectional view taken along the line H—H in FIG.
18
(
a
).
The Ir-alloy chip
43
is made of a square block (i.e., a prism) and has a side surface exposed, as clearly shown in FIG.
18
(
c
), outside the end
46
of the ground electrode
40
. Three fused portions
45
are formed in each side wall of the ground electrode
40
. Other arrangements are identical with those in the above embodiments, and explanation thereof in detail will be omitted here.
FIG. 19
shows the twelfth embodiment of the invention.
The ground electrode
40
has a chamber
44
formed in an end portion thereof which opens into the spark discharging surface
42
and the bottom
49
. The Ir-alloy chip
43
is fitted within the opening
44
. This structure provides for ease of machining of the chamber
44
.
While the present invention has been disclosed in terms of the preferred embodiments in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in the appended claims. For example, the joining of Ir-alloy chip
43
to the ground electrode
40
may be achieved with resistance welding or plasma arc welding. The invention may also be used with a spark plugs of the type, as taught in U.S. Pat. No. 6,225,752, in which a sequence of sparks are produced between a side peripheral wall of a center electrode and an end of a ground electrode. In this case, the Ir-alloy chip
43
is installed in the end of the ground electrode. The Ir-alloy chips
31
a
and
43
are each made from material containing 90 Wt % of Ir, but may be made from material containing 70 to 99 Wt % of Ir.
Claims
- 1. A spark plug comprising:a metal shell; a center electrode retained within said metal shell to be insulated from said metal shell; a ground electrode joined to said metal shell, said ground electrode having a center electrode-facing surface opposed to a tip of said center electrode through a spark plug gap, said ground electrode having a recess formed in the center electrode-facing surface; and an Ir-alloy chip working to produce a spark between itself and the tip of said center electrode, said Ir-alloy chip being embedded in the center electrode-facing surface of said ground electrode with a portion thereof exposed outside the center electrode-facing surface of said ground electrode, wherein said Ir-alloy chip other than the exposed portion thereof is installed inside said ground electrode, and said Ir-alloy chip is joined to said ground electrode through at least one fuse portion in which materials of said Ir-alloy chip and said ground electrode are melted together, said Ir-alloy chip being fitted within said recess, said fused portion extending continuously from an outer side wall of said ground electrode inside said Ir-alloy chip through an outer side wall of said Ir-alloy chip, the outer side wall of the ground electrode being defined between the center electrode-facing surface of the ground electrode and a surface of the ground electrode opposite the center electrode-facing surface.
- 2. A spark plug as set forth in claim 1, wherein said Ir-alloy chip has at least one surface which lies flush with a side surface of said ground electrode continuing from a peripheral edge of the center electrode-facing surface.
- 3. A spark plug as set forth in claim 1, wherein the exposed portion of said Ir-alloy chip projects from the center electrode-facing surface of said ground electrode toward said center electrode.
- 4. A spark plug as set forth in claim 3, wherein a distance between an end of the exposed portion of said Ir-alloy chip oriented toward said center electrode and the center electrode-facing surface of said ground electrode lies within a range of 0.1 mm to 1.0 mm.
- 5. A spark plug as set forth in claim 1, wherein the fused portion is formed by laser welding.
- 6. A spark plug as set forth in claim 1, wherein the shortest distance between the fused portion and said center electrode is more than or equal to the sum of an interval between the tip of said center electrode and said Ir-alloy chip through an outer side wall of said Ir-alloy chip.
- 7. A spark plug as set forth in claim 1, wherein said ground electrode has a second surface opposed to the center electrode-facing surface, a tip of the fused portion lies within said Ir-alloy chip closer to the center electrode-facing surface than the second surface, and a distance between a tip of the fused portion and a bottom of said Ir-alloy chip lying inside said ground electrode is greater than or equal to 0.1 mm.
- 8. A spark plug as set forth in claim 1, wherein a length of a part of the fused portion lying within said Ir-alloy chip is greater than or equal to 0.2 mm.
- 9. A spark plug as set forth in claim 1, wherein a distance between a tip of the fused portion and the center electrode-facing surface of said ground electrode is greater than or equal to 0.2 mm.
- 10. A spark plug as set forth in claim 1, wherein a distance between the outer side wall of said Ir-alloy chip and the outer side wall of said ground electrode is greater than or equal to 0.25 mm.
- 11. A spark plug as set forth in claim 1, wherein the fused portion lies close to a joint of said ground electrode and said metal shell from a center line of said Ir-alloy chip extending toward said center electrode through the spark plug gap.
- 12. A spark plug as set forth in claim 1, wherein said Ir-alloy chip is made from material containing a main component of Ir (Iridium) and an additive of at least one of Rh (rhodium), Pt (platinum), Ru (ruthenium), Pd (palladium), and W (tungsten).
- 13. A spark plug as set forth in claim 12, wherein said Ir-alloy chip contains 70 to 99 Wt % of Ir.
- 14. A spark plug as set forth in claim 1, wherein said Ir-alloy chip is joined to said ground electrode through a plurality of fused portions in which materials of said Ir-alloy chip and said ground electrode are melted together, and wherein at least one of the fused portion lies close to a joint of said ground electrode and said metal shell from a center line of said Ir-alloy chip extending toward said center electrode through the spark plug gap.
Priority Claims (2)
Number |
Date |
Country |
Kind |
2000-208824 |
Jul 2000 |
JP |
|
2001-163155 |
May 2001 |
JP |
|
US Referenced Citations (11)
Foreign Referenced Citations (2)
Number |
Date |
Country |
8298178 |
Nov 1996 |
JP |
2000-40577 |
Aug 2000 |
JP |