U.S. patent number 3,868,530 [Application Number 05/376,524] was granted by the patent office on 1975-02-25 for spark plug.
This patent grant is currently assigned to Champion Spark Plug Company. Invention is credited to Carl J. Eaton, Richard S. Podiak.
United States Patent |
3,868,530 |
Eaton , et al. |
February 25, 1975 |
SPARK PLUG
Abstract
This invention relates to spark plugs for internal combustion
engines and is particularly directed to a center electrode having a
sparking tip composed of a precious metal and to the method of
making the same. The known advantage of the use of a precious metal
electrode is that considerably greater spark plug life is achieved.
The invention achieves the advantage while greatly reducing the
mass of precious metal employed. A further feature of the invention
is the co-planar disposition of the end of the center electrode and
its supporting insulator.
Inventors: |
Eaton; Carl J. (Toledo, OH),
Podiak; Richard S. (Maumee, OH) |
Assignee: |
Champion Spark Plug Company
(Toledo, OH)
|
Family
ID: |
23485359 |
Appl.
No.: |
05/376,524 |
Filed: |
July 5, 1973 |
Current U.S.
Class: |
313/141; 445/7;
313/144; 445/29 |
Current CPC
Class: |
H01T
13/39 (20130101) |
Current International
Class: |
H01T
13/39 (20060101); H01t 013/20 () |
Field of
Search: |
;313/141R,141.1,144,145,136,118 ;29/25.12 ;123/169EL |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brody; Alfred L.
Attorney, Agent or Firm: Owen & Owen
Claims
What we claim is:
1. In a spark plug having a grounded shell, an insulator, at least
one ground electrode carried by the shell, and a center electrode
extending through said insulator and terminating in sparking
relationship with said ground electrode, said center electrode
being formed of metal having good spark corrosion resistant
properties, the improvement comprising an axial recess in the
firing end of the center electrode, said recess being larger in
cross section at its inner end than at its outer end, and an insert
of precious metal extending into and filling the recess, said
insert being firmly supported by the adjacent electrode with its
end exposed at the firing end of the electrode.
2. The improvement defined in claim 1 wherein the insert is a
corrosion resistant metal alloy selected from the group consisting
of gold, platinum, palladium, ruthenium, rhenium, rhodium and
tungsten.
3. The improvement defined in claim 1 wherein the axial recess is
frustoconical in shape.
4. The improvement defined in claim 1 wherein a portion of said
precious metal insert extends outside the recess in the center
electrode.
Description
BACKGROUND OF THE INVENTION
It is known in the art to use precious or semi-precious metals as
electrode tips in spark plugs for prolonged life. For example, in
the U.S. Pat. No. 2,296,033 to Heller the precious metal tip is
welded to a body of much less expensive metal forming the center
electrode and itself acts as the firing tip. This is true in a
number of earlier designs. It has also been proposed to use
tungsten or a tungsten alloy in such a construction as, for
example, in the U.S. Pat. No. 2,391,455 to Hensel. However,
tungsten and tungsten alloys corrode rapidly in some modern
internal combustion engines and any construction in which the sides
of the tungsten tip are not protected show very low electrode life
in certain services.
It is also known in the art, by the U.S. Pat. No. 2,391,456 to
Heller, that the end of an electrode may be capped with a sheath of
platinum or the like to form a long-wearing electrode where the
core of the electrode is composed of molybdenum or a molybdenum
alloy having high heat conductivity and a coefficient of thermal
expansion substantially the same as that of the cap or sheath. The
most common constructions have been to use a rivet of platinum
seated in the bore of the insulator tip or into the bore of a split
nickel sleeve as in the U.S. Pat. No. 3,256,457 to Bretsch. The
rivet is held in place by casting silver metal around the upper
portion of the rivet head.
In practice the rivet construction requires a large amount of
precious metal which contributes nothing useful to the sparking
life of the electrode. A very large portion of the precious metal
is wasted as a support rod. Also in practice it has been found
difficult to attach the rivet securely for long periods of
operation in the corrosive atmosphere of the combustion
chamber.
In all of the prior art constructions the quantity of precious
metal used is so high that, under modern conditions the price of
the spark plug becomes excessive and the limited resources of the
precious metals are largely wasted.
In known spark plugs, the center electrode protrudes from its
supporting insulator and deposits on the insulator surface are
deliberately excluded from the firing process. It has been found
that under some circumstances these deposits can actually be used
in a beneficial manner to extend the life of the spark plug.
BRIEF DESCRIPTION OF THE INVENTION
The preferred form of the invention is an electrode comprising a
base metal tube or drilled rod, such as a nickel alloy tube or a
bored nickel alloy rod into the bore of which is inserted a short
section of fine wire of a precious metal such as platinum or a
platinum alloy. However, in place of platinum various other
precious or semi-precious metals may be used including tungsten
which is much less expensive. In this construction, the fine wire
section utilized can be as low as 10 percent of that required by
current known constructions to achieve comparable electrode
life.
The fine section of precious metal wire having been inserted in the
bore of the nickel tube, the tube is then swaged to reduce its
diameter somewhat and to effectively lock the fine wire in place
mechanically. The assembled electrode is then put into a supporting
insulator and in the preferred form of the invention, positioned
with the sparking surface flush with the insulator tip. However,
the electrode may project beyond the insulator tip if desired.
In a second execution of the invention, the nickel electrode is
outwardly flared and an end cavity is drilled or pierced to receive
a small cylindrical section of precious metal wire. The nickel is
then swaged back into its original diameter. This action firmly
locks the precious metal insert into the base metal electrode by
causing an undercut diameter in the precious metal wire at the
position of entrance into the end of the base metal electrode. The
swaging forces the trapped portion of the precious metal into full
and firm engaging relationship with the electrode metal. This
method of execution is effective for all precious and semi-precious
metal insert alloys having ductility and malleability
characteristics better than or equal to the base metal
electrode.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is an elevational view with a portion shown as a central,
vertical section of a spark plug having a center electrode formed
according to the present invention.
FIGS. 2 and 3 are fragmentary sectional views of the center
electrode itself, somewhat enlarged to indicate the method of
manufacture.
FIG. 4 is a central sectional view of an electrode showing a
typical condition after operation for an extended period and in
which the precious metal wire has become exposed by reason of
erosion of the nickel sheath.
FIGS. 5 and 6 are fragmentary central sectional views showing a
modification of the invention in which a small cylindrical pellet
of precious metal is used; and
FIG. 7 is a fragmentary view, with parts in section, of a spark
plug having a modified electrode form corresponding to FIG. 6.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 of the drawings shows a substantially conventional spark
plug having a shell 10 that is adapted to be received in the
threaded opening in an engine cylinder head. The plug comprises an
insulator 11 seated in the shell 10, the insulator having a bore
which receives a center electrode 15. The center electrode is
positioned in a bore 16 of the insulator 11 and sealed against gas
leakage by a tamped mass of powder 17 or by any other suitable
means. The center electrode 15 includes a lower section 18 which
may be made tubular or which may be drilled out to provide a
central longitudinal hole for the purpose hereinafter described. A
ground electrode 19 completes the spark plug. It will be noted that
in the form of the invention shown in FIG. 1, the end of the lower
section or firing end of the center electrode 18 is co-planar or
flush with the flat end of the insulator 11.
As indicated in FIG. 2 the lower electrode section 18, having been
made tubular or having been drilled out, receives a fine wire
insert which is, in the form shown made in two sections. One
section of the fine wire insert is made from a precious metal and
is designated 21. The remaining section of the wire insert is
designated 22 and is made of a base metal such as iron or nickel
merely to fill the bore of the nickel tube 18. In the preferred
form the fine wire insert may range in diameter between 0.010 inch
to approximately 0.030 inch and its length is between 0.150 inch
and 0.250 inch. Above the larger diameter the construction ceases
to show all of the economies desired. Below the finer diameter the
small section of precious metal wire becomes very difficult to
handle in assembling the electrode and the finer wires are
therefore not preferred. Alloys of gold, platinum, palladium,
rhodium, rhenium, ruthenium and tungsten are among the so-called
precious metals that may be used for the exposed section of the
fine wire electrode. Substantially the only criterion is that the
precious metal alloy be such that it can be drawn into wire form
and that it will resist sparking erosion.
After the fine wire section of precious metal 21 and the fine wire
base metal section 22 are inserted into the bore of the nickel
tube, which thereafter acts as a sheath for the fine wire insert,
the assemblage is swaged to reduce the diameter of the lower
electrode section somewhat and to lock the sections 21 and 22 in
place in the sheath by mechanical adherence between the wire and
the nickel sheath. It has been found that the swaged electrode
stays together through repeated heating and cooling cycles because
of the long axial contact between the insert and the nickel sheath.
The apparatus used to accomplish the swaging step is
conventional.
Sparking between the ground electrode 19 and the center electrode
18 takes place initially across the entire surface of the center
electrode, since the sparking will occur to the point of least
sparking voltage requirement. The nickel sheath, being somewhat
less resistant to erosion, wears away leaving a small protruding
tip of the precious metal wire exposed as indicated in FIG. 4. This
Figure, then, diagrammatically represents the condition of the
center electrode after several thousand miles of operation of the
spark plug. It will be noted that the nickel sheath has eroded away
but that the precious metal wire is still in its original condition
and in operative relation to the ground electrode and the spark
plug will still be capable of firing at a low sparking voltage.
During operation of an engine on even lightly leaded fuels,
conductive deposits form on the end of the insulator. By making
this surface co-planar with the end of the electrode these
conductive deposits participate in the sparking process and
actually act as a center electrode to which sparks of an intensity
sufficient to fire the cylinder charge can occur. This prolongs
further the life of the spark plug of the present invention.
While experimental evidence indicates that a fine hole can be
drilled axially into a rod of nickel to form the lower center
electrode section 18, in practice the use of a nickel tube will be
much more practical.
The base metal section 22 of the fine wire insert is used only to
plug the bore of the tube 18 and conserve on the quantity of
precious metal wire. The base metal plug will also produce a
uniform outside diameter of the electrode during swaging and will
assist in plugging the tube against gas leakage.
When the insert metal used is tungsten or a tungsten alloy wire,
which is relatively inexpensive as compared to platinum or platinum
alloy, the nickel sheath serves to protect the sides of the
tungsten wire against chemical attack by the combustion gases.
Tungsten alloys are found to be highly satisfactory meterials for
electrode use if the non-sparking surfaces can be adequately
protected. The tightly swaged nickel sheath serves to protect the
tungsten insert and confines the erosion and corrosion only to the
exposed end face.
In the form of the invention shown in FIGS. 5 and 6 the precious
metal is initially in the form of a small cylindrical pellet 30.
The nickel electrode is shown at 31. The electrode is pierced at
its firing end to form a recess 32 and the adjacent metal of the
electrode is flared out as at 33. The pellet 30 is placed in the
recess 32 and the assembly is swaged to force the nickel into
intimate engagement with the side walls of the pellet as shown in
FIG. 6. The swaging action causes the enlarged portion 33 of
electrode 31 to exert greater radial pressure on the mid portion of
the precious metal pellet 30 resulting in an undercut diameter in
the pellet 30 at the point where it emerges from the nickel
electrode 31. This action traps the portion of the insert 30 which
is within the cavity 32 and forces it into full and tight contact
with the walls of the cavity.
In production it may be found that handling the very small pellets
30 is impractical, in which case the pellet 30 will be formed after
the swaging step and the process becomes one in which the end of a
long wire will be inserted in the recess 32, the assembly swaged
and the pellet then severed from the wire.
During swaging, the precious metal of the pellet can be left
extended from the nickel wire 31, if desired, as shown in FIG. 7.
With this construction the sparking will occur generally only to
the precious metal because the nickel will be too far away for
sparking and the configuration of the tip of the plug will not
change significantly after prolonged use. In this form also,
however, the protrusion of the precious metal from the nickel may
be omitted if desired.
* * * * *