Electric lamp and discharge devices – Spark plugs – Plural series gaps
Patent
1984-06-07
1987-01-27
DeMeo, Palmer C.
Electric lamp and discharge devices
Spark plugs
Plural series gaps
313125, 313128, 313130, 313143, 315 51, H01T 1346
Patent
active
046396357
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF INVENTION
The invention relates to a spark plug, particularly though not exclusively for use in an internal combustion engine.
BACKGROUND ART
In common spark plugs, combustion is initiated from a plasma generated by striking an arc between two electrodes. With typical spark energies of 30 to 40 mJ. these devices are not capable of igniting mixtures with an air/fuel ratio significantly greater than stoichiometric.
Published work indicates that a jet of plasma is much more efficient at igniting mixtures with a high air/fuel ratio (see, for example, SAE Technical Papers 770355 and 800042). In spark plugs designed to generate jets of plasma at a high air/fuel ratio, a high energy (>1 Joule) is required to be dissipated in the arc.
DISCLOSURE OF INVENTION
It is an object of the invention to seek to mitigate this disadvantage of prior plasma jet type spark plugs.
A spark plug according to the invention is characterized by at least two insulated electrodes and an earth electrode so arranged with respect to one another that arcs are struck in series between successive electrodes.
Spark plugs embodying the invention are hereinafter described, by way of example, with reference to the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is schematic longitudinal sectional view of one proposed or traditional spark plug;
FIG. 2 is a schematic longitudinal sectional view of another proposed spark plug;
FIG. 3 is a schematic longitudinal sectional view of a spark plug according to the invention;
FIG. 4 is a schematic longitudinal sectional view of a second embodiment of spark plug according to the invention;
FIGS. 5 to 8 are schematic longitudinal sectional views respectively of different electrode configurations of spark plugs according to the invention;
FIG. 9 is schematic longitudinal sectional view of a further spark plug according to the invention; and
FIG. 10 is schematic lay-out of a driver unit for a spark plug according to the invention.
Referring to the drawings, FIG. 1 shows a spark plug in which combustion is initiated from a plasma generated by striking an arc between electrodes A and B. With typical spark energies of 30 to 40 mJ. such a plug is not capable of igniting mixtures with an air/fuel ratio significantly greater than stoichiometric. FIG. 2 shows a cross section of a relevant part of another proposed spark plug which can generate a plasma jet for igniting combustible mixtures with a high air/fuel ratio. An arc is struck between end electrode A and centre insulated electrode B, within cavity C in ceramic body D. Providing sufficient energy is dissipated in the arc (>1 Joule), a high level of ionization is produced in the cavity C. The energy dissipated also heats the gas, causing it to expand rapidly. Consequently, ionized gas is ejected from the cavity C as a plasma jet E.
Spark plugs embodying the invention are illustrated in FIGS. 3-9, in which like reference symbols are used for like parts.
Referring to FIG. 3 there is shown a spark plug 1 embodying the invention, which is essentially a twin gap spark plug for producing a plasma jet at E. The relevant, spark forming part of the spark plug 1 has an insulator in the form of a ceramic body 2 terminating at a surface 3, the insulator encompassing a cavity 4 in which there is a (central) insulated electrode 5. There is also an insulated electrode 6 and an earth electrode 7. The electrodes are spaced apart and form sequential pairs 7-6 and 6-5. More particularly, as will be appreciated from the drawing, electrode 5 is situated at the base of the cavity interior while electrode 6 is situated to one side of the cavity, with a portion of the electrode 6 adjacent the cavity orifice or exit. Ground electrode 7 is spaced across the cavity exit from electrode 6, as shown. Thus, electrodes 5 and 6 define a first spark gap across a portion of the cavity interior and electrodes 6 and 7 define a second spark gap across the cavity exit.
The spark plug 1 embodying the invention operates as follows:
Arcs are struck simultane
REFERENCES:
patent: 1399166 (1921-12-01), Springer
patent: 2543961 (1951-03-01), Feichter
patent: 3567987 (1971-03-01), Schnurmacher
patent: 3719851 (1973-03-01), Burley
patent: 3908145 (1975-09-01), Kubo
patent: 4275328 (1981-06-01), Watanabe et al.
DeMeo Palmer C.
National Research Development Corporation
Razavi M.
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