US2981859A - Peras - Google Patents

Description

L. PERAS April 25, 1961 LOW-TENSION SPARK PLUGS FOR INTERNAL COMBUSTION ENGINES Filed April 1, 1958 LOW-TENSION SPARK PLUGS FOR INTERNAL COMBUSTION ENGINES Lucien Pras, Billancourt, France, assignor to Regie Nationale des Usines Renault, Billancourt, France Filed Apr. 1, 1958, Ser. No. 725,618 Claims priority, application France Apr. 29, 1957 7 Claims. (Cl. 313-131) The present invention relates in general to spark plugs of mternal combustion engines and has specific reference to an improved low-tension spark plug.

It is already known to constitute the sparking element of spark plugs utilized for igniting the fuel mixture in internal combustion engines by the discharge of a condenser in the form of a pair of electrodes spaced .004" to 0.012" apart, this gap being occupied by an insulating member on which the ignition spark is caused to slip.

The assembly comprising the electrodes and insulator is usually called cartridge.

Now it is the essential object of this invention to provide an improved spark plug of this general character and more particularly the above-defined cartridge which is characterized 'by a specific arrangement of the electrodes and insulator whereby the useful life and regulari-ty of the spark plugare increased to a substantial extent.

embodiment of a low-tension spark plug constructed in accordance with the teachings of this invention.

In'the drawing, the electrodes of the spark plug are designated by the reference numerals 1 and 2. The electrode 1 consists of a disk of refractory metal such as tungsten or thoriated tungsten, and the other electrode 2 consists of a hollow cylinder also of refractory metal. The electrode'z is formed with an axial bore provided at one end with a cavity or counterbore forming a shoulder 3 and adapted to receive an insulating washer 4 constituting the spark supporting member seated on said shoulder. The diameter of this washer is very slightly smaller than that of the electrode 2. The interior of this electrode 2 is lined with insulating material 5 such as boro'silicated glass up to the level occupied by the washer 4 bearing partly against this insulating lining and partly against the metal of the electrode 2. The insulator 5 may be fitted by compressing glass in the electrode carried by a jig. The electrodes'l, 2 are not necessarily of straight cylindrical shape with an annular cross-section, as the cylinder section may be designed to suit specific requirements of the combustion chamber. For the sake of economy the electrodes may be made not entirely of solid refractory metal but formed, for example, by welding a thin annulus of tungsten or thoriated tungsten on a steel body. The insulating washer 4 fits exactly in its recess or counterbore and may be slightly greater than this recess as measured in the axial direction; in this case the electrode 1 may have a greater diameter, or a diameter tube 10". ,the two electrodes by properly stacking at the upper end equal to or less than that .of the insulating washer. If desired, its height may be equal to or smaller thanthat of the recess; in both cases the diameter of this electrode 1 is smaller than that of the diameter of washer 4. The spark-supporting insulator isnot necessarily a flat hollow cylinder as the chief requirement is that its shape accommodate that of the electrode; besides, it may also completely fill the grounded electrode 2 and form a substitute for the insulator 5. The spark-supporting insulator 4 is preferably made of refractory material having a reliable stability up to 1000 C., that is, adapted to be heated to this temperature without melting, decomposing or undergoing any physical deterioration whatsoever; thus, porcelain, sintered alumina, clay-bound alumina, and

the like constitute efficient materials for this purpose.

If desired, insulating materials of high dielectric capacity may be used to-advantage. The interelectrode gap e is of the order of 0.012" to 0.08" according to the type of insulating material utilized. The spark plug body 6 consists of a metal member insulated by a porcelain filling 8 and a Bakelite or like insulating cone 9 from the central steel tube 10 in which extends the current lead-in rod. The rod 7 is axially displaceable in The insulator is constantly pressed between of the central rod 7 a plurality of spring-steel dished washers 11. These washers are disposed by pairs with their concavities facing each other and they exert a certain pressure against a sealing gasket 12 for example of .polytetrafiuoroethylene; this pressure is obtained by means of an adequate nut 13 screwed on the rod 7.

Finally, the sparkingsurface may be enamelled with a suitable spark-supporting composition.

I claim: 1. In a low voltage spark plug having a tubular member, a spark-plug cartridge removably mounted in said body member comprising, a tubular first electrode disposed concentric internally of said tubular body member nular inner surface of said first tubular electrode defining 50- said counterbore and having a substantially flat face coplanar with a substantially flat end of said electrode corresponding to said electrode end extending axially out of said body member, a disc electrode mounted coaxially with said tubular electrode and having a transverse dimension smaller than said insulator forming a circumferential gap of uniform dimensions between the disc electrode and the tubular electrode thereby forming a sparking zone of uniform dimensions, and an electrically conductive, axially displaceable, member disposed extending axially in said tubular electrode and said body member and having a mushroom head for removably holding the disc electrode snug against said coplanarface surface of the insulator, means comprising a plurality of dished cooperatively disposed spring elements disposed externally of the tubular body member for adjustably applying an axially directed tension to said electrically conductive member for causing the head thereof to apply pressure to said disc electrode in a direction pressing the disc electrode against said insulator, and an insulating composition circumferentially of said electrically conductive member filling said axial bore of the first electrode and extending axially in said tubular body member.

2. A low voltage spark plug according to claim 1, in which said insulator comprises a refractory material and is capable of remaining dimensionally stable at elevated temperatures at least-to 1000 centigrade.

3. A low voltage spark .plugaccording to claim .1, in which said insulator comprises a ceramic having a dielectric constant greater than 50. i

4. A low voltage spark plug according to claim 1, in which said insulator is enamelled at least on said sparking zone with a spark-supporting enamel.

5. In a low voltage spark plug having a tubular member, a spark-plug cartridge mounted in said body member comprising, a tubular first electrode disposed concentric internally ofsaid tubular bodymember at one end thereof and extending axially externally thereof at saidend, said tubular electrode extending axially into said body member substantially a greater distance than the axial distance it extends outwardly of said bodymember, said tubular electrode having an axial bore with a counterbore in one end of the bore forming a shoulder internally of said electrode, a washer-like insulator mounted coaxially with said electrodein said counterbore and seated on said shoulder, said insulator having a peripheral surface makingcontact with an annular inner surface of said first tubular electrode defining said counterbore and having a substantially flat face substantially coplanar with a substantially fiat end of said electrode corresponding to said electrode end extending axially out of said body member, a disc electrode mounted coaxially with said tubular electrode and having a transverse dimension smaller than said insulator forming a circumferential gap of uniform dimensions between the disc electrode and the tubular electrode thereby forming a sparking zone of uniform dimensions, andan electrically conductive, axially displaceable, member disposed extending axially in said tubular electrode and said body member and having a mushroom head for holding the discelectrode snug against said coplanar face surface of the insulator, means comprising a plurality of dished cooperatively disposed spring elements disposed externally of the tubular body member for adjustably applying an axially directed tension to said electrically conductive member for causing the head thereof to apply pressure to said disc electrode in a direction pressing the disc electrode against said insulator, and an insulating composition circumferentially of said electrically conductive member filling said axial bore of the first electrode and extending axially in said tubular body member.

6. A cartridge for a low voltage spark plug comprising, a tubular first electrode, said tubular electrode having an axial bore with a counterbore in one end-of the bore forming a shoulder internally of said electrode, a washerlike insulator mounted coaxially with said electrode in said counterbore and seated on said shoulder, said insulator having a peripheral surface making contact with an annular inner surface of said first tubular electrode defining said counterbore and having a substantially flat face substantially coplanar with a substantially flat end of said electrode corresponding to said electrode end having said counterbore, and a disc electrode mounted coaxially with said tubular electrode and having a transverse dimension smaller than said insulator forming a circumferential gap of uniform dimensions between the disc electrode and the tubular electrode thereby forming a sparking zone of uniform dimensions, and an insulating composition filling said axial bore of the first electrode.

7. A cartridge for a low voltage spark plug comprising, a tubular first electrode, said tubular electrode having an axial bore with a counterbore in one end of the bore forming a shoulder internally of said electrode, a washerlike insulator mounted coaxially with said electrode in said counterbore and seated on said shoulder, said insulator having a peripheral surface making contact with an annular inner surface of said first tubular electrode defining said counterbore and having a substantially fiat face substantially coplanar with a substantially flat end of said electrode corresponding to said electrode end having said counterbore, a disc electrode mounted coaxially with said tubular electrode and having a transverse dimension smaller than said insulator forming a circumferential gap of uniform dimensions between the disc electrode and the tubular electrode thereby forming a sparking zone of uniform dimensions, and an electrically conductive, axially displaceable, member positioned in assembly in said spark-plug extending axially in said tubular electrode and having a mushroom head for holding the disc electrode snug against said coplanar face surface of the insulator,

means comprising a plurality of dished spring elements References Cited in the file of this patent UNITED STATES PATENTS 963,334 Stonebridge July 5, 1910 1,110,813 Noble Sept. 15, 1914 1,272,954 Horning July 16, 1918 1,403,448 Ryder Jan. 10, 1922 2,605,754 Smits Aug. 5, 1952 2,760,099 Suter Aug. 21, 1956 FOREIGN PATENTS 22,517 Great Britain Sept. 28, 1910

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