US2859370A - Low-tension sparking plug for - Google Patents

Description

Nov. 4, 1958 L. PERAS 2,859,370

- LOW-TEN N SPARKING PLUG FOR INTERN coulBus N- INES Filed Jan. 19

Fly.

United States Patent Ofifice 2,859,370 Patented Nov. 4, 1-958 LOW-TENSION SPARKING PLUG FOR INTERNAL COMBUSTION ENGINES Lucien Pras, Billancourt, France, assignor to Re'gie Nationale des Usines Renault, Billancourt, France Application January 2, 1957, SerialNo. 632,089 Claims priority, application France January 12, 1956 8 Claims. 01. 313-131 It is well-known to technicians thatsparking plugs for internal combustion engines have been developed in which the sparks are produced by discharging the current delivered from a condenser across a relatively reduced gap of from 0.004 to 0.012" between'the two electrodes. This gap is filled by a mass of insulating material and the spark glances off its surface.

Generally, the assembly comprising the electrodes and k the insulator is called insert or cartridge.

This invention relates to low-tension sparking plugs and more particularly to improvements in the aforesaid inserts for sparking plugs of this character.

These inserts are characterized in that they consist of two metal electrodes in the form of coaxial hollow cylindxical members, the interval between these cylinders being kept to a constant value by an insulating cylinder filling without clearance the gap between the electrodes. A central hole is provided in the insulator for the dual purpose of permitting the assembling of the. insert components by clamping and feeding the current to one of the electrodes.

According to another feature of this invention, the sparking surfaces of the cylindrical members, which are slanted lie consequently at the desired distance or space from each other are so machined, before or after the assembling step, that they diverge radially so that the space between the electrodes is splayed outwardly.

Sparking plugs having this specific configuration, in accordance with the invention, are characterized by a rig useful life and operate regularly. They are also adtageous in that they avoid completely the frequent wback of low-tension sparking plugs whereby the k, subsequent to a certain deterioration of the insuor, occurs inside the insert and does not ignite the air- 1 mixture.

In the accompanying drawings:

Figure 1 is an axial section showing a first embodiment a sparking plug insert constructed in accordance with e teachings of this invention;

Figure 2 is a similar view showing a preferred method f assembling the component elements of the device of ig. 1; and

. Figures 3 and 4 are axial sections showing modified ,1 embodiments of the invention.

" In the drawing, Figure 1 illustrates, by way of example,

, a typical embodiment of the invention wherein the electrode 1 is connected to the distributor through the central rod 2; the other electrode 3 is earthed through the spark ing plug body (not shown) in which it is force fitted or otherwise secured. It will be understood that the electrodes may be cylindrical or may have a plurality of flat peripheral surfaces, as for example, they may be prismatic. The insulator 4 fills completely the inner space of the two superposed but spaced electrodes, and the sparks occur only on the massive portion 5 thereof.

As illustrated, the registering edges of the two cylinders are bevelled to form a gap splayed outwards, so that 2 V the spark will occur on the free lateral surface of the insulator 4. e

Thisinsulator may consist, for example, of borosilicated glass according to the embodiments later herein described. a

In a specific embodiment, it is possible for example, as illustrated in Fig. 2, to position the lower electrode 1 into a hollow cylinder 6 of refractory steel, with a certain clearance therebetween, and subsequently introduce the upper electrode 3 for example after having interposed between the electrodes three detachable mica segments 7. The assembling step is completed by an upper cylinder 8 and a core 9 of refractory steel or graphite. Then the two electrodes 1, 3 are filled with glass powder, for example borosilicated glass, and the assembly is heated .to about 1.470 F., whereafter the glassis compacted by exerting .a certain pressure thereon by means of the piston 9 Upon cooling, the insulating material sets and finally, the insert is ejected, and any glasshaving been extruded in the sparking gap beyond the insulator surface is removed by a proper grinding operation. It will-be understood that the mica piecs 7, may be left on or can be removed from the assembled electrodesas desired. These mica segments or pieces 7 are of a dimension that does not interfere with the sparking zone of the assembled electrodes.

. Another possible embodiment of the present invention is illustratedin Fig.3 of the drawing wherein .the insulator 10 of the insert consists of a cylindrical body which may be moulded beforehand and accurately machined to size; the upper electrode is formed with an inner shoulder 11 permitting an arcuate relative spacing of the two electrodes. Y

Asanalternative, the narrowest portion of the spark gap is not defined .by the innercylindrical surface of the electrodes ;but lies atan intermediate'distance between this surface and the outer cylindrical surface of i the electrodes. This modification is illustrated in Fig. 4. If the insulator consists of a sintered mixture of glass and mica, the insulator may coincide with the narrowest portion of the spark gap by coating the lateral surface of the insulator body with powdered glass or lead silicoborate, or one of these powders in suspension in a liquid. Then the assembling step is performed during which the powder or paste fills the space 12, and finally the assembly 1. In a low tension surface discharged spark plug, a hollow tubular first electrode, a second electrode spaced axially of the first electrode, an insulator core disposed axially in the first electrode and substantially corresponding in diametral dimensions to the bore thereof and extending axially out of one end thereof, the second electrode being adapted to receive the end of the insulator core extending axially from the first electrode, said electrodes having registering slanted, sparking, end surfaces spaced axially of each other and diverging radially of the electrodes in a direction away from the longitudinal axis of the first electrode thereby defining a splayed sparking zone, whereby the insulator maintains the electrodes spaced in a fixed axial relationship.

2. In a low tension surface discharge spark plug according to claim 1, in which the core insulator comprises a sintered glass and mica mixture.

3. In a low tension surface discharge sparkplug according to claim 1, in which the electrodes are made of tungsten.

4. In a low tension surface discharge spark plug according to claim 1, in which the insulator core comprises borosilicated glass.

5. In a low tension surface discharge spark. plug, a

first hollow tubular electrode, a second electrode spaced insulator having peripherally 'exposed'surfaces in the space between'the slanted smracesorthe two electrodes thereby to maintain the two electrodes axially spaced in fixed relationship. 6. In a low tension surface dis'charge spark plug, afirst hollow tubular electrode, a'secondelectrode spaced axially of the firstelectrode; an insulator score disposed axially in the firstelectrode and extending'axially out of one end thereof, the'second electrode'being adapted to receive the end of the insulator core extending axially frorn t he first electrode, saidelectrodesfhaying' registering slanted, spark ing', end surfaces spaced'axially of each other'an diverging radially of the' electrodes in a direction" away from" the: longitudinal axis ofthe' first electrode thereby defining asplayed' sparking zone, and fnon=condfuctive means dis posed in the space"between".the' slanted surfaces of the two electrodes and having'an' outer diameter larger'than the inner diameter of the first electrodeiand' said Qatari diameter being smaller than the outer diameter "of the "first electrode. I

7. In a low tension surface discharge. spark pliigfa hollow tubular'first electrode, ajse'cond electrode spacedaxially of the first electrode, an insulator"c'ore disposed axially .in' the first: electrode"substantially corresponding with the' bore thereof and extending axiallyToiit of one i I from the longitudinal axis of, are electrode end thereof,"thesecond electrode being adapted to e'ceive' the end of the insulator core extending axiau nomthe first electrode, said electrodes having registerin'gfslante dj sparking; end surfaces: spaced axially of each other and divergingradially of thefel'ectrodes' in a direction away" 40 v V 4 defining a splayed sparking zone, and the core insulator having aportion having an outer diameter larger than -the inner diameter of the first electrode and said outer diameter being smaller than the outer diameter of the 1 first electrode in the space between the slanted surfaces of the two electrodes.

8. -In a low tension surface discharge spark plug, in combination, a hollow tubular first electrode, a second electrode disposed in axially spaced relation of the first electrode, an insulator core disposed axially in the first" electrode and extending axially out ofone end thereof,

the second electrode being adapted to receive the end' of a the insulator core extending axially from the .fir'st elec-, trode thereby to hold the two electrodes in axially spaced relationship, said electrodes having corresponding end, sparking surfaces disposed in juxtaposition axially of each other, said end surfaces of each of the electrodes being V+shaped and each having the apexthereof. disposed toward each other; and constitutingsthe point at which there; is the, least axial distance between :the. endcsurfaces, and thecoreinsulator havinga portion extending radially, into the, space, defined between .said end surfaces :of the I electrodes, said core portion having a: diametericorrespending substantially to the .diameter, of .the electrodes betweentwolpoints;wherein the axial distance between surfaces; whereby a .'splayed sparking zone isv defined between the electrodes,,andz.erosion of said coreportion does not impede. thetdi'scharge between said vend .sparking surfaces; atleast until {the core iserodedto an extent whereinthediameterof, said core portion corresponds to theIinnerdiameteLof'said first'electrode. a

i References Cited the, file of, patent r UNITEDSTATES-PATENTS 1 .503 I si i i .--'.-f---..-,-.-.i-r- --f r-1 5, 1

v :FQREIGN rwranrs 14.8907 Australia s Aug, 3,1950.

Images