US1671740A - Spark plug - Google Patents

Description

May 29, 1.928. w. L. PHILLIPS SPARK PLUG Filed March' 1, 1922 Patented May 29, 1928.

WILLIAM L. PHILLIPS, OF BROCKTON, MASSACHUSETTS.

SPARK PLUG.

Application ined Maren 1, 1922. j serial No. 540,317.

This invention relates to improvements in sparkplugs. More especially it relates to sparkplugs of the type comprising an auxiliary or subsidiary gap in the ignition circuit. The main purpose of all spark plugs is the transmission of a current to'` a place Where it can be caused to ignite a charge of explosive gases Within an engine adapted to utilize the power developed by such explosion. To this end, the spark plugs now in use have supplied the means whereby the current from a magneto or coil is conducted along an insulated electrode into the chamber of the cylinder, there caused to jump a gap to the wall of the plug from whichl the current may pass olf, usually into the engine walls which actas a ground circuit back to the source of potential. The important function of the spark plug isto conduct the current so that it will positively jump the gap, and not become short circuited in any manner before doing so. To insure this result the incoming electrode is usually encased in a substantial insulator, for practically its entire length. This insulator or core is usually made large and heavy in order to withstand both the pressure of the electrode, due to the latters expansion when heated, and the severe strains imposed `by Vcompression 1n assembling the parts of the plug; and as a result, the'core occupies nearly all the space within the plug, almost to the end of the electrode. It thus furnishes a convenient surface for the deposition of solid products been found under these conditions, that if the energy of the current is increased at the instant the spark would ordinarily jump, that it actually will jump the gap in'spite of the fouling. effect already described. As a means for increasing the energy available for ignition to overcome the -fouling effect,"a second or subsidiary ga has been interposed between the principe gap and the source of energy, with some satisfactory results; but, so far as I am aware, this subsidiarygap has never been utilized to its greatest capacity. It is usually found in one of three places; integral with the plug; at the Cplug, but not integral with it; or remove from the plug at a point Within or near the distributor. The iirst of these 10- cations is undoubtedly the most desirable from the viewpoint of electrical efficiency, inasmuch as its action with wrespect to the principal gap is so near the latter that the evil of dissipation is reduced to its minimum. But when placed integral with the plug it `has been the practice to leave the subsidiary gap either open to the air, or inclosed in an air-tight container; and its purpose and effect have been to overcome the short-circuiting effect ofdeposit and thus enable a spark to jump the p`rincipal"`gap. The action of the subsidiary gap, however, has in no way been utilized either to prevent the creation of such depositorto break it up and eliminate it after its formation has begun. `In contrast with this merc effort to surmount the evil conditions due to` fouling and to operate more orless effectively in spite of them, it is an important purpose of the present invention to get' rid of or to prevent the fouling. y

It is amongthe objects of the invention to so construct a spark plug that both the principaland subsidiaryl gaps are Within the explosive" mixture, whereby the spark across each gap may be utilized to fire the charge, thus at east doubling the igniting effectiveness of the plug. Other objects ofthe invention are, to intensify the principal spark` by the use of the subsidiary gap-in the circuit; to augment the intensifying eii'ect of the subsidiary gap by placing it in a. medium which is under compression and thus of increased density corresponding to a greater break-down voltage; to provide means by which the subsidiary gap may be adjusted both when the engine is idle and while running; to utilize t-he explosion caused by the auxiliary spark to clean an internal electrode and prevent deposit thereon of carbon or oil and, if desired, to clean an electrode directly connected with 4the outside conductor; to provide means permitting the auxiliary spark and its resultant explosion to be visible, thus signalling the lili llf)

actual firing of the explosive charge; to provide an insulated support for the internal electrode which shall be easily molded, light and self-cooling; to so position this insulator within the plug that it will be subjected to substantially equal degrees of heat and pressure on its opposite surfaces; and to so arrange and dispose the several parts of the plug as to provide a closed passage through the plug which may be opened when desired to permit priming of the plug, the testing of the compression, or the utili-y zation of the latter for tire inflation or other purposes.

These various objects are attained by supporting within a hollow of a spark plug a separate insulated internal electrode to which the current may jump from the external electrode across the subsidiary gap and from which it may jump across the principal gap, the said hollow constituting a part of the explosive chamber of the engine in which both gaps are filled by the gaseous mixture under compression. The support for this isolated electrode is provided with a passage through which the gases are foi'ced during the compression and expansion strokes of the piston, the passage being so arranged as to cause the moving gases to act as a cleaning agent on the internal electrode, the inner portion of the external electrode and on the support itself, thereby preventiner any undue deposit of the products of comiustion and eliminating any fouling or short circuiting of the plug. The walls of the plug surrounding the region in which the subsidiary gap is located may be made non-transparent,

or transparent or provided with windows, through which the igniting of the charge may be seen. The terminal of the plug to which the outside conductor is attached comprises elamping means for holding an upper or external electrode in adjustable relation to the internal electrode, and is so arranged that it may be withdrawn slightly n the plug to open a restricted passage thercthrough from the cylinder chamber to the atmosphere, or may vbe wholly removed to allow a compression gauge or air pump to be attached. In the embodiments shown in the accompanying drawings, various applications of the invention ai'e shown, but it is to e understood that these adaptations are merely illustrative. It is intended that the patent shall cover by suitable expression in the appended claims whatever features of patontable novelty exist in the invention disclosed.

Referring to the drawings:

Figure 1 is an elevation in medial section showing one form of plug embodying the invention Figure 2 is a plan in section on line 2-2 of Figure 1;

Figure 3 an elevation, partly eut away to a medial section, showing a modification;

Figure 4 is a horizontal section on line 4 4 of Figure 3;

Figure 5 is an elevation of a detail of another modi tication;

Figure (i is an elevation in medial section of a plug showing other modifications in the design and arrangement of the parts;

Figure 7 is a plan of Figure 6 in section on line (3f-6;

Figure 8 is an elevation in section showing a modified foriii of the plug terminal; and

Figure 9 is an axial section of a further modification of the invention.

In the drawings, a spark )lug base 10, threaded exteriorly at one en( for engagement with an engine casing (not shown) is bored throu hout its ,length to permit an internal con( uctor or electrode 12, to be snpported axially therein by a tubular insulating element 14, hereinafter called a core, having a flange head and holding portion seating on the upper edge of tliebase, and a thin walled tubular body portion 16 projecting within the base to form an insulating sleeve about the electrode for a considerable portion of its length. This internal conductor is secured to its support by clamping nuts 18, one of which presses insulating element, and the other of which rests against the under surface of the same, in the dee recess 22 within the bod portion 16, which ias the aspect of an annu ar chamber about the electrode 12. The lower end of the latter is near a sparking terminal 24, extending radially inward from the wall of the base being separated therefrom by a gapy a hollow, iion-ctuiducting cap or cover 32` held tightly in register with the insulated core 14 by a collar 34 threaded on the upper exterior surface of the base 10. This collar is flanged inward at its top to engage anr external flange around the bottom of the cap, so that upon the collar being turned on its threads it will clam the cap 32, the insulated su port 14, an the base firmly together, t ere being suitable gaskets or washers between the abutting surfaces to make the joints leak-proof under the working pres- Sures in' the cylinder, `The chamber 35 ofV j on the topl surface of the head of the said iolding and the cap 32, is connected with the annular chamber 22 by a series of holes 36 through the head ot' the insulating core, constituting Y passages tor the admission of gas :from the engine cylinder to the chamber in the top ol` the plug, and for its'expulsion. s

`The upper or external electrode 30 is held in axial alignment Withina sleeve 258 which passes through'the top ot' the cap and is securely clamped thereto by a nut 4l) threaded exteriorly on the sleeve, the threaded portion ot' the latter extending upward to form a stem for a supporting nut l2 Whose body portion engages the. stein, and through which the electrode pro-jects and to which it is locked by the locking nut le on the protruding end ol" the electrode. through the sleeve 38 is larger in `cross section than the electrode 30, so that the latter is surrounded by a small annular` `space Which opens into the chamber at Yone end, and at the other is closed by the tight lit of the stem inthe supporting nut when the latter isscrewed down to its limit on the sleeve 38. This space, however, may be vented to the atmosphere, upon the supporting nut being unscreweda short distance,`

there being radial holestG through the body of thenut close to its head which Will connect with the space left above the end of the sleeve 38 when the nut is backed a..

thread or two. It it is desired to prime the cylinder, the supporting nut, and with it the upper electrode, may be entirely removed from the sleeve 3S. The liquid gasoline, ether or other priming substance may then be poured into the top ol. the plug, whence it will pass through the chamber 35, passages 36, chamber and the bore of the plug into the engine cylinder. This mode of priming is very useful in that the liquid in passing through the plug dampens surfaces in the immediate vicinity of the' gaps whereby upon occurrence of the sparks across the gaps an explosion vvill of certainty occur. The removal ot' the supporting nut and electrode also enables a gaugeto be attached to thestem for testing jthecompression o-tthe cylinder; or if a pump is at-` s tached, instead ot a gauge, the pressure of the cylinder `may be utilized to operate the pump for blowing up tires `or doing otherl useful Work.

The terminal ol"` the outside conductorv :from the source' of electric Senergy may be slipped around a neck portion of the locking nut 44, or may be clamped between-this nut and a binding nut 48 screwed thereon, or

may be clipped over the top end oftheV binding nut its lf. i s Whenthe plug has been 'placed in the en-` gine ycylinder head,` and the compression stroke takes 'place the explosivemixtureis forced into the bore of the spark plug base and thence through the passages 36 intothe directed` to this particular plu The holev able `timing device and distributor the elecs trofnurtive force of the ignitionsystem `at a favorable time tor the igniting orthe charge.' Art the innerterminus oftheex-` `another slnirlrjuinps Vthe principal gap between thc terminal of the internal. electrode l2 and the terminal The. action isso rapid that the sparks are almost si1nultanons; and even though the gases in the upper chamber are actually ignited first the second spark occurs before the burning has beentransmitted to the gases about the sec ond` gap, so thatthe latter spark also sets lire to the explosive mixture. Thus two sep arateigniting sparks are provided by one circuit through the plug, one of which, the principal, is intensitied'by the other. This is particularly so in a plug embodying the present invention because ofthe fact that' the auxiliar gap is through a mixture ot', gases under compression ofthe cylinder.` As the density ot a gas is directly proportional to itsl pressure, and its resistance is directly. proportional to its density, it fol lows that theenergy required to overcome the resistauceiof a gap thus under compression is substantially larger thanit'the gap` were iu freev air or merely ineased in an airtight chamber. When'the increased energy required to overcome the resistance of the subsidiarygap is built up and the current leapsV across this gap, p aeticallyall `of this energy is then available for intensifying the spark across the principal rap, and as a result the principal spark is ighly energized and its el'ectiveness'increased for ignition of `the engine charge. i

The expansion ot' the burning gases in the chamber 35 causes them to pass down rapid` lyl througlfi the passageways 36 into the chamber 22and thence along past the eleotrode A12 into the engine cylinder` This 76 tei-nal electrode it buildsvup,r momentarily,

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high `speed of flow ol the gas through the -it may easily be removed by unscrewing the nut 42 until the radial holes lr6` vent the space `to the atmosphere. The degree of y lo longitudinal movement of this nut is so slight that even though the gap 28 be increased by the unscrewing of the nut 42 and the consequent movement of the upper electrode, the spark will continue to jump and the explosion to occur; and the pres-` sure resulting from the explosion in the chamber 35 will force any solid matter in the space about the electrode out through the holes 46.

In order that the operator may see that the plug is properly functioning, transparent means is provided in the top of the plug through which the sparking across the subsidiary gap and the flash of the resulting explosion are visible. The cap or cover 32 shown in Figure 1 Inay be made of any suitable transparent material such as glass especially made to withstand heat and pressure changes. In Figure 3,`a modified form of a top is illustrated in which a cylindrical transparent 'shell 50 is interposed between the support 14 of the lower electrode and an insulated support 52 of the upper electrode,

the' aligning collar 34 being perforated as at 54 to provide peep holes to the chamber 35. In Figures 6 and 9 a still different method is shown whereby a glass window 56 Visheld against an annular seat in a sleeve 58 by-means of the explosion chamber 35 and windows 54 thereof in that the nature of the combustion in the cylinder can be ascertained by the color of the flame seen in the chamber of the plug. It has been found in practice that the color o-f this flame varies in accordance with the kind of explosion taking place in the cylinder. If a very rich mixture is used the flame will be of one color; if a thin or poor mixture is employed the flame will be of a different color; and if kerosene or other substances are added to the gasoline, this also causes changes in the flame color. Accordingly, by a series of experiments a color chart may be developed, based upon the flame colors oli-different explosive mixtures which will show the relative efficiency of various fuels; and thereafter a comlmrison of the colors of the flamesl produced in the plug with the listings on the chart, will enable the user of the plug to know the conditions existing in the cylinder at the time the explosion therein takes place.

A further modification is illustrated in Figures 3 and 4, wherein the lower electrode 12" is made in the form of a hollow stem or tube 'fitting tightly within the central bore o f the insulating element 14. The upper end of this electrode is preferably substantially flush with the top surface of the core, while its lower extremity extends below the core close to the sparking terminal 24. The opening through this tube constitutes the transfer passage for unfred gases from the engine cylinder to the u per chamber of the plug, and for the burmn gases' from the upper chamber back to t e cylinder. In consequence of the latter transfer and because of its proximity to; the lower spark gap, the protruding end of the tube becomes hotand serves to heat the unburned gases as they pass upward through it into the chamber 35, thus' aiding their ignition, and by so doing, permitting poorer grades of fuel to be used than has heretofore been possible because of inability to fire them under normal temperatures cxistino' in the cylinder. In a plug equipped with this particular type of lower electrode the passa e to the upper chamber may be restricted y moving the upper electrode 301V toward the hollow conductor 12"' thus reducing the effective opening of the latter and at the same time varying the sparkA gap. By this means, the amount of gas entering the upper chamber can be regulated to any desired amount and may in fact be entirely cut off by screwing down the upper electrode 30 until its conical end seats tightly on the rim of the tubular conductor. This, of course,

will also do away with the auxiliary spark gap and would not be the most desired manner of using the plug, but such setting could be adopted advantageously in case the transparent cylinder 50 should become accidentally shattered and could not be conveniently replaced at the time of such accident. By thus closing the passage to the upper chamber the plug could then function as the ordinary single gap spark plug.

In they type of plug shown in Figure 1, and in the various modifications hereinafter described, the upper spark gap may be closed by bringing the adjacent ends of the electrodes together and making them electrically integral. This would make the upper chamber a mere flash chamber inwhich the gases would be fired b the single spark occurring within the cylin er but even when thus'used, the plug would serve, as lalready described, to indicate by the color of the flame the nature of the e'xplosion'qecurring in the cylinders.

In Figure 5 a modification of the support for the internal electrode is shown in which the sleeve portion y16 isreduced in diameter and set close to the electrode, and the passages 36 are provided. through the flange portion communicating with the lower chamber on the outside of the sleeve 16. In Figure a still different form of support 16 is shown, in which the support has an axial passage throughout its length, in the midst of which the electrode is supported by a perforated disk member 64 set into the walls ofthe insulator, through the perfrasures, nor are they under high'temperaturel at one end and relatively lowtenipcrature at the other. TheV cores are heldin place `by direct clamping pressures onopposite sides of their flanged portions; `and the pressure on the nuts or othermeanswhich sup-` port the electrode in place are equal and opposite in elfect. Since the explosion occurs above and below and around the core at practically the same instant, the pressure changes upon and the temperature changes ofthe insulator are substantially uniform.`

lVhen the cylinderis being charged the movement of the fresh gases through the plug and passageways vof the `support into the upper chamber, tend to uniformly cool the porcelain and prevent its ever becoming overlieated though entirely located within the exploding chamber. 1 e

` In Figure 6 the upper or external electrode 30 is shown arranged at the side "of the plug casing instead `ofat the top. Figure 9 also embodies this arrangement but shows a further modification of the invention wherein the internal electrode 12 is supported at the top of the plug sothat it projects longitudinally through the bore which is substantiallyunobstructed by any supporting means, except where tightly closed at its upper end. The current is brought into the plug fromthe side through the external electrodeBO, or ifaduplex system of `ignition is used, another electrode 30 may conduct the second current `to the internal electrode; "If it were desired to use a system wherein, the ignition circuit was to be entirely insulated from the engine. and

not use the "latter as a ground, the forni of plug shown in Figure 9 would `lend itself most conveniently'to such an arrangement, in that tlie internal electrode 12` could be entirely removed, the current conducted through the plug by the external electrodes 30 and 30, the spark occurring across the gap between their ends located'in the bore of the plug.`

Figure 8 shows a modification of `the upperelectrode and its` connections, wherein the electrode extends upward so that its external endmay be engaged by a screwdriver or other tool and the electrode moved foradjustment while the engine is running. The external conductor would be attached to the lock nut 44 or between this nut and the binding nut 48. both of Whichwould be removed on the electrode away from the supporting nut 46, so that the electrode could be withdrawn or inserted until the proper e spark gap.

gap was ascertained `under running conditions, after which the lock nut could be seated against the supporting nut to fix the electrode in the adjusted position, and then the binding nut turned down to clamp the conductor. e e

Although referred ltoas being in a` vertical position, it is evident thatthe plug of the invention may beset otherwise, at pleasure.` If for any reason the current` is momentarily cut olf from a spark plug of type hitherto known, and the engine allowed to run awhile Iwithout a spark occurring, such a plug may become foul by having its gap filled with lubricating oil that has leaked by the piston rings, and itis usually necessar to remove and clean the plug before it willI again properly function. But with a plug of the type herein described the upper gap, beingprotected from such oil leakage would tire the charge as soon as the circuit was restored.` Upon the first firing, the lower gap would be cleaned and the normal double-fire condition restored.

I claim as my invention: e

l. A spark plug for the cylinder of an internal combustion engine, having spark gap electrodes in combination with a chamber into which explosive mixture of the engine cylinder may be .x forced past said electrodes; and other spark gap electrodes within said chamber, in series with the tirstmen- .l gine cylinder may be forced past said electrodes; and other spark gap electrodes Within said' chamber, in series with the first mentioned electrodes, the spark of which `is adapted to ignite said mixture within said chamber, there being a partition separating the spaces where the two gaps are, support- `ing the conductor which runs between the gaps, and having an opening for passage of gases` to and from the second mentioned e forced` to be` ignited by the ino 4. A spark plug for the cylinder of an internal combustion engine having con` ductors arranged to form two spark gaps in series, both being set in space accessible to mixture of the engine cylinder, and one of them being between the other and the engine cylinder, whereby the ignition of mixture by that which iS more remote from the cylinder causes a rush of gases past the other into the cylinder.

5. A spark plug for the cylinder of an internal combustion engine having conductors arranged to form two spark ga s in series, both being set in space accessib e to mixture of the engine cylinder, and one of them being between the other and the engine cylinder, whereby the ignition of mixture by that which is more remote from the cylinder causes a rush of gases past the other into the cylinder, there being a partition arranged between the 'spaces wherein the two gaps are located, penetrated by a pas sage for transfer of the gases from one space to the other.

6. A spark plug, adapted to have one end inserted in the wall of the cylinder of an internal combustion engine, `having spark gap electrodes; and a chamber, within the plug, outside of the engine cylinder, having communication with the engine Vcylinder through one of said electrodes for passage of gases; said chamber containing said spark gap electrodes.

7. A spark plug for the cylinder of an internal combustion engine having a plurality ot chambers accessible to explosive mixture from the engine cylinder, and havingspark gap electrodes in each chamber whose spark ignites the explosive mixture therein.

8. A spark plug for the cylinder of an internal combustion engine having conductors arranged to form two spark gaps in series lengthwise of the plug, both gaps being set in spaces accessible to mixture of the engine cylinder; one of said spaces being outside of the engine cylinder.

9. A spark plug for the cylinder ofv an internal combustion engine havinv conductors arranged to form two spark gaps in series, both being set in space accessible to mixture of the engine cylinder and one of the conductors which constitutes a spark electrode being mounted movably in the plug, toward and from the other electrode of the same gap; and external means to move and to fasten said movable conductor.

10. A spark plug for the cylinder of an internal combustion engine having a plurality of intercommunicatin chambers in the same plug, each accessib e to explosive mixture from the engine c linder; and spark gap electrodes arrange for ignition of the mixture in each of said chambers.

11. A spark plug for the cylinder of an internal combustion engine, having spark gap electrodes arranged to cause ignition of `the explosive mixture in the cylinder, combined with means comprising a chamber in said plug connectlng with sald cylinder' and with the outside of said plug, and a closure for said outside connection adapted to be 65 opened to vent said chamber. o

12. A spark plug for the cylinder of an internal combustion engine, 4aving spark gap electrodes arranged to cause ignition of the explosive mixture in the cylinder, combined with a chamber in said plug, a passage connecting said chamber with the en eine cylinder wherein gases may pass to and rom said chamber, and ymeans for regulating the flow of gases through said passage. y

13. A spark plug for the cylinder of im internal combustion engine com rising conductors arranged to form multiple s .ark gaps, a chamber in the ug removed rom the cylinder and havln communication therewith through the hpliw of one of said conductors, whereby gases ma pass to and from the cylinder to the `cham er; a gap in` said chamber between the end of the hollow conductor andk another conductor; the said other conductor being adjustable whereby the gap and the openin of the hollow. conductor into fthe cham er may be varied simultaneously.

Y 14. A spark plug for the cylinder of an internal combustion e v ine, comprising conductors arranged to orm multiple `spark gaps; a chamber in said plug removed from the cylinder and havi communication therewith through the h ow of one of said conductors whereby gases may pass to and from the cylinder i a ga A arranged in said chamber, across which thpe current jumps to .ignite the gases therein, thereby causirg4 a pow rush of burning gases through the ho conductor to the cylinder; the said burning gases heating said hollow conductor which in turn gives up heat to the unburned gases forced therethrough to the chamber.

15. A. yspark plug for the cylinder of an internal combustion engine, having an internal chamber; spark gap electrodes arranged.

to vform a sparkgap therein; a. passage connecting said chamber with the engine cylinder for transfer of gases from one to the other; one of said electrodes being arranged in said passage whereby it is cleaned by the gases passing to and from said chamber.

16. A spark plug for the cylinder of an internal combustion engine, having an internal chamber; spark gap electrodes arranged to form a spark gap therein; a passage connecting said chamber with the engine cylinder for transfer of gases fromv one to the other; another passage connectin said chamber with the atmosphere; an means for regulating the opening of the last mentioned passage.

17. A spark plu having a hollow body portion adapted `to be inserted in the wall of an internal combustion engine; insulating mcmberssecured to said bodyportion, forming a chamber; spark gap electrodes sup# ported by said members providing a spark gap in said chamber; and a passage through one of said members connecting said cham-V ber with theengine cylinder for transferV of gases from one to the other. i

18. A spark plug having a hollow body portion adapted to bel inserted in the wall of an internal combustion engine; insulating members secured to said body portion forming a chamber; spark `gap electrodes supported bysaid members providing a spark gap in said chamber; a passage through one of said members connecting said chamber with the engine cylinder for transfer `of gases from one to the other, and a passage through another or said members communicating with the atmosphere; the said passages and chamber alfording an outlet for the gases; and means externally on said plug for closing said outlet. i g

19. A spark plug, adapted to have one end inserted iii the ivall of the cylinder of an internal combustion engine, having spark gap electrodes; and achainber, within the plug, outside of the engine cylinder, having communication with the engine cylinder; one of said electrodes being hollow and having side openings through which the gases are jetted against an internall Wall of the plug to clean it. i

2l). A spark plug for an internal combustion` engine having hollow insulating members whose hollows constitute a passagel between the engine cylinder and the atmosphere; a sleeve through one of said members; an electrode inovably supported on said sleeve and adaptedto be moved to 'close said passage; and another electrode in the plug forn'iing lwith said movable electrode a sliiark gap. i

21. A' spark plug, adapted to have one end inserted in the Wall of` the cylinder of an internal combustion engine, having spark gap` electrodes in combination with a chamber, within the plug, outside of the engine cylinder, and having' connection with the engine cylinder; one of said electrodes having a 'passage through it for transfer of Huid to said chamber.

2Q. A spark plug having a bo'dy portion inder of an internal combustion engine; a

chamber in said plug beyond said body portion and outside of said cylinder; electrodes forming a spark gap vin said chamber for `ignition of gases therein; and a passage through said body portion connecting said chamber with the cylinder for transfer of gases from one to the other; said passage having awall adapted toabsorb heat from the hot gases passing from the chamber to the cylinder, and to give up heat to the cooler gases passing trom the cylinder` to the chamber. i i

` .2A/L1A sparkplug for the cylinder of an internal combustion engine, having a chamber therein outside of the engiiie cylinder; electrodes forming a spark gap in said chamber for ignition of gases therein; and a relatively 'long passage through said plug connecting said chamber with said cylinder for .transfer of` explosive mixture to said chamber and for transfer of burning gases from said chamber tothe cylinder;the Walls of said passage being of such length as to permit transfer of heat thereto during passage of the burning gases and to permit transfer of heat therefrom during passage of the explosive n'iixture. y u

v25. A spark plug, adapted to have one end inserted in the wall of the cylinder of an internal combustion engine, having spark gap electrodes in combination with a chamber, within the plug', having connection withthe engine cylinder; one of said electrodes being hollow to permit entrance therein of hot gases wherebyI the electrode is heated and cleaned.

26. A spark plug, adapted .to have one end inserted in the Wall of the cylinder. of an intei-nal combustion engine, having spark gap electrodes; and a chamber, within the plug, having communication with the engine cylinder; one of said electrodes being hollow and having an opening into said chamber ivheieby gases may pass through the electrode to and from said chamber.

` 2T. T he combination with an internal coinbustion engine, of a spark plug extending through a Wall `and into the combustion space thereof, said plug being provided with spark gaps positioned one on each side of said Wall and further provided with a chamber adjacent the outer gap, a restricted opening leading from .said chamber and into the'coinbustion space ot said engine adjacent the inner gap, whereby the gases exploding in the outer Vchamber are forced through said opening with high velocity and caused to contact the electrodes of the inner gap and purge the saine, substantially as described.

The combination with an internal come bustion engine having a combustion space, a

kspark plug formed outside of said space with,

a combustion chamber having a restricted opening communicating with said space, and a pair of spark gaps arranged in series and disposed one on each side of said restricted opening, substantially as described.

29. A spark plug for internal combustion engines comprising a body formed with a restricted chamber adapted to communicate with the combustion space thereof, a grounded terminal carried thereby, an electrode insulated from and extending through said body into said chamber, and a neutral electrode insulated from said body and interposed between said grounded terminal and said electrode.

.30. `A spark plug for internal combustion engines comprising a. body formed with a restricted chamber adapted to communicate with the combustion space thereof, a grounded terminal carried thereby, an electrode insulated from and extending through said-body into said chamber, and a neutral electrode mounted within said chamber ad- 'jaceiit said electrode extending through said restricted chamber adjacent said grounded terminal.

3l. A spark plug for internal combustion engines comprising a body formed with a restricted chamber adapted to communicate with the combustion space thereof, and electrodes arranged in series and insulated from said body providing a plurality of spark gaps. L

32. A spark plug for internal combustion engines comprising a body formed with a combustion chamber adapted to communicate with the combustion space thereof and electrodes mounted in said combustion chainber and arranged in series providing a plurality of spark gaps. i

33. A spark plug, adapted to have one end inserted in the wall of the cylinder of an internal combustion engine, having an insulator with a chamber, Within the plug, having coniii'innication with the engine cylinder;

` electrodes forming a spark gap in said chainbei'` one of said electrodes being hollow and having an opening into said chamber whereby gases may pass through the electrode to and from said Chamber.

34. A spank plug having a Vbody portion dapted for insertion in the wall of the cylinder ot an internal combustion engine, and having spark gap electrodes; a chamber within said plug, beyond ysaid body portion and outside of said cylinder having communication withthe cylinder; and other spark (Isp electrodes, within said chamber, in series with the first` mentioned electrodes.

35. A spark plug having a body portion adapted for insertion in the wall of the cylinder of an internal combustion engine, and having conductors arranged to form two spark gaps in series lengthwise of the plus, both gaps being set in spaces accessible to explosive mixture ol the engine cylinder; one ofsaid s )aces being outside of the engine cylinder an beyond said body portion.

`36. A.V spark plug having, in con'ibinatiom an inner conducting jacket adapted for inseition in the wall ot' the cylinder lof an internal combustion engine and having a spark gap terminal; an outer casing adapted to be positioned outside of the cylinder and having a chamber; aii insulating element extending into the jacket and disposed between the acket and the outer casing and having a passage communicating with' the chamber and with the cylinder for transfer of gases between the chamber and the cylinder; an electrode cariied by the outer casing having a `.spark gap terminal in the chamber; a second electrode, insulated fromy the first mentioned electrode and mounted in the insulating element and having a spark gap terminal cooperating with the first mentioned terminal to form a spark gap in the chamber; the second electrode being insulated bythe insulating element from the jacket, and having a second spark gap terminal cooperating with the jacket terminal to form a spark gap in the cylinder; whereby the said spark gaps are disposed in series.

Signed at Boston, Massachusetts, this twentieth day of February, 1922.

WILLIAM L. PHILLIPS.

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