US2122242A - Spark plug - Google Patents

Description

June 28, 1938. E, E, BIDWELL 2,122,242

SPARK PLUG I Filed Aug. 26. 1957' v f' zz/erzzr flu"! Z15 idwez Patente June 28, 1938 lTE AT SPK PLUG Earl E. Bidwell, Gary; lind., assignor to Productive Inventions, Inc., Gary, Ind, a corporation of Indiana Application August 26, 1937, Serial No. 161,098

28 Claims.

This invention relates to spark plugs constituting a part of the ignition systems of internal combustion engines or motors, and more particvide a novel construction and arrangement in.

spark plugs whereby the character and position of the spark is automatically determined by the operating conditions of the engine, in connection with which my improved plug is employed.

Another object of the invention is to provide -a novel construction and arrangementwhereby the life or length of service of the plug is materially increased, and wherein the necessity of frequent cleaning and adjustment of the points thereof is obviated.

Another object of the invention is to provide a spark plug of improved design wherein the position of the spark will materially facilitate starting of a cold motor, for example, and wherein the spark will automatically shift to a position to provide the most efficient operating conditions after the motor has warmed up.

A further object of the invention is to provide a spark plug of novel construction contributing to the efiicient operation of a motor at idling speeds, and the maintenance of the points of the plug in a clean condition to insure eflicient operation thereof.

A still further object of the invention is to improve devices of the character described in sundry details hereinafter referred to and particularly pointed out in the appended claims.

One embodiment of the present invention is I shown for illustrative purposes in the accompanying drawing, in which:

Fig. 1 is a vertical sectional elevational view of a spark plug embodying features of the present invention, and taken substantially as indicated by the line l-l of Fig. 2; and

V Fig. 2 is a bottom plan view of the spark plug illustrated in Fig. 1.

In approaching the subject of the present ap- I sufficiently short length to insure proper starting and cold-motor performance, there being no provision, however, for increasing the gap as the motor warms up to provide a longer spark found to be more effective under hot motor conditions, which exist at higher speeds and under higher compression.

As illustrated in the acompanying drawing, the present invention comprises a shell indicated, as a whole, by the numeral 3, and mounted therein is a core indicated, as a'whole, by the numeral t formed of suitable insulating material such, for example, as porcelain or the like, the core t being secured in position within the shell 3 by means of a gland 5 screw threaded into a portion of the shell, as indicated at 6.

In the type of plug shown in the drawing, the shell 3 is provided with an elongated chamber 1 having cylindrical side Walls 8 inclined toward each other and terminating adjacent their lower ends in a relatively thin transverse wall portion 9 having an opening I l formed therein, preferably, of substantially less diameter than the diameter of the chamber 1 to provide a restricted opening communicating with the interior of the chamber adjacent the end of the plug, it being understood that in the type of plug shown, and under normal operating conditions, a charge of combustible mixture in the chamber 1 is ignited, thereby projecting a constricted jet of flame through the opening II for igniting the main charge of combustible mixture in the combustion chamber of the engine.

It will be observed by reference to Fig. 1 that the lower end portion l2 of the core t extends a substantial distance into the chamber 1 toward the opening H, and mounted within the core, is a central electrode l3 adapted to extend beyond the end portion .12 of the core, through a portion of the chamber 1 and preferably, into or through a portion of the opening H at the end, of the shell 3.

Mounted on the shell 3, preferably, on'the lower end portion thereof and adapted to extend across a substantial portion of the end wall 9 is a ground electrode indicated, as a whole, by the numeral I4, provided with an inwardly extending. portion l5 positioned within the opening II and extending a substantial distance into the chamber 1 to adjacent the inner end portion l2 of the core 4, and into overlapping relationship with the central electrode 13, the portion I5 of the ground electrode I 4 being inclined with respect to the central electrode l3 in a manner to position the adjacent side portions of the respective electrodes in inclined relation with respect to each other to provide a tapered spark gap within said chamber 7, the said gap having its narrowest portion adjacent or within the opening I I, and its widest portion adjacent the end I2 of the core 6. By such an arrangement, it will be observed that the narrowest portion of the gap is positioned adjacent the end of the shell to provide a gap of sufliciently short width closely adjacent the combustion chamber of the engine to provide a suitable spark for idling speeds and to facilitate easy starting of a cold motor.

When a motor is cold, there is practically no diiference in the temperature and density. of the mixture throughout the levels occurring between the lower end and the upper end of the spark gap formed between the electrodes I3 and portion I5 of the ground electrode, and under such conditions, the spark occurs at the shorter distance across the lower end of the gap adjacent the top of the compression or combustion chamber of the cylinder, so that direct exposure of the spark to the mixture in the compression chamber is assured to provide greater certainty of maximum efiiciency in starting, and under cold-motor conditions, thus, it will be apparent that, for the purpose of reducing resistance and insuring a competent, efficient spark, the spark gap under cold motor conditions should be comparatively short.

As the motor temperatures increase, however, and the plug becomes hot, as when the motor is operating under conditions of higher speeds, a wider spark gap for providing a longer spark is desirable, and under such conditions, the porcelain, for example, adjacent the lower end of the core 3 and the chamber 1 becomes more heated, and the mixture within the chamber I, particularly adjacent the core, becomes rarified as compared with the relatively cooler mixture at the ceiling or top of the combustion chamber, thus, comparatively, reducing the resistance to the passage of a spark between the electrodes adjacent the core and causing the spark to move to a higher level within the chamber I or closer to a point adjacent the upper end of the portion I5 of the ground electrode It. It will be observed that the rarification of the mixture produced adjacent the heated portion I2 of the core 4, and adjacent the widest portion of the spark gap, provides an area of low resistance adjacent the upper inner end of' the portion I5 and provides a longer spark well within the chamber I to insure complete combustion of the mixture therein, particularly when the engine is operating at high speeds and at high temperatures.

In other words, it will be readily understood from the conventional constructions of internal combustion engines and conventional methods of operating such engines, that when the piston approaches that end of the cylinder which carries the spark plug in the act of compressing an explosive charge, the interval of time between the beginning of such stroke and the instant at which said spark occurs is extremely short except when said engine is being actuated slowly by the starter or is operating at relatively low speed before attaining relatively high speed. Due to the relative shortness of this interval when the motor is operating at high speeds, and to the constricted opening II in the end of the plug.

there is not then sufficient time for the charge .of fuel to fully equalize its compression as between the cylinder proper and the chamber of the Bidwell plug. It is apparent therefore, that this high speed condition produces at the instant of the spark, at points well within the chamber of the Bidwell plug, a lower compression of fuel than is produced adjacent the cylinder and adjacent the open end of said chamber. Thus the gas between the inner end of the electrode I5 and that portion of electrode I3 which is transversely opposed thereto is of less density than the gas between the outer end of electrode I3 and that portion of the electrode l5 which is transversely opposed thereto. It is thus seen that this compression difierential cooperates with the temperature differential, elsewhere herein referred to, to produce at the wider portion of said tapered spark gap a more rarifled gasand therefore less resistance to the spark than under conditions existing coincidentally at the shorter portion of said gap.

' Thus the spark occurs adjacent the opening of the chamber when starting and when operating at relatively low speed and when the motor temperature is relatively lowand occurs substantially within said chamber when operating at relatively high speed and when the motor temperature is relatively high-the terms motor and engine as used herein being synonymous.

An arrangement of the character described, which has been found to be very efflcient and desirable is one wherein the spark gap adjacent the lower end of the central electrode I3 is approximately .030 of an inch, the adjacent side portions of the respective electrodes diverging inwardly of the chamber or toward the end of the insulating core to provide a gap adjacent the upper or inner end of the portion I5 of approximately .037 of an inch, it being understood, however, that these dimensions are merely relative and illustrative, and that the dimensions may be varied to suit conditions under which the improved spark plug is employed.

It will be observed from the foregoing description that a suitable gap of reduced dimensions is provided adjacent the opening in the lower end of the plug to insure efiicient starting of a cold motor, and that as the temperature increases the spark moves upwardly along adjacent side portions of the electrodes in accordance with the operating conditions of the engine, this upward movement being induced by the greater rarification and lower resistance of the mixture adjacent the end portion I2 of the core I, the spark being maintained at the higher level in the chamber I under hot motor conditions due to the relative difference in temperatures at the opening II and at the upper or innerend of the portion I5, the relatively cool incoming mixture entering the combustion chamber of the engine tending to maintain a lower temperature adjacent the opening II, while the heat retained in the chamber 1, and particularly by and adjacent the lower end portion I2 of the core 4, serves to maintain a relatively higher temperature adjacent the upper end of the portion I5 or at the wider gap between the electrodes, thereby producing a most emcient spark well within the chamber I to insure eflicient combustion of the charge therein and, by reason of the jet of flame therefrom, insuring more complete ignition of the charge within the combustion chamber of the engine.

It will be observed also, that by reason of the shifting of the spark longitudinally of the electrodes, no one portion of the respective electrodes is subjected to a burning away action caused by continuous sparking heats at one point only, as in conventional types of plugs and, as a consequence, whatever burning away of the electrodes, as may occur, is distributed throughout isease the length of the electrodes over which the spark automatically shifts, so that the rate of reduction of the cross section of the respective electrodes is materially reduced, and necessity for frequent adjusting of the spark gap is thereby avoided, thus materially increasing the life or length of service of a plug embodying features of the present invention, and by reason of the scavenging action of the plug in projecting a jet of flame from the chamber 1, the necessity of frequent cleaning of the plug is obviated.

Obviously, the present invention is not limited to the precise construction and arrangement shown and described; as the same maybe variously modified without departing from the spirit and scope :of the invention as set forth in the appended claims.

What I claim as new Letters Patent is:

1. A spark plug comprising a shell having a chamber formed therein adjacent one end thereof and having an opening communicating with said chamber, an insulating core mounted in said shell, an electrode mounted in said core and extending beyond the end thereof and into said chamber, and a second free-ended electrode mounted on said shell and having its free end and desire to secureby extending into said chamber toward said core and into overlapping unilateral spaced relationship with said first-mentioned electrode, adjacent portions of the respective electrodes being inclined within said chamber with respect to each other and diverging toward said core.

2. A spark plug comprising a shell having a chamber formed therein adjacent one end portion thereof and having a constricted opening in said end portion communicating with said chamber, an insulating core mounted in said shell, a wire-like electrode mounted in said core and extending beyond the end thereof to adjacent said opening, and a second wire-litre electrode mounted on said shell and having a free and extending into said chamber toward said core and into overlapping spark-gap relationship with said first-mentioned electrode, adjacent portions of the respective electrodes being inclined with respect to each other and diverging from adjacent said opening toward said core.

3. A spark plug comprising a shell having a chamber formed therein adjacent one end portion thereof and having an opening in said end portion communicating with said chamber, an

' insulating core mounted in said shell, an electrode mounted in said core and extending beyond the end thereof through a portion of saidcham= her to adjacent said opening, and a second elec-. trode mounted on said shell adjoining said opening and extending through said opening and into said chamber and into overlapping relationship in said chamber with said first-mentioned electrode, adjacent portions oi the respective electrodes being inclined with respect to each other and diverging within said chamber irom adja cent said opening toward said core.

l. A spark plug comprising a shell having a chamber formed therein adjacent one end portion thereof and having an opening in said end portion communicating with said chamber, an insulating core mounted in said shell and extending into said chamber, a wire-like electrode mounted in said core and extending beyond the end thereof through a portion of said chamber and substantially coaxially therewith to adjacent said opening, and a second wire lilre electrode mounted externally of the end portion of said shell and extending through said opening into said chamber and into unilateral overlapping non-parallel spaced spark gap relationship within said chamber with said first-mentioned electrode, adjacent side portions of the respective electrodes being inclined with respect to each other and diverging from adjacent said opening toward said core and the interior of said chamber. a

5. A spark plug comprising a shell having a chamber formed therein adjacent one end portion thereof and having an opening in said end portion of less diameter than the diameter of said chamber and communicating therewith, an insulating core mounted in said shell and extending a substantial distance into said chamber in spaced relation to the side walls thereof, an electrode mounted in said core and extending beyond the end thereof through a portion of said chamber and into said opening, and asecond electrode having one end mounted on the end portion of said shell and its free end extending through said opening into said chamber into a free position adjacent said core and into operative spark gap relationship with said first-mentioned electrode, adjacent side portions of the respective electrodes being inclined with respect to each other and diverging from within said opening toward said core and the interior of said chamber.

6nd sparlsplug comprising a shell having a chamber formed therein, said shell having a transverse wall portion adjacent one of its ends providing an end wall for said chamber, said end wall having an opening therein of substantially less diameter than the. diameter of said chamber. an insulating core mounted in said shell and extending a substantial distance into said chamber, a central electrode mounted in said core and extending beyond the end thereof to adjacent said opening. and a ground electrode mounted on said shell and extending into said chamber to adjacent said core and in overlapping relationship with said central electrode, adjacent side portions of the respective electrodes being inclined with respect to each other and providing a tapered spark gap within said chamber, said gap having its narrowest portion adjacent said opening and its widest portion ad jacent said core.

7. A sparlr plug comprising a shell having an elongated chamber formed therein, said shell having a relatively thin transverse wall portion ad= jacent one of its ends providing an end wall for said chamber, said end wall having an opening therein of substantially less diameter thanthe diameter of said chamber, an insulating core mounted in said shell and extending a substantial distance into said chamber, a central electrode mounted in said core and extending beyond the end thereof and into said opening, and a ground electrode mounted on said wall and extending from said wall into said chamber to adjacent the inner end of said core and in overlapping relationship with saidcentral electrode, adjacent side portions of the respective electrodes being inclined with respect to each other to provide therebetween a tapered spark gap within said chamber, said gap having it nar w st p0r= tion adjacent said opening and its widest portion adjacent said core.

i her, said end wall having an ope ningtherein of substantially less diameter than the diameter of said chamber, an insulating core mounted in said shell and extending a substantial distance into said chamber, a central electrode mounted in said core and extending beyond the end thereof and into said opening, and. a substantially L- shaped ground electrode having one of its legs .mounted on the end portion of said shell and extending across a substantial portion of said end wall and having its other leg extending freely into said chamber to adjacent the inner end of said core and in overlapping spaced relationship with said central electrode, adjacent side portions of the respective electrodes being inclined with respect to each other to provide a tapered spark gap within said chamber, said gap having its narrowest portion adjacent said opening and its widest portion adjacent said inner end of the core.

9. A spark plug comprising a shell having a chamber formed therein andproviding side walls for said chamber, the inner surface of said side walls being inclined toward each other and terminating at their lower ends in a transverse wall portion adjacent one end of said shell and providing an end wall for said chamber of substantially lesser thickness than the thickness of said side walls, said endwall having an opening therein of substantially less diameter than the diameter of said chamber, an insulating core mounted in said shell and extending a substantial distance into said chamber, a central electrode mounted in said core and extending beyond the end thereof to adjacent said opening, and a substantially L-shaped ground electrode having one of its legs mounted externally on the end portion of said shell and extending across a substantial portion of said end-wall andhaving the other of its legs extending freely into said chamber to adjacent the inner end of said core and in overlapping spaced relationship with said central electrode, adjacent side portions of the respective electrodes being inclined with respect to each other to provide a tapered spark gap positioned in part within said chamber, said gap having its narrowest portion adjacent said opening and its widest portion' within said chamber and adjacent said core.

10. In a spark plug of the kind described and in combination, a shell having a chamber formed adjacent one end thereof and provided with a wall forming the end wall of said chamber, said wall having an opening through the same of a diameter substantially less than the diameter of said chamber, a core of insulating material, mounted in the shell and projecting into the chamber, an electrode extending through said core and projecting into the chamber to adjacent the opening in said end wall, a second electrode mounted on the shell and having its free end projecting into said chamber toward the inner end of said core, the axis of said second electrode diverging from the axis of said first 1 1. In a spark plug of the kind described and in combination, a shell provided with a chamher at the inner end thereof, the end of the shell constituting an end wall of the chamber and provided with an opening through the same, a core of insulating material mounted in said shell with a portion of said core constituting a I,

portion of the inner wall of said chamber, an insulated electrode carried by said core and projecting into said chamber with its free end positioned adjacent said opening, a second electrode mounted on said shell and having a portion intermediate its ends positioned adjacent the free' .end of said insulated electrode and projecting inwardly with the free end of said second electrode positioned-adjacent the core end and spaced a greater distance from said insulated electrode than the distance between the free end of said insulated electrode and the adjacent intermediate portionof said second electrode to provide a tapered spark gap within said chamber.

12. A spark plug comprising a shell having a recess formed therein adjacent one end thereof and having an opening communicating with said recess, an insulating core mounted in said shell, an electrode mounted in said core and extending beyond the end thereof and into said recess, and a second electrode secured to said shell adjacent said opening and extending into said recess into substantially overlapping spark-gap relationship with said first mentioned electrode, adjacent portions of the respective electrodes being inclined with respect to each other and having their respective axes diverging within said recess toward said core to provide a tapered spark gap, the degree of the taper of said gap being so limited as to provide at the widest portion of said gap less resistance to the spark than the resistance at the narrowest portion of said gap when the difference in gas densities adjacent said respective portions is the greatest difference produced within the range of conditions of engine operations ordinarily practiced in'the use of said plug.

13. A spark plug comprising a shell having a chamber formed therein adjacent one end portion thereof andhaving an opening in said end portion communicating with said chamber, an insulating core mounted in said shell, an electrode mounted in said core and extending beyond the end thereof toward said opening, and a second electrode mounted on said shell adjacent said opening and extending into said chamber into overlapping spark gap relationship with'said first mentioned electrode, the mean axes of the respective electrodes being inclined with respect to each other and diverging from adjacent said opening toward said core to provide within said chamber a tapered spark gap.

14. A spark plug comprising a shell having a chamber formed therein adjacent one end thereof and having an opening communicating with said chamber, an insulating core mounted in said shell, an electrode mounted in said core and extending beyond the end thereof and into said chamber, and a second electrode mounted on said shell and extending into said chamber into operative relationship with said first mentioned electrode, the respective mean axes of adjacent portions of the respective electrodes being inclined with respect to each other and diverging toward said core to provide within said chamber a plurality c t-operative spark paths of varying lengths, one of said paths within said chamber being approximately .007. of an inch longer than sulator secured to said shell and in part constituting a portion of the inner wall of said chambit iii)

arrears ber, an insulated electrode carried by said insulator and projecting into said chamber, inner electrode means carried by said shell and forming in cooperation with said insulated electrode a relatively long spark path having a, predetermined length and having a position within said chamber predetermined with relation to said opening, and means carried by said shell and forming a second spark path having a relatively substantially smaller length .and being positioned relatively substantially nearer to said opening, each of said spark paths being a substantially unidirectional lineal path ending at a predetermined side oi said insulated electrode.

16. In a spark plug and in combination a shell having within one oi! its ends a chamber having a constricted opening communicating therewith, an insulator having a portion secured within said shell, an insulated electrode carried by said insulator and exposed within said chamber, electrode means supported by said shell and co-operatively associated with said insulated electrode to form within said chamber a relatively long spark gap or spark path relatively near said insulator and electrode means carried by said shell and forming in cooperation with said insulated electrode a relatively short spark gap or spark path positioned relatively substantially remote from said long spark path and relatively n'ear said opening, each of saidspark paths being a substantially unidirectional lineal path ending at a relatively predetermined side of said insuiated electrode.

17. In a spark plug and in combination a shell having within one oi its ends a chamber havin an opening communicating therewith, an insulator secured to said shell, said insulator having a, portion thereof extending coaxially into said chamber toward said opening, an insulated electrode carried by said insulator and extending a substantial distance beyond said portion thereof and into said chamber, inner electrode means supported by said shell and operativelyopposed in spaced relation to a portion of said insulated electrode relatively near said insulator to form at a predetermined side of said insulated electrode Bil dil

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and within said chamber a unidirectionalinner spark ,path oi predeterminedlength, electrode means supported by said shell and operatively opposed in spaced relation to a portion oi said insulated electrode relatively remote from said insulator and substantially remote from said in= ner spark path and i'orming a spark path oi relatively shorter length.

it. In a spark plug and in combination a metal shell having within one oi its ends a chamber having an opening having a minimum transverse dimension substantially smaller than the maximum transverse dimension of said chamber measured from inner wall to inner wall of said shell and tree-ended wire-like electrodes having substantial portions thereof spaced away at all sides thereof from each other and from all said other members, said electrodes being cooperatively opposed within said chamber and providing within said chamber a plurality of substantially unidirectional operative spark paths of substantially varying lengths and of varying positions with relation to each other.

19. In a spark plug and in combination a metal shell having within one oi its ends a chamber having an opening having a minimum transverse dimension substantially smaller than the mani= mum transverse dimension of said chamber measured from inner wall to inner wall of said shell and wire-like electrodes cooperatively opposed within said chamber and within a predetermined side thereof and providing within said side of said chamber a plurality of substantially lineal spark paths of substantially varying lengths and oi substantially varying positions with relation to each other, all other sides of said chamber being free of obstructions to the admission and dischargaof gas to and from the innermost portions of said chamber.

'20. In a spark plug and in combination a shell having within one of its ends a chamber having an opening, an insulator secured to said shell, cooperatively opposed electrodes supported respectively by said shell and by said insulator, one

of said electrodes being disposed throughout its 7 length substantially coaxially with said shell, and providing within said chamber and relatively adjacent a predetermined side thereof a relatively long spark path relatively remote from said opening and providing a relatively short spark path positioned a substantial distance away from said long spark path in the direction of said opening.

21. In a spark plug and in combination a shell having a chamber formed within. one of its end, said chamber having an opening adjacent said end, an insulator secured to said shell and constituting a portion of the inner wall of said chamber, an insulated electrode carried by said insulator and projecting into said chamber, a second electrode attached to said shell and projecting into said chamber into substantially overlapping electrically operative unequally spaced unilaterally disposed non-parallel relationship with said insulated electrode, providing a spark gap of varying width within said chamber and between said electrodes, the widest portion oi said spark gap being substantially nearer said insulator than the narrowest portion of said spark gap.

22. In a spark plug and in combination a shell having a chamber formed within one of its ends, said chamber having an opening adjacent said end, an insulator secured to said shell and constituting a portion 01 the inner wall of said chamber, an insulated electrode carried by said insulator and projecting into said chamber, electrode means carried by said shell and forming in cooperation with said insulated electrode a substantially unidirectional inner spark path oi a predetermined lineal dimension and having a predetermined position within said chamber and extending from adjacent said insulator toward a predetermined side of said chamber and electrode means forming in cooperation with said insulated electrode a second spark path having a relatively smaller dimension and being positioned a substantial distance away from said inner spark path, in the direction oi said opening.

23. The method of igniting fuel in a cylinder oi an internal combustion engine and in a chamber of a spark plug operatively related thereto having an opening communicating with said cyiin= der, which method. consists oi admitting a portion of each charge of explosive gas from the cylinder into said chamber and producing a sparlr across a gap adjacent said opening when start= ing said engine and while said engine is relatively low in temperature and is operating at rel. tively low speed and under relatively low load, and thereafter producing a spark throughout a path maintained substantially at a predetermined position substantially within said chamber and relatively substantially remote from said opening and cylinder when said engine is relatively high in temperature and is operating at relatively high speed and under relatively high load.

24. The method of igniting fuel in a cylinder of an internal combustion engine and in a chamber of a spark plug operatively related thereto and having a constrictedjopening communicating with said cylinder, which-methodconsists of admitting a portion of each charge of explosive gas from the cylinder into said chamber and producing a spark across a gap adjacent said -of an internal combustion engine and in a chamber of a spark plug operatively related thereto and having an opening communicating with said cylinder, which method consists of admitting a portion of each charge of explosive gas from the cylinder into said chamber and producing a spark across a gap adjacent said opening when starting said engine and while said engine is relatively low in temperature and is operating at relatively low speed and under relatively low load, and thereafter producing a'relativcly longer spark throughout a path ofv predetermined length and of predeterminedposition within said chamber and relatively substantially remote from said opening and cylinder when said engine is relatively high in temperature and is operating at relatively high speed and under relatively igh load, and of'causing said charge of gas in said cylinder under said relatively high conditions to be ignited by an advance of flame through said opening and into said cylinder.

26. The method of igniting fuel in the cylinder of an internal combustion engine and in a chamber of a spark plug operatively related thereto and having a constricted opening communicating with said cylinder, which method consists of operating conditions.

admitting a-portion of each charge of explosive gas from the cylinder into said chamber and of producing a spark across a gap adjacent said opening when starting the said engine and while said engine is relatively low in temperature andv is operating at relatively low speed and under relatively low load, and thereafter producing a relatively'longer spark throughout a path of predeterminedlength and of predetermined position within said chamber and remote from the inner.

walls of said chamber and relatively substantially remote from said opening and cylinder when said engine is relatively high in temperature and is operating at relatively high speed and under relatively high load, and of causing said charge of; gas in said cylinder under said relatively high conditions to be ignited by an advance of flame through said opening and into said cylinder.

27. A method of energizing an internal combustion gasoline engine of conventional type hav-;

ing a fuel compression cylinder, said method consisting of compressing within said cylinder successive charges of explosive gas and of admitting, into a chamber adjacent said cylinder and communicating therewith through an opening there.

between, a portion of each such charge and of igniting such charge by producinga spark at one or anotherof two predetermined positions. one of said positions being substantially remote from said opening and substantially within said chamber and the other of said positions being substantially remote from said one position and spaced therefrom in the direction of said cylinder, and of producing said spark selectively at one or another of said positions and in timing with the: compression of an individual such charge and according to the value of coincidental differentials in the density of said gas at said respective positions.

28. In a spark plug of the kind described and.

in combination, a shell having within one of its ends a chamber having an opening communicating therewith, electrodes supported by said shell from each other, one of said pathsrbeing positioned within said chamber, said spark paths being automatically alternately operative selectively according to diiferentials in respectively 'adjacent EARL E. BIDWELL.

' and positioned to form a plurality of electrically parallel spark paths spaced a substantial distance.-

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