Antechamber type spark plug
US 2642054 A
Description (OCR text may contain errors)
June 16, 1953 G, F, vwRlGl-rr 2,642,054
ANTECHAMBER TYPE SPARK PLUG MECHANISM Filed May 20, 1950 lull:l
INVENToR. G/LL-er F. wR/GHT A T TOENE'YS Patented June 16, 1953 UNITED srs lANTECI-IABIBER TYPE SPARK7 Pl'iUGrr MECHANISM corporation of Delaware Application May 20, 1950, Serial No. 163,155`
(cl. 12s-169) l Claims.
This invention relates to. spark plug nfiechanismy of the type intended for application to an internal combustion engine, and which forms an antechamber with respect. to the engines combustion space. f
Many spark plugs andv spark plugv adaptors have been proposed heretof'oreof special design, intended to reduce the tendency ofthe spark plug to become` fouled by"y the deposit of carbon and lead compounds from. gasoline, as Well as to re,- duce d'etonation, increase power; and generally to improve combustion eihciency.v Some of these proposed. designs have been more efiective than others. Thev spark plug mechanism according to. the present invention has proven to be particularly tree from fouling or burning of the. electrodes or short circuiting caused by deposit of carbon or lead compounds on theA spark plug insulator and in its cavity. The engine operation temperature limit at which preignition Will occur is greatly increased, yet the combustion is propagated through the combustible mixture in the engines combustion space so effectively by the spark plug mechanism that an increase in power and engine efciency is obtained whilel detonatio-n is decreased'. As a result of the more elective flame propagation, the engine can be started more easily and idles smoothly at lower speeds.
The spark plug mechanism of this invention is applicable to an internal combustion engine by being screwed into Ythe usual spark plugA hole,A so that it does not reduire any modification of existing engines, although it may be built to t various sizes of hole. Its structure, however,
provides: an antechamber With-in which the electrodes formi-ng. the-spark gap are housed. .The
l designation spark plug mechanism in this specification is intended tol include.. both an. arangeinent in which the antechamber is formed in an adaptor to be screwed into the engine and into which a standard spark plug may be screwed., and also a spark plug which is itself specially formed in accordance with the invention.
In order to'accomplishthe advantages enumerated above it has :been found that, within limits, the antechamber must have a certain shape, proportions and dimensions, and the elec.- trodes forming the spark gap must be located in ratherA a particular position in the antecharnber. Maximum eiectiveness of the spark plug operation depends largely on a. proper relation between various characteristics of the spark plug mechanism, and a nice balance of proportions and dimensions must be maintained between the parts of the spark plug mechanism,
More specifically. for maximum power andy elo.-Y sence ot detonetion and preienition. the entechamber Within the spark plugy mechanism is convergent toward the inner end of the spark p11-1g, which is theend to be exposed within the engine.. combustion ehember. and opens et.. such end through an. aperture which must be sufficiently 'smallv as to,r produce the desired nozzle effect. of gas 4mov-ing into andout of the antechamber,v yet, not so small as torestrict excessively the.l passage of such gas or cause excessive veloc`- ities in the aperture.. electrodesformingthe spark gap must be looated suiiioiently fer trom the inner end. of the Spark plus and therestrioted opening. of'fthe anteohamber es to be removed trom direc-tooritaot with rich. combustible misture. to reduce the tendency for omzbori end. leed eorrirmmiy deposits. to form.. and preferably the space behind the. electrodes is. smell'and, protested by e. shoulder or step. formation between. it and. themein portion of. the. aneohamper.
Spark. plus, meohariisms met be. classified as either of the hot type.. where heet cannot. be. 'trans-v mitted too readily from the metal and ceramic lnsulating material of the central electrode and core to the shell of the spark plug mechanism, or of the cold type Where the metal and insulating material of thecentral electrode is in quite direct contact with the shell of the spark plugy mechanism,l so that heat will be dissipated readily from the core. The spark plug mechanism of this invention has the unique advantage of permitting avery cold type of construction Without the usual tendency toward excessive fouling.
Additionally, certain parts of the spark plug mechanismare shaped to be more eiective. Thus the restricted opening from the antechamber through the innery end of the spark plug'v mechamism is rounded. Haringfrom the minimum open-v ingr to the inner end of the spark plug to promote smoothness of flow of. the ses and minimum turbulence both when moving; from the combustion space into they antechamber and when moving fromtheantechamber intofthe combustion space. Preferably also the antechamber converges toward the restricted opening and is faired into its wall.. and such `ooriverserloe is termed by ooncavoli'. eurveci Wells of. the. mit.eohamloe.i2l all thesefeatur'esVY contribute to the effectiveness of the sparkplug.
Critical dimensions and proportionsoi the spark. plus meohem'sm will be pointedout inthefol-` lowing det led desorinton of 'representative forms. shown in the accompanying drawings- Figure. l. is a longitudinal sectional view through v a sparky plus constructed in aooordanoe'with the f internal combustion engine and incorporates anY antechamber. The spark plug body includes a shell I having an externally threaded inner end portion I!) of a standard size to s-crew into the usual port or spark plug hole of an internal combustion engine. The external diameter of the thread on this part may, for example, be eighteen millimeters. At the outer end of this threaded portion is an external shoulder I l, and slightly farther from the inner end I6 of the spark plug7 that is the end adapted to be exposed within the engines` combustion space, is an internal shoulder I2. Near the outer end of the shell l is a noncircular portion |3, preferably hexagonal, to which a wrench may be applied for screwing the threaded portion I8 into an engine port or for unscrewing the plug from the engine port.
Within the shell I is received a bushing 3,
completing the plug body, having a step approximately midway between its ends which bears against the internal shoulder I2 of the shell. The shell may have a further slight shoulder I4 against which the inner end of bushing 2 seats, such inner bushing end being located at least substantially as close to the inner end I6 of the plug body as the outer end of the threaded portion I Il. Preferably this bushing is metal and its axially inner end carries the grounded electrode 2| located immediately adjacent to the inner end face of the bushing.
The central electrode 3 is mounted in a ceramic spindle carrying a metal band 3| threaded externally to mesh with internal threads formed in the outer end of the shell I. A spacing washer 4 is interposed between the band 3| and the outer end of bushing 2, which is of selected thickness to establish the proper width of the spark gap between the grounded electrode 2| and the central electrode 3. The outer end of the band 3| has a suitable formation 32 to receive a wrench operable to rotate the spindle 30 relative to the shell.
The outer end of the shell I is closed by a cap 5 having an externally threaded inner end complemental to the internal thread of the shell. Outwardly of this threaded end portion the sleeve has av noncircular wrench-engaging part 5!! which preferably is hexagonal. This cap has a ceramic lining 5|, insulating the cap and shell from the terminal 33 on the outer end ofthe spindle 32|. The outer end of `the cap is open for reception of an electrical conductor to engage the terminal 33, and preferably has external threads 52 to receive a protective cap or for securement vof an ignition wire shield. Y
Of the parts described above the spindle 3G, central electrode 3 and terminal 33, and the cap 5, may be conventional. The invention of the present spark plugv mechanism resides in the antechamber formation within the spark plug bodycomposed of the shell I and bushing 2, and
the relationship of the electrodes. 3 and 2l. and
these two portions.
the inner end of spindle 3G relative to such antechamber.
The formation of the antechamber within the inner end portion of the body includes a large portion and a restricted opening through the inner end I'B of shell l, such opening aifording communication between the large portion of the antechamber and the combustion space of the internal combustion engine. The inner walls of such large antechamber portion converge from a maximum diameter or cross sectional zone I5 toward a minimum diameter or cross sectional portion in the restricted opening. Such convergent walls preferably are concave and are reasonably faired into the restricted orice or minimum cross sectional portion to promote smooth flow of gas in either direction between While neither the degree nor curvature of the antechamber wall is critical, such curvature may conveniently be of circular arcuate shape, a diameter of the maximum cross sectional portion of the antechamber substantially coinciding with a radius of such circular arc, and the radius of such arc preferably being of a length approximately three times as great as the radius of the maximum cross-sectional portion of the antechamber, as shown in Figures 1 and 3. Preferably the antechamber is of circular cross section, but it may be noncircular, in which case the word diameter as used in this description will be understood to indicate the transverse width of the antechamber. Additionally, the orice flares from its minimum cross sectional portion toward the inner end I6 of the spark plug, preferably in a smooth curve, again to reduce the turbulence of flow from the engines combustion space into the orifice or from the antechamber through the orice into the engines combustion space. Such construction eliminates sharp corners which otherwise might be heated to incandescence and cause preignition.
Immediately at the side of the large portion of the antechamber away from the inner end I5 of the spark plug body the axially inner end of bushing 2 forms a radially inwardly projecting shoulder in the antechamber. The electrodes 2| and 3 are located substantially at such shoulder, Fig. 3 showing the gap coplanar with such shoulder and Figs. 1 and 4 showing the gap immediately at the side of such shoulder away from the orifice and body end I6, that is axially outward from such shoulder, and within a reduced bore portion 22 of the bushing.
The inner end of the insulating spindle 3i] is tapered inwardly, and in order to provide sufcient clearance between the bushing 2 and spindle the bore of the bushing has an enlarged portion 23 toward its axially outer end, i. e. the bore portion 22 at the inner end of such bushing is stepped radially inward toward the spindle porcelain to reduce the space around its inner end. lThe lengths and diameters of the parts of this stepped bore should be related to the lengths and diameters of corresponding portions of the inner end of spindle 30 so that sufficient clearance will be left between the two at all locations axially of them to accommodate some deposit Vof carbon and lead compounds Afrom the fuel, while this space is narrow enough to keep the portion of the antechamber outwardly of the spark gap of small volume as compared to the volume of the antechamber inwardly from the spark gap.
If the inner end orice of the antechamber is `too restricted' fori the." size of the iante'chamber as a whore, thezld'esired functioning 'of the sparkv gasto ilow from the engine combustion space into the antechamber and out again. On vthe "other hand, if the minimum diameter of vsuch vorifice' IT is more than about threefeighths; of
'an inch, the desired nozzle effect would not be secured and excessive fouling caused by deposit Y of carbon and leadv compounds in the' antecham* ber would occur. v
The maximum diameter of the large portion of the antechamber l5 may be. from seven-.six-rteenths of an inch to nine-sixteenths of an inch, an appreciable reduction below the former Value increasing the tendency for carbon and lead compounds to be deposited in the antechamber, and any appreciable increase above the latter dimension causing excessive reduction in the power produced by the engine. The'curved surfaces !3 may be of -circulararcuate shape having a radius Vof approximately threeefourths of an inch and centers in the vplane dened by the shoulder formed by the inner end o'f bushing 2. ,f
In such a spark plug it will be seen that the `minimum orifice diameter is between one-third and two-thirds of the diameter of the maximum cross section of the antechamber.
InV an IB millimeter spark plughaving a re.- A.
stricted orice minimum diameter of one-fourth inch and one-half inch as a maximum diameter Y or the antechamber, the total# volume of the antechamber progressively tapered in'cross section toward such orifice with walls orv circular q.
arcuate curvature as described `above was @.0975 cubic inch and the area of the restricted oriiice (1.049 square inch. This gives a volume to area ratio of approximately two, where the volume of the antechamber is in terms of cubic inches and the minimum cross section of the restricted oririce is given in square inches. A ratio of volume to area of this order has resulted in an excellent Spark plus mechanism, Whereas if the volume of the-antechamber is increased substantially without an increase in the sizeof orinca. some loss. in engine power occurs, and at hishpewer excessive heating. may cause preignition; ,Olathe other handii the .volume oi the antechamber is reduced .substantially below `this ratio without ing them to burn off ccmparativelyquickly,` and the antechamfber. will tend to become iouled by deposit of carbon and lead compounds.
Eiciency of the spark plug is prejudiced by making the orice l'iat the inner end of the the. electrodes must be remote from the restricted orice of the antechamber at the inner-'end of the spark plug and substantially at the inwardly projecting shoulder of the antechamber,
change in. minimum area of; the orifice the elec- .trodes will be exposed to excessive heatl caus antechamber either too small ,or too long. Preff erably the aperture ares in both directions from the minimum diameter section.v In addition for at least sixty percent of the length ofthe ante*g chamber between its zone of maximum crossv section l5 and the inner end U5 of thespark plug the diameter of the antechamber should be at least Sixtypercent of .the maximumdiameter, -AlsO the spacing between the orice portion oi minimum cross section and' such shoulder being at least one and one-half times the diameter of such minimum cross-sectional portion.
To reduce the tendency of carbon and lead compounds to be deposited in the space radially outwardly of the spark gap,l which would tend to cause a short'circuit, the volume of that porl tion of the antechamber axially. outwardly of the spark gap should be a minor portion of the volume of the entire antechamber. In fact, the volume of that portion of the antechamberax+ ially outwardly of the Zone of maximum cross section of the antechamber should be a minor portion of the volume of the entire antechamber, Conversely, of course, that portion of the antechamber between the zone of maximum cross section and the inner end i6 of the spark plug has a volume which is a major portion of the entire volume of the antecharnber. In a spark plug of this type it is also preferred that' the grounded electrode 2| project radially into a position overlapping the central electrode, as shown in Figures 1 and 4. It is possible, however, to employ electrodes of other types,.such, forvexample, as that shown in Figure 3, because of the noncritical location of the electrodes, so long as they are remote from the aperture H and at or adjacent to the inwardly projecting shoulder of the antechamber.
Features of the spark plug shown in Figure 1 may be incorporated in an adaptor and spark plug combination, as shown in Figure 3. In this structure the proportions and dimensions of the antechamber from its portion of maximum cross section l5 toward its inner end I6 are all the same as in Figure. l,A and are numbered correspondingly. Theshoulder I4' of the adaptor shell may be a little wider than the corresponding shoulder in Figure l, and the bore of the shell is threaded internally from its outer end down to this shoulder to receive the complementally threaded inner end of the shell E of a conventional spark plug. The inner end of such spark plug shell then forms the shoulder corresponding to the shoulder formed by the inner end of bushing 2 inthe spark plug of Figure l, and the adaptor shell and spark plug shell together-form the body of the spark plug mechanism. Instead oi the wall ofthe adaptor shell l being as long as the shell l in Figure 1, its entire portion I3 outwardly of its inner threaded end portion Ill, which extends from the inner end of the adaptor body to allocation beyondthe shoulder I4 and the inner end of thespark plug, may be of nonc-ircular shape, such as hexagonal, to receive a wrench for inserting or removing the adaptor. The spark plug shell also may have a nonci-i'cular portion 60', such as of hexagonal shape, which can bey gripped by a wrench for assembly of the spark' plug and adaptor.
The, central electrode 3, its spindle til, boss Sli, gasket 3.5 and retaining nut 3S threaded into an internal thread of the spark plug shell 6 may all beconventional. Also the complemental shapes .of the inner end of the spindle 30 and the bore of the inner end portion of the spark plug shell 60 maybe conventional. In factV the spark plug `loi Figure 3 may be of a standard type in its entirety, for example a small size, vl millimeter,
spark plug, or, if. the wall thickness. of the 7 adaptor I is increased, a I millimeter sparkplug. In view of the similarity of shape, proportions and dimensions of the various parts of the spark plug and adaptor combination shown in Figure 3 to those of the spark plug shown in Figure 1, detailed description of these features need not be duplicated.
In Figure 4 a modication is shown in which the element forming the shoulder in the antechamber is integral with the shell. In this instance the shell I has the thread I0 on its inner end portion extending from its inner end substantially to the inner end of the antechamber proper at shoulder I4, and the walls I8 of the cavity are curved between the maximum cross-sectional portion l5 and the minimum cross-sectional portion Il of the restricted orifice, as in the form shown in Figure 1. Other parts are numbered correspondingly. The principal difference lies in the shoulder I4 facing axially inward, instead of axially outward like the shoulder I4 of the spark plug in Figure 1. The cavityv 22 is thus formed in the shell itself rather than in a bushing inserted into the sleeve. Also, the nonoircular portion I3, corresponding to the hexagonal portion I3 of Figure l, is closer to the inner end I@ of the spark plug.
The spark plug mechanisms shown in Figures 1 and 3 are nominally of the hot type because of the spacing between the central electrode spindle and encircling spark plug body extending a considerable distance from the endof the spindle tip. In Figure 4 a spark plug of the cold type is shown, in which the end of the insulating spindle 30 radially inwardly of the enlargement 34 is shorter than in the other forms shownl and has a shoulder 31 which bears against a gasket 35 close to the bore 2li. Consequently, there is a shorter path'for heat to be conducted from the core for dissipation through the threaded portion I0 of the spark plug into the engine than in the other types of plug shown, and there is less core surface subjected to the heat of combustion. Outwardly of the enlargement 34 is the retaining nut 36 screwed into internal threads in the shell I" in the same manner that the nut 36 is secured in the Kshell 5 of the spark plug shown in Fig'- ure 3.
Actually the core of the spark plug shown in Figure 1 (may be cooler than the core of a spark plug such as shown in Figure 4 since heat cannot be conducted readily between the bushing 2 and the body I of this spark plug because of the discontinuity of these parts. The threaded engagement between the metal portion 3| of the spark plug core and the body I provides a better heat conducting path than between the bushing and the body, Consequently, heat may flow from the ceramic core in Figure l through the threaded connection between the part 3l and the body I, and down to the threads I0 for dissipation into the engine more readily than heat can ow from the bushing 2 to the body I.` While the inner end of the core spindle 30 will still probably be somewhat hotter than the bushing 2, it will be cooler than if this bushing were formed integral with the spark plug body, and the cooler the core tip the less will be the tendency for preignition to occur. At the same time, because of the long space between the spindle tip and bushing, the less chance is there for fouling and shorting out of the plug, despite accumulation of lead and carbon in this space. By keeping such space around the core tip, the less unburned fuel can penetrate into this space from which carbon and lead can be deposited. This construction, therefore,` reduces fouling to a minimum without corresponding increase'in the-tendency for preignition to occur, which normally would result from the use of a hot type spark plug construction in such a situation.
The precise action in operation of the spark plug mechanism described is not known, although the general results of a minimum accumulation of fouling deposits of carbon and lead compounds in theantechamber even during operation at high speeds overextended periods, increased power, reduced detonation, easier starting, smoother and longer idling, and more eilicient fuel combustion than obtained with other types of spark plugs, have been ascertained by tests. It is believed that during compression combustible mixture flowing from the engine through the restricted orifice into the enlarged portion of the antechamber will remain in a stratum rather definitely segregated from a stratum of burned mixture in the vicinity of the electrodes, Consequently the electrode vicinity will be comparatively free from liquid or gaseous materials from which carbon or lead compounds may be precipitated onto the walls of the antechamber, The amount of combustible mixture actually entering the antechamber will depend somewhat on the capacity and compression ratio of the engines combustion chamber.
Even at completion of the compression stroke, presumably because of the absence of appreciable turbulence in the antechamber, the combustible mixture will be very lean in the enlarged portion of the antechamber, and may be progressively leaner from the restricted orice toward the electrodes. Adajcent to the electrodes the mixture need only be sufficiently concentrated to ignite and initiate the burning of the mixture in the antechamber, for projection of aiame into the engines combustion space. Any deposit of carbon and lead compounds on the walls of the antechamber around or axially outwardly of the electrodes is consequently very small, but after extendeduse of the spark plug some deposit occurs in the portion of the antechamber between the electrodes and the spark plugs inner end. Such deposit is found to be graduated axially, being heavier at the inner end of the spark plug and. progressively lighter toward the electrodes, apparently corresponding to the `fuel to air ratio variation axially of the antechamber.
When the mixture within the antechamber is ignited, a tongue of ame will be projected through the restricted orifice into the combustible mixture within the engines combustion space to propagate combustion rapidly and thoroughly throughout such space. Because of the projection of such a tongue of ame into the combustion space, a leaner mixture can be satisfactorily ignited than can be ignited by a spark gap alone. The greater power and efliciency of the engine presumably results from more complete combustion of the mixture.
I claim as my invention:
1. A yspark plug comprising a body having an internal chamber of circular cross section, an internal shoulder in said chamber facing toward the inner end of said body, the walls of said chamber being of circular arcuate shape in an axial direction and converging from said internal shoulder toward the inner end of the said body, the radius of curvature of said Walls being approximately three times the maximum radius of said chamber, and the centers of curvature oi axial wall elements being substantially in the plane of said internal shoulder, said body having an opening from said internal chamber through the bodys inner end, an insulator supporting a first electrode within said body and disposed adjacent to said internal shoulder, a second 'electrode electrically connected to -said body, cooperating with said rst electrode and disposed adjacent to said internal shoulder, and an external shoulder on said body facing toward the inner end of said body and spaced therefrom a distance at least substantially as great as the distance between said internal shoulder and the inner end of said body, and said body being externally threaded from its inner end substantially to said external shoulder for reception in the spark plug port of an engine.
2. A spark plug comprising a body having an internal chamber, an internal shoulder within said chamber facing toward the inner end of said body, said internal chamber flaring away from the inner end of said body and having an opening through the bodys inner end of a minimum Width greater than its axial extent from the inner end of the body to the flaring chamber, an insulator supporting a rst electrode Within said body and disposed adjacent to said internal shoulder, and a second electrode electrically connected to said body, cooperating with said rst electrode and disposed adjacent to said internal shoulder, said body and said insulator being spaced apart and thereby forming therebetween an annular space at the side of said internal shoulder remote from the inner end of said body of an axial extent at least substantially as great as the distance between said internal shoulder and the inner end of said body.
3. A spark plug comprising a body having an internal chamber, an internal shoulder within said chamber facing toward the inner end of said body, said body having an opening from said internal chamber through the bodys inner end of a minimum area between one-ninth and onehalf of the maximum cross-sectional area of said internal chamber, an insulator disposed centrally Within said body supporting a first electrode within said body and disposed adjacent to said internal shoulder, and a second electrode electrically connected to said body, cooperating with said rst electrode and disposed adjacent to said internal shoulder, said body and said insulator being spaced apart and thereby forming a narrow annular portion of said internal chamber of an axial extent at the side of said internal shoulder remote from the inner end of said body at least substantially as great as the distance between said internal shoulder and the inner end of said body and of a volume a minor portionof the total volume of said internal chamber, and an external shoulder on said body facing toward the inner end of said body and spaced therefrom a distance at least substantially as great as the distance between said internal shoulder and the inner end of said body, and said body being externally threaded from its inner end substantially to said external shoulder for reception in the spark plug port of an engine.
4. A spark plug comprising a body having an l@ internal chamber, an internal shoulder Within said chamber facing toward the inner end of said body, said body having an opening from said internal chamber through the bodys inner end of a minimum area between one-ninth and one-half of the maximum cross-sectional area of said internal chamber, an insulator disposed centrally within said body supporting a first electrode within said body and disposed adjacent to said internal shoulder, and a second electrode electrically connected to said body, cooperating with said rst electrode and disposed adjacent to said internal shoulder, said body and said insulator being spaced apart and thereby forming a narrow annular portion of said internal chamber at the side of said internal shoulder remote from the inner end of said body of a volume a minor portion of the total Volume of said internal chamber, the peripheral extent of that portion of said chamber formed by said internal shoulder being less than the peripheral extent of a portion of said chamber more remote from the inner end of said body, and an external shoulder on said body facing toward the inner end of said body and spaced therefrom a distance at least substantially'as great as the distance between said internal shoulder' and the inner end of said body, and said body being externally f threaded froml its inner end substantially to said external shoulder for reception in the spark plug port of an engine.
5. A spark plug comprising a body having an internal chamber, an internal shoulder within said chamber facing toward the inner end of said body, said body having an opening from said internal chamber through the bodys inner end Vof a minimum area between one-ninth and onehalf of the maximum cross-sectional area of said internal chamber, an insulator disposed centrally within said body supporting a rst electrode within said body and disposed adjacent to said internal shoulder, and a second electrode electrically connected to said body, cooperating with said first electrode and disposed adjacent to said internal shoulder, said'body and said insulator being spaced apart and thereby forming a narrow annular portion of said internal chamber at the side of said internal shoulder remote from the inner end of said body of a volume a minor portion of the total volume of said internal chamber, the peripheral extent of that portion of said chamber formed by said internal shoulder being less than the peripheral extent of a portion of said lhiajmber more remote from the inner end of said GILBERT F. WRIGHT.
References Cited in the file of this patent UNITED STATES PATENTS Great Britain Apr. 13, 1937