US2208178A - Spark plug - Google Patents

Description

July 16, 1940. Q BERSTLER 2,208,178

SPARK PLUG Filed April 15, 1939 INVENTOR.

C f/ i BerJf/er BY A TTORNE Y.

Patented July 16, 1940 UNITED STATES PATENT OFFICE SPARK PLUG Reading, Pa.

Application April 15, 1939, Serial No. 267,995

17 Claims.

My invention relates to spark plugs, and particularly to novel means and methods controlling the temperatures and improving the operating characteristics thereof.

In internal combustion engines, the firing of the compressed gas charges has always been a problem, and particularly upon the introduction of modern high-compression engines, diihculty has resulted from the heating of the spark plugs,

more at certain speeds and loads than at others.

With hard driving, the standard plugs soon lose effectiveness to such extent as to materially reduce the power and pickup of a car that, if it were not for this feature, would operate, as it does while it is new, for a much longer period of time.

A great many suggestions have been made for overcoming this objection, including the making of plugsof greatly reduced size, producing them from expensive materials, providing them with cooling fins, and altering them otherwise.

Plugs of standard makes, in regular commercial use, have the common feature of an inner end tip, or nose, projecting toward, or through, the inner end of the shell, in close fitting relation to the center electrode, and spaced radially inwardly from the shell.

These tips become incandescent in use, resulting in fusion and volatization of the metal and dielectric parts, causing excessive combustion inside the plugs, but outside the insulators, and quickly impairing the usefulness of the plugs.

Certain of these, and other, former plugs, in particular service, are too cool, which causes them to quickly build up carbon deposits, and to reduce the intensity of the sparks, or short circuit the spark gaps.

From these facts, for a spark plug to have eflicient operation and long life, it should be neither too hot nor too cool, but should effect a balance between these extremes over a wider range of operating conditions, such as the speed and load, and the construction and operation of the engine in which it is employed.

It should be hot enough to burn, or prevent, carbon deposits, but not substantially hotter than this, and a plug having such operation over a wide range of operating conditions, as does the plug of my invention, may be characterized as the most effectively cool plug.

Another feature common to standard plugs is the corrugated, or ridged, shape of the outer ends of the insulators, ostensibly to provide surface creepage distance, but apparently having little value for this purpose, and being of easier breakage, as well as unsightly.

The metal shells of commercial spark plugs have assumed efiicient standard form, in which various modified porcelain shapes have been tried. However, these so-called porcelains must be constructed to avoid thin sections, sudden changes in section, and other features, whereby they may be assembled under comparatively great pressure, in the metal shells without breakage, or the introduction of minute cracks, fissures, or weakness resulting in early failure of the plugs.

Many other shapes have also been suggested, with the result of apparently nothing better on the market than the plugs of simple standard well-known makes having the aforementioned tips and ridges on the insulators.

An object of this invention is to overcome the above-mentioned difficulties, and to provide a spark plug that will operate more nearly at the critical, or correct, temperature than those heretofore employed and suggested.

Another object of the invention is to provide a spark plug that will increase the horsepower and driving torque, and improve the general operating efficiency of an automotive engine.

Another object of the invention is to prevent the local concentration of excessive heat in a spark plug, as well as the general undue heating of plugs as heretofore constructed, and to provide a plug that will operate at more nearly the critical temperature, which is not hot enough to cause preignition, or to impair the operating efficiency of an engine, or which is not cool enough to cause fouling and failure of the plugs.

Another object of the invention is to provide a pocket space or chamber in the inner end of a spark plug insulator, as distinguished from the inner end of the plug generally, of sufiicient depth and capacity, and of other novel character, to provide for the compression or reception therein of a substantial volume of gas sufficient to provide for the removal of dead air from, and the supply of a good gas mixture at, the arcing zone, and to avoid excessive difierences of temperature between diiferent regions of the pocket space.

Another object of the invention is tocontrol the depth or capacity of pocket spaces of the above-indicated character, in different plugs, in accordance with compression ratio, whereby, as this ratio increases, such capacity is decreased, and, as the ratio decreases the capacity is increased.

Another object of the invention is to reduce the compression and flash volume inside a spark plug, and particularly outside the insulator in the plug.

Another object of the invention is to take advantage, in a spark plug, of the principle that, to have an insulator surface substantially conform to the electrostatic field, will enhance the operation and appearance of the plug, and render it unnecessary to provide surface-creepage ridges of difficult manufacture and ready breakage.

Another object of the invention is to provide spark-plug insulators of the herein indicated character that are as readily adapted for use in standard shells as the former porcelains, and to provide plugs that are as 'well'adapted to standard engines as the former plugs.

Another object of the invention is to provide a spark-plug insulator that is of easy manufacture by existing methods, that is of ready assembly with a shell under great pressure, without undue danger of injury, that is free from delicate or readily-breakable parts for damage in manufacture, handling, shipping or operation, and that will perform its function for a long -period of time. I

Another object of the invention is to providea ground electrode for 'a -'-spark plug that resists travel of the are from the intended arcingzone to the shell on which the electrode is mounted.

Another object of the invention is to provide a method of controlling the temperature and the operating characteris'ticsoi "spark plugs.

A further object of the invention is to :provide a spark plug, of the character herein set "forth, that is-s'imp'l'e and durable in construction, economicalto manufa'cture, and efiective in its operation.

With such objects in 'view, as-well;as other ad vantages whichmay be incident to a utilization of the" improvements, the invention comprises the elements and combinations thereof herein set forth and claimed, with the understanding that the several necessary elements, constituting the same, may be 'varied inproportion, arrangement, texture and other features, without departing fromthespirit and scope of the inventionzas intended, and as set forth in the "drawingpspecification'and claims.

In order to render theinvention more clearly understood, means are shown in"the:accompanying drawing :for carrying the same. into practical efiect, i'without limitingthefinnorovements, :in the useful applications thereof, to the particular constructions-shown and described, which are given merely byway'of example.

In the-drawing:

.Figure .1 is a'viewyon-an enlarged scale, :par- .tiallyiin side elevation and partially in e'longi- .tudinal 'icentral-iplan'e z-section, 20]? a spark plug embodying iparts of the invention Fig. '2 is a view, similar to the lower portion .of ll, of the invention in -.another form, "or stage;

Fig.3 is'a view, similar "to Fig. 2,.ofztheinventionzinanother form;

a4 is a view, similar to :Fig, 3, -'of the "invention in ax-further form; I

Fig. 5 is a contour diagram, in theznatureof a longitudinalcentral-plane templet. or patternot the: lower end "of the plug, :more nearly as shown in Fig.l,*'but. larger; andlhaving imposedthereon certain dotted lines indicating "the above-mentioned tipfeature of former practice; and

Fig. 6 is a similar diagram of portionsof the upper, or outer,'end'length'of the :plug, on'an enlarged" scale, illustrating the I'EIQtiOIl'TOf certain structural v:parts *to the electrostatic field in this region.

In practicing the invention, the longitudinally inner, or firing, end of the plug insulator, instead of projecting toward the combustion chamber, or are zone, as a tip or nose, closely surrounding the center electrode in radially spaced relation to the shell, as in standard practice, is formed as a concavity, like a cup; or pocket, having its "inner longitudinal sides in free-space relation to the inner electrode.

This inner end pocket provides the free space around the electrode for a distance therealong at least sufficient to provide proper surface creepage from the inner electrode to'the shell, or to the ground electrode. The pocket may cause compression of inert gas, or dead air, around the electrode, or otherwise prevent the imposi-- tion of the intense fire of combustion against the bottom and side portions of the cup, or subject these portions to fire or heat only sufficient to maintain these parts clean.

Thesdepth and capacity of .this'cup are suflicient to provide for the compression, .or reception, in the cup .Of .asubstantial volume of gas, and to avoid excessive diiferences of temperature between diiferent regions therein. In other words, in accordance as the compression ratio is large or small, the space depth and volume of the pocket will-be small or large, respectively,"whereby to remove any dead :air from the region .of the arc gap, to provide a proper .gas mixture at this point, to provide sufficient heat at vall parts of the pocket to avoid the formation of carbon, and'to prevent .the inner recesses .of the pocket from becoming suificientlyacool to allow the collection of :carbon deposits.

Other considerations :in the formation of the cup, or pocket, are the cross section, strength,

texture and manufacture thereof, such that it will not breakreadily from contact with other objects, :or from suddenchanges in temperature, as occurs between sections of vitreous elements, in whichthe change in section between adjoining parts is too-sudden.

' The pocket is additionally shielded, both mechanically and thermally, -.as :by having :theshell extend inwardly of the plug to a position .close to, orlbeyond, itheinnerzend of the cup in prede- 'termined lateral relation thereto, and by this feature, plus a flange at the inner end of the shell extending radially ,OI laterally inwardly over the inner periphery'of the cup and, by thelatter feature, plus the feature of having the ."flange spaced longitudinally-of the cup-or, in any-form, by the {form and;position of the ground-electrode.

Thus they above-mentioned nose-or I tip, ,as provided heretofore, and which is a point of high local heat concentration,is:eliminated, and the proper surface-.creepage distance obtained between the electrodes at the arczone, by means which operates .at considerably reduced temperature,

.By the'propercorrelation of the parts, as herein pointed out, the firing'end of the plug is thus rendered as cool-as-desired, but "still hotenough to prevent the formation of carbon.

mass of porcelain required, and thermally and electrically to control the operating temperature and other characteristics of the insulator.

Referring to- Fig. 1, a plug of the invention comprises, in general, an insulator A, an inner electrode B having an outer terminal C, and a shell D, on which a ground electrode E is supported.

The insulator A comprises a main body portion 5, an outer-end length 6, and an inner-end length I, which, as shown, are all in one homogeneously integral piece of vitreous dielectric material, such as the usual porcelain, although these parts, or portions thereof may be made separately, of the same or different material, and rendered operatively integral in other ways, as by glazing them together.

The shell D, as shown, is like, or similar to, a shell of well-known kind, including a main body portion II), a polygonal, or nut-like, portion I I, an outer-end flange I2, and a tubular inner-end portion I4, of reduced diameter, having exterior screw threads I5, and a radially or laterally inwardly extending inner-end flange I6, between which, and the portion I4, the ground electrode E is supported, as in a usual manner.

The porcelain body portion 5, which is of larger diameter than the diameters of the lengths 6 and I, is of such diameter as to allow for plus or minus tolerance in manufacture, or baking, and still relatively closely fit the shell body I9, with a bottom shoulder I8 over a gasket I9 on a shoulder 20 of the shell D, and a top shoulder 22 under a gasket 23, which is held in place by the flange l2.

As shown, the shoulder I8, the gasket I9 and the shoulder 29, are flat, radially of the plug, but may be of other form, and the flange I2, the gasket 23 and the shoulder 22, slope relative to a radial plane of the plug to, in this instance, facilitate and ensure proper assembly, by pressing the flange to the position shown. The gaskets may be made of copper or other material.

The arrangement of parts issuch that, with all allowances for manufacturing tolerances, the body portion 5 will be tightly held between the flange I2 and the shoulder 20, and effectively sealed by the gaskets 23 and 20, without danger of crushing the inner-end length I against the flange I6. The latter is therefore in freely-spaced relation to the porcelain, longitudinally of the plug. by a distance F, see Fig. 5, which may vary slightly in different plugs.

The inner-end length I which, as shown, has a substantially uniform cylindrical. outer surface laterally spaced from the shell portion M, is provided with an inner-end portion G of inverted substantially cup or pocket-shape, providing a free space H, radially of the longitudinal axis of the plug, for a distance J lengthwise of the plug. This distance is, at least, sufficient to provide proper creepage surface, from a point 25, or adjacent thereto, on the electrode B, along a transverse bottom surface 25 of the cup G, and along an inner longitudinal surface 21 of the cup, to the radially and longitudinally innermost edge 28 of the cup.

Another consideration, determining the length of the surface 21, or the volume of the cup space is, as stated above, the compression ratio of the engine in which the plug is to be employed. If the cup is deeper than this, it will be too cool near its closed end, with the resulting carbon deposits, or fouling, and, if the cup is too shallow, it will not allow the dead air to be displaced far enough from the arc gap to provide for effective firing.

Where it may be desirable to have a conducting part of, or element around, the electrode near the point 25, or at the surface 26, such as a washer-like seal closing the slight space between the electrode B and the insulator A, which is normally filled with cement, the distance J will be sufficient to provide the proper surface creepage distance along the surface 21 or other- Wise. The edge 28 may be rounded, as shown, to increase the creepage path length, and to reduce heating, or the likelihood of chipping.

The distance J, as shown, is also such that the transverse or closed end of the cup, at the surface 26, is disposed a substantial distance K (Fig. 1) from the insulator body portion 5, and also a substantial distance from the shell body portion I 0. and from the mouth end of the cup, thereby avoiding thin section of porcelain over a great length, and facilitating manufacture.

To further assist the latter feature, the surface 21' is also sloping, as shown, or otherwise arranged to increase the thickness of the longitudinal side wall of the cup G from this thickness L, at the mouth end, to the thickness M, at the inner end of the inner side surface of the cup. The distance H, along a radius of the cup, as shown, is greater than the radius of any other inner dimension of the insulator, and greatest near the inner periphery of the inner open end of the cup.

In Figs. 2, 3 and 4, parts corresponding to parts above set forth are designated by corresponding reference characters having the suffixes (a), (b) and respectively.

In Fig. 2, the structure is similar to the structure of the lower portion of Fig.1, except that the pocket Ga is deeper than the pocket G, and

.smaller in diameter at its closed end, and the flange IE0. is thinner, and of larger internal diameter, thus modifying the mass, contour and location of the flange relative to the flange IS. The inner-end insulator length Ia, the tubular shell portion Ida, the threads Ia, and the ground electrode Ea, may be the same as above set forth. In Fig. 3, the cup Gb of the length 1b has an inner surface of different shape, such as curved or parabolical, and the shell portion Mb, having threads I51), is provided without a flange corresponding to the flange IE or H511, and has its inner edge closer to the mouth of the cup.

Also, as'shown in this figure, the ground electrode Eb is made thinner, as by flattening, in its longitudinal length 29, and this length maintained further from the electrode Bb, or equivalently arranged, to reduce the conducting surface adjacent to the mouth end of the cup Gb to accentuate the arcing stress, or localize it, at the intended arcing zone adjacent to the active ends of the electrodes, to reduce the formation of carbon on the insulator or other parts adjacent to the point of juncture of the electrode Eb with the shell, and to resist travel of the are from the arcing zone to the shell.

In Fig. 4, the cup Go of the length 'Ic has an inner surface of further different shape, including a ridge 32 adding further creepage distance, and the shell portion Mc, having threads I 50, is also provided without a flange corresponding to the flange I6 or Ilia, and has its inner edge between the ends of the insulator.

The electrode Ec has a portion 290 joined to the arcing portion proper thereof through a bend or curve 42, which tends to maintain the are at thc'arcing zone, and to resist its travel from this zone through the increased distance on the -electrodeto the shell.

Any of the ;features.shownrin:any of'the figures maybe empioyed-in the place 01" the correspond ing feature in the device of any other figure.

t .e method and structure, illustrated collec tively by Figs. .1, .2, 3, and;e,-provi-de for control ling the operating temperatures and characteristics :of spark plugs, by adjusting the -masses,. contours and locations of the inner-end lengths of the insulators around the inner electrodes to maintain tree spaces longitudinally'oi the plugs ior predetermined. distances, corresponding to the distance ll of Fig. 5, from the inner ends of such lengths, by'the distance H, from said lengths to the innc electrodes, to provide for the com- .pression of substantial volumeof gas in such spaces,,and to avoid excessive differences of temperature between different regions thereof, and adjussing the masses and contours of the metal of, or on, the shells from positions between "the of the inner-end insulator lengths, and of the metal-of, or associated with, the shell is made at -.a location within'the range indicated by Figs. 1, 2, 3 and 4, and as illustrated by a-line N in v5 having its lower inner end opposite'a point corresponding to the inneredge of the flange it offig. l, and its upper outer end corresponding to the bottom of the shell portion Me in Fig. 4; .the congeneric parts of Figs. 2 and 3 being between these limits.

Dotted lines 33, in Fig. -5, indicate the locus of :the outer surface of a solid'of revolution about the longitudinal axis of the electrode B, of the above-mentioned tip or nose, common to standard prior plugs, and "causing. the heating above mentioned. These tips project inwardly, or downwardly, as indicated, various distances and have'shapes other than those shown.

:By a comparison of the lines 33 with the lines :2fi1and 21, the difference is more readily seen between a protrusion or convexity of the porcelain at this point, as in the prior plugs, and a concavity or pocket, as in the invention hereof. This difference, irrespective of the smallness of the parts as actually constructed, removes a substantial proportionor mass of porcelain from a criti cal :zone of heating, and substitutes 'free space in this region. I I'he protrusion or tip, represented by the lines by its tapered or pointed shape, its position on the electrode, and its spacing from the shell,

causes'compression and combustion outside the insulator, whereas, in the plug'of the present invention, this effect is removed from the outside,

andp'laced inside, the insulator cup G.

' Further, in addition to the removal of the above mentioned mass, the substitute mass, represented by the sidesurface of the cup, is placed in a substantially cooler zone protected from heat by the side walls of the bottom inner-end surfaceof the length 'fi substantially conforms to p the electrostatic field.

Dyna-mometer and service tests havedemonstrated that the plugs of my invention produce increased driving torque and horsepower of an engine over a wide range 01 speeds, give an 'automobile smooth pick up in high gear at low speeds, maintain the insulators free from carbon, and the :elctrodesfrom damage, longer than other plugs, and that theyare otherwise a :distinctradvance in theirfield.

The expression oneepiece insulator, as-employed in the specificatio'nland claims, is to be 1 understood as defininga homogeneously integral piece, as set forth, or :an equivalent unit made up'cf a plurality-of identifiable, or originally separate elements,- as distinguished :from ;a plurality of separate insulators which, irrespective of -co- 3 operation thereof with each other, do not make up such unit.

I claim as my invention:

i. In a spark plug, an inner electrode, arr-outer en lengthsprotruding from the shella-nd an inner end cup enclosingua free space around-and extendingradially to, said electrode, the inner :end of the shell enclosing a .ireespace around said cup and havinglits smallest inside diameter no less than the-largest inside. diametei of said cup.-

' metal shell, and -a one-piece insulator surrounding said-electrode in .the shell having an outer end length protruding from theouter endof the shell and an inner end cup protruding-from the inner end of the shell enclosing a free space around, and extending'radially to, said electrode,

the inner endof the shell enclosing a freespace around said cup.

4. In a spark plug,.a shell, a one-piece insulator in the shell, and an inner electrode extending through the insulator, the inner end, of the insulator being of cup-shape adjacent to, and

openv toward, the inner end of the pplug and a length of the insulator constituting a substantial length of the plug protruding from theouterend of the shell having convex exterior surface curvature renderingthesame of gradual taper converging from aposition adjacent to the shell to a position adjacent to the .outerend of the plug.

5. In a spark plug, an inner electrode, an outer metal shell, and insulating meanssurrounding said electrode in the shell having an'outer-end metal shell, and a one-piece insulator surroundelectrode in thelshell having an outer length protruding from the shell, said insulator means extending continuously from said length to aninsulating cup portion thereof at the inner end of the plug,-andthe inner end of .the'shell surrounding said cup in spaced relationthereto andhaving its smallest inside diameter no less than the largest inside diameter of the cup.

6. In a spark plug, an insulator having an inner-end cup portion open toward the inner end of the plug, an outer metal shell including a portion enclosing a free space around said cup portion having a radially-inwardly extending peripheral flange spaced longitudinally inwardly of the plug from the open end edge of the cup and leaving the cup substantially fully open, and an inner electrode extending through the insulator free from lateral protuberances adjacent to said flange.

7. In a spark plug, an insulator having an inner-end cup portion open toward the inner end of the plug, an outer metal shell including a portion enclosing a free space around said cup portion having a radially-inwardly extending substantially fiat-plane peripheral flange spaced longitudinally inwardly of the plug from the open-end edge of the cup and leaving the cup substantiallyfully open, and an inner electrode extending through and beyond the insulator and terminating close to the plane of said flange.

8. In a spark plug, an insulator having an in ner-end cup portion open toward the inner end of the plug, an outer metal shell including a portion enclosing a free space around said cup portion having a radially-inwardly extending longitudinally-inextensive peripheral flange spaced longitudinally inwardly of the plug from the open-end edge of the cup and leaving the cup substantially fully open, and an inner electrode extending through the insulator and through said flange and terminating close to the latter.

9. In a spark plug, an inner electrode, an insulator surrounding said electrode having an innerend cup portion open toward the inner end of the plug, and an outer metal shell including a portion surrounding said cup portion in radiallyspaced relation thereto having a radially-inwardly extending longitudinally inextensive peripheral flange spaced longitudinally inwardly of the plug beyond the open-end edge of the cup, said flange so cooperating with said electrode and having its inner diameter such as to leave the mouth of the cup substantially fully open to the arcing space except for the space occupied in the cup by the electrode.

10. In a spark plug, an inner electrode, an insulator surrounding said electrode having a body and an inner end length of smaller diameter than said body portion including a cup portion freely open to the arcing space and confined entirely within said length having an inner surface of frusto-conical form having its open-end major base at the innerend of the insulator and its minor base only slightly greater in diameter than the diameter of said electrode and spaced a substantial distance from said body, the inner surface of said cup being entirely insulating between said major and minor bases, an outer metal shell surrounding, and spaced from, said cup, and a ground electrode on the shell cooperating wit said inner electrode outside said cup.-

11. In a spark plug, an inner electrode, an outer metal shell, and a one-piece insulator surrounding said electrode in the shell having an outer end length protruding from the shell and an inner end cup entirely local to the inner end of the insulator enclosing a substantial free space volume around and extending radially to said electrode substantially fully open around the electrode directly to the space opposite the inner end of the plug, said shell including a portion enclosing a free space around said cup and having its inner end disposed close to the inner end of the cup.

12. In a spark plug, an inner electrode, an insulator surrounding said electrode having an inner-end cup portion open toward the inner end oi the plug, and an outer metal shell including a portion surrounding said cup portion in radially-spaced relation thereto having ground electrode means and a radially inwardly extending iongitudinally inextensive peripheral flange spaced longitudinally inwardly from the open end edge of the cup, said flange and ground electrode means cooperating with said inner electrode to maintain the interior cup space around the inner electrode substantially fully open directly to the space opposite the inner end of the plug.

13. In a spark plug, inner electrode means, an outer metal shell having ground electrode means, and a one-piece insulator surrounding said inner electrode. means in the shell including an exposed. outer end length protruding from the shell and a short hollow portion local to the inner end of the insulator having substantial inside free space volume, said shell having a length surrounding said hollow portion in laterally spaced relation thereto with the inner end of the shell close to the inner end of said hollow portion and cooperating with said inner and ground electrode means to maintain the inner end of said hollow portion substantially fully open around the inner electrode means directly to the space opposite the inner end of the plug.

14. In a spark plug, inner electrode means, an outer metal shell having ground electrode means, and a one-piece insulator surrounding said inner electrode means in the shell including an exposed outer end length protruding from the shell and a short hollow portion local to the inner end of the insulator closed at its outer end enclosing substantial free space volume about, and extending laterally to, said inner electrode means, an inner end length of the shell enclosing a free space around said hollow portion with its inner end close to the inner end thereof and cooperating with said inner and ground electrode means to maintain said hollow portion substantially fully open around the inner electrode means directly to the space opposite the inner end of the plug.

15. In a spark plug, inner electrode means, an outer metal shell having ground electrode means, and a one-piece insulator surrounding said inner electrode means in the shell having an outer end length protruding from the shell and a short length of substantially cup-shape local to the inner end of the insulator defining free space of substantial volume extending laterally from the cup side walls to said inner electrode means and substantially fully open around said inner electrode means to the area about the inner end of the plug, said inner and ground electrode means cooperating with each other to form a current path through the mouth of the cup.

16. In a spark plug, an outer metal shell having ground electrode means, inner electrode means entirely of conducting material from the outer plug end terminal means to the inner arcing space, and insulator means surrounding said inner electrode means in the shell including a plug closed at its outer end enclosing substantial freesp'ace'volume about, and extending laterally to; said inner electrode means, the openend of said short hollow portion beingclose to the innermost end of the plug andsaid inner and ground electrode means cooperating with each other to form current path means through said openend and to maintainsaid open end substanmany fully open around said inner electrode means directly to the area opposite the inner end or: the plug.

17. Ina sparli'plug; an outer metal shell having "ground electrode means, inner electrode means; and'insulato'r means adapted for only one snore hollow'portion-local to' tlie inner end of the pes iti'on in-the time sur' ounfiin said 'i'nrier lec hollow portiombeing close to-the-innermost end of the plug' and said inner and ground electrode means=cooperating with each other to form-cup rent. path means through said open end and to maintain said open end substantially fully open around saidinner electrode means directly to the area opposite the inner end of the plug.

CARL BERSTLER.

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