US1164113A - Sparking plug. - Google Patents

Description

I. c. ORSWELL. SPARKING PLUG.

APPLICATION FILED APR-26. 1907.

1,1 64,1 13. Patented Dec. 14, 1915.

UNITED STATES PATENT oEEioE.

ISRAEL C. OBSWELL, OF HYDE PARK, MASSACHUSETTS, ASSIGNOR TO ORSWELL IGNI'IER COMPANY,.OF BOSTON, MASSACHUSETTS, A CORPORATION OF MAINE.

' SPABKING PLUG.

Application filed April 26, 1907.

To all whom it may concern:

Be it known that I, ISRAEL C. ORSWELL, a citizen of the United States, residing at Hyde Park, in the county of Norfolk and State of Massachusetts, have invented an Improvement in Sparking Plugs, of which the following description, in connection with the accompanying drawings, is a specification, like letters on the drawings representing like parts.

My invention relates to sparking devices for internal combustion engines, more particularly to the construction of sparking plugs and induction coils therefor.

My invention aims generally to improve devices of this type by providing simple and effective means for increasing the capacity and efficiency of the coil and perfecting the insulation thereof and to that end comprises novel features of construction and arrangement that will be best understood and appre ciated by reference to the following descrip' tion when taken in connection with the accompanying drawings, of a spark plug embodying one form of my invention and selected for purposes of illustration, its scope being more particularly pointed out in the appended claims.

In the drawings; Figure 1, is a vertical and longitudinal section taken through the axis of a spark plug, embodying a preferred form of my invention, selected for illustration herein. Fig. 2, a perspective view illus trating the manner of winding the induction coil. and insulating the secondary terminals thereof; Fig. 3, a similar View of the primary coil to show the manner of carrying in one of the terminals of the secondary and the manner of winding the latter; Fig. 4, a detail illustrating the method of winding and insulating the conducting convolutions of the coils from one another; Fig. 5, a perspective detail of the insulation tabs or strips, to show the method of applying the same to the secondary terminal; and Fig. 6, a perspective detail illustrating the porcelain disk through which the secondary terminals are led to the sparking devices.

Referring to the drawings and to the particular embodiment of my invention selected for illustration therein, I show a sparking plug that is particularly, though not exclusively, adapted for use with internal combnstion engines for automobiles, launches, and the like.

l Specification of Letters Patent.

Patented Dec. 14., 1915.

Serial No. 370,347.

This plug comprises a casing to receive an induction coil and suitable sparking electrodes, uniting in a single and compact structure the essential parts of a sparking device. In the present instance, referring toFig. 1, the induction coil comprises primary and secondary windings efficiently insulated from one another and the metallic conducting portions of the casing. The coil is provided with a core 1, preferably formed of a bundle of soft iron wires, inclosed in a shell or sleeve 2 of suitable insulating material, which, as herein, is preferably somewhat longer than the core, so as to insulate the ends of the latter from the windings of the coil. This core receives the primary winding 3, shown in section in Fig. l, which is suitably wound thereon and comprises, in the present instance, a plurality, herein two, layers of wire having the terminals 4, Fig. 1, led up through the top of a casing 5, with which the spark plug is provided, to suitable binding posts 6 mounted upon its outer end (the top, Fig. 1). Each of the layers of the primary winding and also those of the secondary, presently described, comprise a number of convolutions or strands 7, Figs. 3 and 4 of bare or uninsulated wire and intervening convolutions or strands, 8, of silk or other suitable insulating material, said strands being wound together, side by side around the core or upon an inner layer. By this arrangement the silk strands, which intervene between the adjacent conducting convolutions of bare or naked wire, forfn the only insulating medium between them. The successive layers of the windings of-the coils are'insulated from one another by suitable insulating material, 9, herein preferably sheets of varnished fabric, paper, oil silk, or the like, which are of high insulating properties. Outside of the primary winding, 3, is a layer or shell, 10, of insulating material, upon which the secondary coil is wound, said shell being similar to the sheets 9, described, but preferably thicker effectually to insulate the primary and secondary windings from one another.

The secondary coil or winding, Figs. 1 and 2, comprises a plurality of layers of the relatively fine bare wire, 7, with the intermediate insulating strands 8 and the insulating sheets 9, described. The winding of this coil and the manner of carrying out and insulating its lead wires or terminals ll, 12, is a feature of considerable impor tance. As here shown, suitable tabs or strips 13, 14 of insulating material are laid lengthwise upon said terminals to insulate them from the bare or insulated wires of the sec-- ondary and from one another. While it is a matter of individual preference whether both of these terminals be directly connected to the sparking electrodes or .one of them grounded upon the casing which is in electrical connection with one of the electrodes, l have found the most advantageous results to be secured and provide a more eiiicient strip having a perforation or aperture at its folded end to permit said terminal 11 to be led therethrough to center the same within its insulating envelop.

The terminal, thus insulated, is. laid longitudinally or lengthwise upon the insulating shell of the primary coil, Fig; 3, and the winding is commenced at about one fourth of an inch from the end of the insulation and that end of the coil, the top, Fig. 1, so 7 that the conducting portions of the coil are separated and insulated from this end of the coil. The last turn of this layer and the first'of the next, e'tc., terminate at the same distance from the opposite end of the coil,-

thereby providing. the coil with insulated ends, thus protecting and insulating the bare windings inclosed between the insulating sheets 9. The strands of wire'. and the intervening strands of silk are Wound aroundthe core or shell'until one layer hasbeen provided, when a layer of insulating material,

a such as that described, is wound around it the winding is entirely inclosed or covered by the insulation thus provided. A plural-- with its sides or'endportions extending to the ends of the shell 10.' By this constructlon the conducting portion of this layer of ity of layers are then wound in like manner until the desired number have been provided, each layer being insiflated from those 4 adjacent thereto, and at coil by the sheets 9.

By using uninsulated or hare wire, as dethe ends or the .sci'ihed, the length of the wire employed in tld making a coil of desired size, for-instance that usually provided for spark. plugs, may

he made much greater than the lengthhitherto employed, this being apparent from the tact that the diameter of the hare wire is much less than insulated wire. This controdes. Fig. 2, wherein the last turn of the outer meal in struction therefore permits a greater number of layers of such wire to be used in making a coil of given size or diameter, thereby providing a spark plug coil that, under the usual Working conditions, is of greater capacity or higher potential than those provided with insulated wire.

As hitherto constructed, induction coils that are provided with windings of bare wire have their bare terminals carried outto the opposite ends of the coil and being thus widely separated, no insulation is required. In devices of this type, however, where-it is desirable or necessary'to bring the terminals near together, the necessity for providing eflicient insulation is a matter of considerable importance, more especially where they are carried outto one and the sameend of the coil and also where-the construction of the plug necessitates arranging little space to receive them. The same necessity for providing an eflicient insulation is apparent when the terminals are carried out at opposite ends and one is lead back, either within or withoutthe casing, to connect it to one of the sparking electrodes, which are necessarily in close relation, for without such insulation sparking and short circuit-- ing would take place either between the terr the terminals near together, or PIOVldGS minals, as they are brought near together, or

between the terminal leading from the far' end of the coil and the adjacent portions of the coil, thewcasing, or other parts of the 10o lu I P 1% providing spark plugs or analogous devices with coils having bare windings, therefore, the insulation of the terminals, especially when they are carried out to the same end of the coil should be very eflicient or high to prevent sparking or grounding.

By employing'suitable envelops of insulating material such, for example, as the tabs or strips herein described, for inclosing the exposed ends of the terminals and by also carrying said. e'nvelops'into the body of the coil,'I provide eificient means for efiectually insulating these terminals, so that sparking other than that produced at the sparking electrode-is eliminated.

While, obviously, one of the terminals of the secondary may if'desired be grounded upon the casing of the plug, inthe present instance, Ipreferably carry both terminals ll, 12, Fig; 2, of the secondary out to one and the same end of the coil forconvenience in connecting them to the sparking elec- This arrangement is best shown in secondary winding, shownat. 15 in' the lower left hand corner of said figure, has its terminal carried through an aperture 16 inthe folded end 17 of the insulating strip 14. This strip is also arranged longitudinally upon the coil in a manner similar to that in which the strip 13 is arranged. These folded strips respectively receive the terminals of the secondary, Fig. 2, between their folded portions, said terminals being centrally and longitudinally arranged to extend between the inner surfaces of said portions so that the terminals are completely embedded in insulating material, which insulates them from all conducting portions of the coil or plug. Said strips, 13, 1a, may be made of any suitable insulating material though, in the present instance, I prefer to employ a flexible fabric, such as linen or silk, which is covered with varnish or oil of high insulating properties and which causes the inner faces of the strips to adhere, so that the metal terminals are longitudinally secured in position between the folds of said strips. By this construction, the possibility of sparking between the several strands or layers of either coil and the terminals is prevented, since the latter are completely in- .closed in insulating material. The ends of these strips, shown at the right Fig. 2, and at the bottom of the coil, Fig. 1, are carried out beyond the insulating ends of the coil to insulate the exposed ends of said terminals from all conducting portions at that end of the coil, as will be more fully described. Any suitable means may be employed to secure the inner ends of the insulating strips 13, 14:, in position upon the coil, one method being shown in Fig. 2, wherein the strip 1A is shown as secured to the last layer of the secondary by strips 18 of suitable. material, such as gummed or adhesive paper. The coil next receives a final layer of the insulating material, shown at 19, Fig. 2, preferably composed of the same varnished fabric. Finally, the coil is immersed in a vessel containing an insulating, heat resisting, waterproof varnish or other similar medium. and preferably sterling varnish, which is allowed to soak in until the interstices or spaces between the different convolutions of the windings and the layers of insulating material, and especially between the ends of said insulating lavers at the ends of the coil, have been filled with said varnish or medium. The coil is then taken out and baked or otherwise dried after which this process is repeated one or more times, finally leaving all conducting portions of the coil thoroughly coated and insulated by said medium and the separate parts of the coil pnited into one substantially solid strucure.

As thus prepared, the coil is inserted in a relatively thick removable shell or sleeve 20 .of waterproof, heat resisting, and insulating material, herein mica, which together with said coil is inserted into the tubular metallic casing 5 .of the plug and which is preferably of non-magnetic material.

As here shown, the rear end of this casing 5 is closed by insulating disks or washers 21, 22, and 23, also of mica or like material, which are held in position between the end of the coil and the inturned end, Fig. 1, of the casing. Immediately above this'end of the casing is a block, here shown as a disk 24 of insulating material, for example, mica, which is provided with suitable apertures alined with and to receive the primary terminals 4:. This disk is provided with binding posts, 6, adapted to receive both the primary terminals and the terminals of an electric circuit (not shown) containing a battery, dynamo, or other suitable source of electromotive force and suitable vibration or other interrupting means. These posts and the block of insulating material are held in place upon the head of the casing 5 by any suitable means, here shown as screws 25, the heads, 26, of which are notched to receive said terminals and are retained in the insulating disk 21.

As here shown, Fig. 1, the binding posts are apertured to receive the primary terminals 4, which are maintained in firm conducting contact therewith by means of removable plugs or wedges 4*, which are driven in from the outside and act to close up the apertures and thereby entirely close this end of the plug and prevent the entrance of moisture. At its front end the casing is closed by a cap or head 27, Fig. 1, preferably of metal having a threaded, reduced portion forming a nipple 28, adapted to be screwed into the aperture provided in a wall of the engine cylinder. This casing head rests against an annular mica ring 29, in turn resting against a thick plate 30 of insulating material, herein porcelain, which with said mica constitute a suitable heat resisting medium between the end of the casing and said coil. This plate is provided with a hub like or depending projecting central portion 31, fitting into a corresponding recess 32 in the adjacent face of the head 27. The depending central portion of this head is provided with longitudinally tapered passages to receive tapered hollow shells or conical sleeves 33, of insulating material, preferably of mica which project beyond the threaded end of the nipple 28, and at their inner ends enter suitable recesses 34, centrally located in the depending projecting portion, 31, of said porcelain plate. To hold these sleeves firmly in place within said head, I provide tapered plugs 35, 35, of suitable conducting material, for example, brass and drive them into the open ends of the mica sleeves as shown in Fig. 1. Secured at and within the outer ends of these metallic plugs are the sparking electrodes 36, 37, of suitable conducting material preferably German silver or platinum, the electrodes 36 having a right angular arm 36 and the electrode 3 consisting of a substantially' straight piece of wire. These plugs are driven into said sleeves to such depth that their lower ends, see Fig. l, are above the adjacent ends of the sleeves, the sparking terminals being surrounded by the heat resisting and insulating walls of said sleeves for. substantially their entire length, leaving only their sparking points exposed. By this construction the metallic sparking electrodes are nearly inclosed by a shell of insulating material, all the metal parts of the plug being widely separated therefrom; moreover 'by arranging the sleeves so that their lower ends extend below said metal parts and driving the, conducting plugs in beyond said ends, the possibility of a bridge of carbon deposit being formed between said electrodes or either or both of them or their plugs and the metallic portions of the nipple is eliminated. Moreoverthe oil'that enters or collects in the open ends of the heat resisting mica sleeves is maintained in a liquid state since said sleeves prevent the j conduction of enough heat from the ex- 1 I opening in the mica sleeve 33, to a central longitudinal aperture in the plug 35.where it is secured by means of a taper wedge 88 plosion chamber to, their interior thus .preventing the carbonization of the oil therein.

The porcelain plate, best shown in Fig. 6, is centrally provided with'an aperture in approximate alinement with the central lead wire or secondary terminalll, which is led through said aperture, said recess 34 and the driven in from the outer end of the-plug.

Toprovide for suitably insulating the other secondary terminal 12, the porcelain disk 15 provided witha laterally extending and angular rib 39, Fig. 6, suitably aper-g tured as at to'receive said terminal 12' This aperturefleads inward to the recess 34, which communicates with the opening in l the tapered mica sleeve The secondary terminal 12 is led through this aperture and said'mica sleeve and at its outer end is similarly secured within the'metal plug 35 by a tapered" plug 38*, which maintains .the ter- "minalin electrical. contact with the conducting plug 35 and its. sparking terminal 37.

By this arrangement, the plugs within said mica sleeves effectually seal up all openings and close the plug against the entrance. of

moisture or gases.

An importantfeature of .lates to the thorough and efficient insulation of the secondaryterminals both from the conducting portions of the casing and the adjacent conducting portions of the coils or their core. As here shown, referringto Fig. 2, the tabs or folded strips of insulatin material 13 and. 14, which extend lengthwlse of. and upon the inner and outer surfaces of the secondaries 11, 1.2 are carried out to and extend beyond the lower end of the coil (the right ig. 2) said strips being thick enough my invention reto prevent ruptureby sparking from such adjacent conducting portions of the coil as are of higher or different potential and wide enough to prevent the sparks passing between the secondary engaging faces of the folds of said strips. I

Referring now toFig. 1, the fold 13 of the insulating strip at the inner side of the terminal 18 is folded radially inward across difierent potential and between which a spark might pass, unless properly insulated. As has been stated, the width of the strips is suflicient to prevent sparking laterally or between or across the strips and forms an efficient insulation at the end of the coil. The outer fold 14 of the strip 14 extends downward and is arranged between the circumferential edge of the porcelain plate 30 and the insulating sleeve 20 of the casing thereby increasing the eiiiciency of the insulation atthat point. .Similarly the outer fold 13 of the opposite strip 13 extends out ward radially between the coiled ends of the insulation layer of the secondary and the upper or inner face of the porcelain disk and into substantial contact with the insulating sleeve 20. As here shown, the porcelain plate flattens the ends of the strips out across the adjacent face of the coil, so that the'recess formed between the inner face of the insulating and heat resisting porcelain plate and the adjacent insulatedends of the coil of the secondary is partially filled with a. medium of high insulating properties which also forms a backing to secure the coil in place within thecasing and prevent vibratory movement thereof. If desired, a

suitable waterproof, heat resisting and insulating cement, powder, or other like material, for example, a composition of rotten stone and shellac, .the latter dissolved in alcohol, or varnish and granulated asbestos or mica may also be used to fill orpartially fill this recess and that at the top of the coil, to prevent displacement of the movable parts. This material, represented at' 41, not only perfects the insulation of the coil but also prevents the admission of moisture and the transmission of heat, which'is particularly desirable when the coil is mounted upon parts of relatively high temperature as in the present instance. *l'le the space between the insulated ends of the coil and the porcelain or mica plates may obviously be left vacant, the air therein being a good non-conductor of heat, if a filler is used, it should be composed of heat resisting and non-conducting material. It will be understood by those familiar with the art that spark plugs are subjected to heat of'relatively high temperature and in constructing a coil plug it is exceedingly advantageous to provide it with every possible practical feature that tends to prevent heating it, that does not otherwise impair its efliciency. To this end, the casing, the closures for its ends, the lining shells, the coil, in fact, the entire construction of the plug includes novel features for maintaining the plug at asubstantially uniform temperature,

so that the coil may not be heated and its efiiciency and durability maintained.

The inner face of the rib 39, referred to, extends inwardly at an angle from the center of said plate, as best shown in Fig. 6.

Iii-the positionin which said porcelain plate is secured within the casing, Fig. 1, said rib indents the adjacent end portions 13, 14,

of said strips 13, 14, into the adjacent ends of the insulation layers 9 of the secondary thereby increasing the insulation at that sisting and waterproof, the sparking electrodes being mounted upon the same structure with the secondary coil and directly connected therewith by means of heavily insulated leads, thus avoiding loss by grounding of the secondary or lengthy secondary lead wires. Furthermore, the thick porcelain plate at the lower end of the plug, provides efficient heat resisting means which,

being interposed between the sparking ter minals and the induction coil, prevent injury to the latter by the action of heat.

As will be understood by those skilled in the art, the plug and its contained coil described are adapted to be used with an exteriorly arranged and independent vibrator magnet. The construction'and arrangement of the plug described permits the application of a number of such plugs to the several cylinders of a multiple-cylinder engine while using a single exterior vibrator and vibrator magnet, the primary coils being connected in multiple with eachother and in series with a main circuit containing the vibrator-magnet and source of electrical energy.

This arrangement maintains the induction coils in close proximity to the sparking terminals thereby avoiding the use of exposed secondary terminals or lead wires and securing the practical advantage of a single vibrator for the several coils. The compactness of the plug permits its addition to the engine cylinder, while occupying practically the same space or room as the ordinary spark plug.

So far as I am aware, this is the first instance in the art in which coils composed of windings of bare wire, or coils provide-l with'heavily insulated terminals have been provided for use in spark plugs, thereby eliminating the use of exposed secondary lead wires and auxiliary sparking devices.

One feature of my invention to which especial attention may be directed and which may be embodied in other specific coil con.- structions than that herein disclosed, is the complete insulation which is afforded the secondary lead in passing from the coil to the sparking electrode by means of the continuous overlapping insulating elements which are compactly but efiiciently arranged between the end of the coil and the electrode., 1

While in the embodiment of my invention herein disclosed, the secondary terminals of the spark coil are insulated from one another and the casing and both directly connected to the sparking electrodes, my invention is not limited to such specific arrangement and it is to be understood that I contemplate applying the broad features thereof to spark plugs in which one of the terminals may be indirectly connected to one of the sparking electrodes as by grounding it upon the casing, though I prefer the present construction which is much more efficient.

While in the particular embodiment of my invention herein selected for illustrative purposes only, I have described the same with reference to a spark plug and to a coil having windings of particular type and provided'withinsulating strips of fabric, it is to be understood that my invention is not limited thereto nor to the specific details of construction and arrangement, 1 since the same is capable of modification within wide limits without departing from the spirit and scope of my invention.

1. In a device of the type described, a spark coil having a terminal carried out to extend from one end thereof, means comprising fiat strips ofinsulating material laidlengthwise upon and enveloping said terminal for inclosing and insulating the exposed end thereof from the adjacent conducting portions of said coil, and a pair of sparking electrodes with one of which said terminal is connected.

2. In a device of the type described, a

spark coil having a terminal carried out and extending from one end thereof, flat strips of insulating material laid lengthwise upon and enveloping said terminal and also extending into the coil to cover and insulate said terminal from the adjacent conducting portions of said ,coil, and a pair of sparking electrodes with one of which said termiml is connected.-

In a device of l the type described, a

spark coil having terminals carried out and extending from one'end thereof envelops of insulating material inclosing each of said adapted to-conform to the circumference of the coil without substantially increasing the diameter thereof and longitudinally arranged upon said terminal for covering and insulating it from the conducting portions of said coil, and a pair of sparking electrodes to one of which said terminal is coni nected.

5. A spark plug coil having sparking electrodes, a winding of bare wire, and wire terminals connected to said sparking elee-' trodes, insulating means between adjacent convolutions of said wire, layers of insulating material between adjacent layers of said wire, a layer of. insulating material about the outer layer of said wire, insulating -mean s for protecting said wire terminals,

the last-mentioned insulating means being distinct: from and extending between two adjacent layers of said insulating material, and other cooperating, insulating means leading to the sparking electrodes.

'6. A spark plug comprising a casing, a sparking electrode, an induction coil within sald casing provided with 'a winding of bare wire and a Wire terminal, insulating means for protecting the body of the .coil to insulate the same from the bare windings thereof, and separate and distinct insulating means covering said wire terminal and lead:

ing from. the sparking electrode and terminating at a point within the first-mentioned insulating means;

' '7. In a spark plug the combination of a casing, an induction coil within'sa'id casing provided with a winding of bare wire and a wireterm nal, means for nsulat ng the convolutionsof'sa'id coil from one another, in-

' sulating means for. protecting the otherwise I v i eais bare and exposed end of said terminal and also extending into the body of the coil and terminating within the insulation of the bodyv of the coil to insulate the wire terminal from the bared metallic windings of the coil, a filler of insulating material for sealing the end of said casing adjacent said terminal, and a pair of sparking electrodes with one of which said terminal is connected.

8. A spark plug having a casing, a coil within said casing having primary and secondary windings, the latter being wound with bare wire, means for insulating the convolutions of said wire from one another, means whereby the casing may be attached to an engine cylinder, a-sparking electrode, a

bare wire secondary terminal leading from the I attaching'end of the casing and connected 'with said electrode, and continuously arranged but individually distinct insulating elements extending from said electrode to and terminating within and-"overfllaidby the insulation of thebody of thefcdil for insulating said otherwise bare t fmil lal.

9. A spark plug having a casing, a coil to provide a continuous insulation for the a I terminals.

ing a head adapted to be secured to an engine cylinder, sparking electrodes carried by said head, van induction coil within said 10. A spark plug comprising a casing havcasing having windings of bare wire with means for insulating the adjacent convolutions from one another, a wire terminal carried out'to the end of the coil adjacent said head -and connected to one of said electrodes,

and an envelop of insulating material dis v tinct from said convolutions insulating means for inclosingand insulating the portion ofthe otherwlse bareiwire terminal int-rmediate said coil and said head, said envelop extending within and being inclosed and overlaid by the insulating means of the body of the coils 11. A spark plug comprising a casing having a head adapted to besecured to an engine cylinder,"sparking electrodes carried by said head, an induction coil wi thin said casing having windings of bare wire with means for in'sulatin the adjacent convolutions from one anot er and a wire terminal carried out to the end of the coil adjacent said head and connected to one of said electrodes, an envelop of insulating material distinct from said convolutions insulating means, and inclosing and insulating the portion of the otherwise bare wire terminal intermediate said coil and said head, said envelop extending within and being inclosed and overlaid by the insulating means of the body of the coil and a filler of insulating material for insulating the end of the coil adjacent said head.

12. A sparking plug provided with a casing having a head provided with means for attaching it to an engine cylinder, an induction coil wound with bare wire within said casing having one of its bare wire terminals carried out to the end of said casing adjacent said head, means for insulating the convolutions of said wire from one another, a plate or disk of insulating material between said head and the adjacent end of the coil, and provided with means to receive said terminal, and an envelop of insulating material distinct from said convolutions insulating means for inclosing and insulating the portion of said terminal between said plate and the adjacent end ofthe coil, said envelop extending within and being inclosed and overlaid by the. insulating means of the body of the coil.

13. A sparking plug provided with a casing having a head provided with means for attaching it to an engine cylinder, an induction coil within said casing having one of its terminals carried out to the end of said casing adjacent said head, a plate or disk of insulating material between said head and the adjacent end of the coil, and provided with means to receive said terminal, an envelop of insulating material for inclosing and insulating a portion of said terminal between said plate and the adjacent end of the coil and a heat resisting filler for filling the space between said plate and said coil and enveloping said terminal.

, 14. A spark plug having a casing, an induction coil within said casing having its terminals carried out to one end of the coil, an insulating plate at the terminal end of said coil and provide with recesses, shells of insulating material arranged in said recesses to receive said terminals, and envelops of insulating material for insulating the exposed portion thereof and the adjacent conducting portions of said coil, each of the envelops having end portions extending laterally between the end of said coil and the adjacent face of said plate.

15. In a device of the type described, an induction coil having terminals carried out and extending from one end thereof and envelops of insulating material for each of said terminals for insulating the exposed ends thereof, an inner portion of each of said envelops extending across. the end of the coil and providing a double layer of insulating material between vsaid terminals and the conducting portions of said coil, a casing in which said coil is mounted, a plate of insulating material for closing said casing at the terminal end of said coil and provided with means to receive said terminals, said plate being arranged to press the ends of said envelops against the adjacent end of the coil and supporting the latter within said casing, and sparking electrodes with which said terminals are connected.

16. A sparking plug for internal combustion engines comprising a casing, an induction coil arranged therein having primary and secondary windings and a secondary terminal carried out to one end of said casing, a plate for closing the end of the casing adjacent said terminal and provided with means to receive said terminal, a head exterior to said plate and secured to said casing and provided With means to adapt the same to be attached to an explosion engine, an envelop of insulating material for said terminal, means for insulating the exposed portion of said terminal between the end of the coil and the inner face of said plate and to prevent sparking between said terminal and the adjacent conducting elements of said coil or said plug, an insulating shell carried by said head, a metallic conducting plug carried thereby, means for securing said terminal thereto, and a sparking electrode carried by said conducting plug.

17. A spark plug comprising a casing, a coil therein provided with a plurality of convolutions of bare wire, intervening convolutions of insulating material and an outer layer of insulating material, and a terminal also of wire provided with an insulating envelop distinct from said material to prevent sparking between said terminal and the adjacent wire conducting portions of said coil or said casing, said envelop commencing within the body of the coil intermediate said outer layer and the adjacent layer of the wire and extending beyond the end of the coil to insulate said terminal from the adjacent conducting portions at the end of said coil, and sparking electrodes to one of which said terminal is connected.

18. A spark plug provided with a casing, ahead therefor, a coil within said casing, an

insulating shell mounted on and projecting outwardly beyond said head, and a sparking electrode having its inner end secured at a point within and inwardly beyond the outer end of said shell, the latter projecting-from said head and enveloping said electrode beyond the point where it is secured to a point adjacent the sparking terminal thereof.

19. A spark plug having a casing, an induction coil therein, the latter provided with a secondary wound with bare wire, and wire terminals, a sparking electrode to which one of said terminal electrodes is connected, an insulating body at the terminal end of said secondary winding, through which-insulating body the said secondary terminal. passes, and an insulating envelop inclosing an otherwise bare wire terminal and extending into and terminating Within the body of the coil and filling a portion of the'space between the said body and the coil. h

, 20. A spark plug having an induction I coi1,-an insulating plate at one end thereof, insulating material between said plate and said coil, a terminal passing from said coil two subscribing Witnesses.

ISRAEL 0. oRsWELL Witnesses:

ROBERT H. KAMMLER, SIDNEY F. SMITH.

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