US2571769A - Ignition device - Google Patents

Description

Oct. 16, 1951 1 H. SEGALL IGNITION DEVICE Filed Sept, 27, 1947 IN V EN TOR.

AT TOR NEN Patented Oct. 16, 1951 IGNITION DEVICE Louis H. Segall, Sidney, N. Y., assignor to Bendix Aviation Corporation, New York, N. Y., a corporation of Delaware Application September 27, 1947, Serial No. 776,600

8 Claims. 1

`This invention relates to ignition apparatus and more particularly to a combined spark plug and transformer coil unit adapted for use in the ignition system of an internal combustion engine.

One of the objects of the present invention is to provide a novel radio shielded spark plug and transformer coil unit which is simple in construction, durable, and reliable in operation.

Another object is to provide a unit of the above character having a relatively small number of parts.V

Another object is to provide novel simplified means for mounting a transformer coil in a shielded spark plug.

Still another object is to provide a shielded spark plug having a transformer coil which, through the provision of novel mounting means therefor, is held in its proper position by friction, thus materially simplifying l construction and assembling of the various parts of the spark plug and decreasing manufacturing cost thereof.

A' further object is to provide a shielded spark plug and transformer coil unit having an expansible conducting element which operates to hold the coil in proper position in the spark plug and to connect the high voltage or secondary winding of said coil with the center electrode of said spark plug.

A still further object is to incorporate a transformer coil in a shielded spark plug in a novel manner whereby said coil is supported by the center electrode assembly and is completely enclosed in an insulating compound so as to seal the same against moisture and to substantially eliminate or minimize danger of flashovers.

- These and other objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for the purpose of illustration onlyv and is not intended to define the limits of the invention, reference for this latter purpose being had primarily to the appended claims.

' In the drawing, the single iigure is a longitudinal sectional view of one form of spark plug embodying the present invention.

The single embodiment of the invention illustrated in the drawing, by way of example, includes a radio shielded spark plug of the type now in common use on aircraft and similar engines. In the form shown, the spark plug comprises a tubular metallic shell III which is externally threaded at II for cooperation with a threaded opening in an engine cylinder (not shown), and is provided with an upwardly extending metallic shielding barrel I2 which may be integral with or otherwise suitably secured to said shell. For purposes to hereinafter appear, the inner diameter of barrel I2 is larger than the inner diameter of shell I0, and the bore I3 extending through said shell is provided with a tapered wall portion I4.

Secured to the lower end of shell I0, as by silver solder or any other suitable means, is a ground electrode I5 which may be of any suitable known construction and cooperates in spark gap relation with the exposed lower end of a center electrode I6 that is mounted in the bore of a ceramic or the like insulator II for conducting high tension electrical current therethrough. Center electrode I6 is electrically connected to a terminal plug I8 which is disposed at the upper end of insulator II and extends into the bore of said insulator.

The center electrode assembly comprising electrode I6, insulator II, and plug I8 is preferably mounted in shell I0 in such a manner as to pre- Vent any gas leakage between said insulator and said shell. This mounting is effected by wedging a sleeve I9 of relatively soft metal, such as copper, between a surface of insulator I'I and the tapered Wall I4 in shell I0. The sleeve engaging surface of insulator I'I may be coated with a thin layer of powdered graphite, a soldering flux or the like, and may also be provided with a slight taper.

A transformer coil is slidably mounted in barrel I2 in a novel manner whereby the mounting of said coil in said barrel and the electrical connections therefor with a supply lead and with the center electrode I6, I8 are materially simplified without affecting the eiciency of the spark plug. In the form shown, the transformer coil comprises a tubular core 20 of magnetic metal. This core preferably consists of a few turns or layers of sheet metal, such as silicon iron, forming a laminated tube which surrounds and extends above the upper end of insulator Il in the annular space between the latter and barrel I2. In order to guard against flashovers of high tension current, the upper and lower ends of core 20 are spaced a safe distance from grounded parts of the spark plug. The outer surface of the metal of said core is coated with a thin lm of suitable electrical insulation, such as enamel, to reduce eddy current losses to a minimum.

One or more layers 2| of insulating material are wound around core 20 and a secondary coil 3 winding 22 is then applied thereto, the several layers of said coil winding being separated in a well-known manner by layers of insulating sheet material 23. A primary winding 24, which may consist of a single layer, is wound around the last insulated layer of the secondary winding 22 and is, in turn, surrounded by a two-ply insulating layer 25. l,Surrounding insulating layer 25 is a split sleeve 2S Vof magnetic metal, such as silicon iron, which acts as a path for magnetic ux in conjunction with core 20.

It is to be noted that the several layers of primary and secondary coil windings 24, 22 do not extend longitudinally beyond .the length of .core 2il, and that the initial or first layer of the secondary winding is space wound to accommodate the high frequency potential `and to prevent ilashovers between the turns thereof. Additionally, the insulating layers 2|, 23, 25 extend an appreciable distance beyond the opposite ends of primary and secondary windings 2.4, 22 and are ,spaced inwardly from the opposite ends of barrel I2 to` further shield said windings from groundedpartsnf the spark plug. In a commercial embodiment, the primary and secondary coil windings 2.4, 22 consist of 25 turns and2000 turns, respectively, of Formvar.No. 25 .and No. 42, respectively, *heat resisting enamel covered copper wire, and the insulating layers 2|, 23 and 25 are made of a -polytetrailuoro-ethylene material known as Teflon which is a plastic nlm having good heat .resistance and dielectric properties. In the interest of clarity, all of .the insulating layers are shown as single lines in `the drawing.

The high potential end of secondary winding 2 2 is connected, such asby a thin strip conductor 243, -to thecore 26 which, in turn, Ais connected to theV terminal :plug I8 of the center electrode assembly lby means of an `expansible conductor element Yin the form vof an `open wound tension coil spring 28 made Iof a suitable electrically con.- ductivezmaterial, such asstainless steel. Normally, ,the outside ,diameter vof conductor spring 28 is slightlylarger than-the insideadiameter of core sothatwhen saidspring is placed within said core it will-.byits expandingaction in a radial direction engage the uncoated inner surface of the core .with Vsuflicient pressure .to not only make good electrical-contact therew-ith but to hold the coil 4assembly .tightly and support the same on the center electrode yassembly in pro-per position lengthwise-of barrel I2. 'Conductor strip V2'I is disposed between the insulating layers 2-I, -23 and extends through the layer 2| and is thus Vkept clear of the grounded parts of the spark plug.

Projecting into the yupper endof coil unit 22, 2 andtting tightly in the bore formed by the inner Yinsulating layer 2| is atapered plug 2-9of ceramic-or other insulating material. This latter plug Vis provided-with a straight lower portion 30 of reduced diameterwhich extends loosely into the bore ofcore 23 and'forms an external annular shoulder 3l whichengages the upper end of said core. The lengthof plug 25| is so chosen that when the shoulder '3| thereof vis engaged with core 29 as above described, the conductor spring 28 will be properly positioned thereby -between the ends of said-core, whereupon the coil unit 22, 24,

.through engagement of said spring with the terminal Aplug I8 of the center electrode assembly. will be supported by-said assembly in proper positionlengthwise of-'barrel VI2 and provide a space above and belowthe same as indicated at S, S, for receiving a vfilling compound, as hereinafter de- `.opposite end of which vis `connected, as by means ,of silver solder, to an .input terminal 34.

The connection 32 is made between the plies of the 4AOuter insulating layer 25, and the conducting strip 33 extends upwardly therefrom between said plies into the upper space S in barrel I2 and across the upper end'of plug 29. Conducting strip 33 is made of good electrically conducting material, such as pure nickel. The opposite or other end ofprirnary winding 2.4 is connected to ground by 'connecting it to the barrel I2 as at 35 through a thinconducting strip 36 which is similar to the conducting strip 33 and extends upwardly between the plies of the outer insulating layer.25.

The input terminal .3d is in theform of a pin made of high grade steel and is xed in .a glass seal 31 -which is molded orcemented in a flanged tubular member 38 which extends into the upper vend of barrel I2 and servesto hold the coil assembly in place in said barrel. Input terminal 34 projects beyond the -lower surface of Ymember ,3,8 to have the conducting strip .33 connected thereto, and when said member is `inserted in barrel I2 the end of .said stripis pushed into a'cavity 39 formed in plug 29 to take up the slack. One or more thin washers .lill of insulating material are engaged 4over the .lowerend of terminal `34 before conducting strip 33 is connectedthereto in order to insulate said stripirom the lgrounded member. .In the final assembly, :theangeof member 13S is engaged with the upper end vtof barrel I2 `and-said member is secured to saidbarrel by a series of overlappingspot welds which provide a press fit and insure a moisture tight seal. Theouter end .fof member 38.is 'externally threadedzfor receiving Ya shielding conduit for :an incoming supply lead (not shown) which maybe ofstandard size and known construction.

After member 38 is secured in place, thespaces` S,.,S .within barrel `I 2,-the cavity 39,' and thespaces around and inside the .coil unit-are lled vwith a suitable insulating compound 4|, such as forexample, ,a compound' commercially known ,as lfStyrene .base Q 447, manufactured by .Dow Chemical Company. For this purpose, theshell IU vis Vprovided with a port 13,2 which lopens 'outwardly through the side of said shell and `communicateswith the lower space S in barrel I2.

' Before lling the spark plug with .the-insulating compound Vil the entire vassembly is placed in `an ovenfor approximately to 8 hours at about 150 Fahrenheit for precautionary drying out ofthe same. The spark plug is then placed in atank and evacuated at 25 to` 28 inches vacuum afterV which the insulating compoundlll `is forced into the spark plug 'through the `port 42under at.- mQSpheric vpressure .iorapproximately ve min-,- utes to insure nlling ofthe spaces S, S, thecavity 39, and all the void spaces around ,and inside ,the

coil assembly. If desired, pressure above atmospheric pressure may be employed for introducing the lling compound into .barrel l2. The

n port 152 is then -closed by a taper .pin .plug 43 to; retain the liquid compound in the barrel .|2,

said plug being Ydriven into said port and thereby'. exerting additional pressure on the fillingV com? pound. The filled spark .plug is then allowed Ito' stand for a time interval to permit setting of the llling compound to a solid mass of a resilient non-moldably material, but this setting may be accelerated by baking said plug for approximately fifteen hour at 140 Fahrenheit or four hours at 200 Fahrenheit. The compound 4| contracts about ten percent in setting and provides a good seal around the inner circumference of the spark plug to guard against flashovers from the high tension windings, and because of the hermetic sealing of barrel I2, said compound will withstand the high temperatures with which the spark plug is subjected under, operating conditions. For the sake of clarity, the filling compound 4l is not shown in the spaces around the coil assembly.

There is thus provided a novel combined radio shielded spark plug and transformer coil unit which is simple in construction, has relatively few parts, and wherein the mounting of the transformer coil and the electrical connections therefor with a supply lead and with a center electrode is materially simplied through the provision of novel mounting means. Additionally, the novel construction and arrangement of the transformer coil and mounting means therefor substantially eliminates or reduces to a minimum the danger of flashovers within such a unit.

Although only a single embodiment of the invention is illustrated and described, it is to be expressly understood that the same is not limited thereto. The transformer coil and mounting means therefor may be embodied in spark plugs of other constructions, such as those having mica insulation instead of ceramic. Various Vother changes may also be made, particularly in the design and arrangement of parts illustrated and in the materials mentioned without departing from the spirit and scope of the invention as will now be clear to those skilled in the art. For a definition of the limits of the invention, reference is had primarily to the appended claims.

What is claimed is:

1` In apparatus of the class described, a tubular metallic shell, an insulated center electrode assembly mounted in said shell and projecting therefrom, a metallic shielding barrel extending from said shell around and beyond the projecting end of said assembly, an ignition coil slidably mounted in said barrel and comprising primary and secondary windings, a tubular metallic core for said coil surrounding the outer end of said assembly, means for connecting the high potential end of said secondary winding to said core, and means disposed within said core for mechanically supporting said coil on the outer end of said assembly and for electrically connecting said core with the electrode of said assembly, said last-named means comprising a radially-expansible open-wound coil spring arranged with its axis parallel with the axis of said core and engaging the electrode of said assembly and the inner surface of said core under radial tension.

2. In apparatus of the class described, a tubular metallic shell, an insulated .center electrode assembly mounted in said shell and projecting therefrom, a metallic shielding barrel extending from said shell around and beyond the projecting end of said assembly, an ignition coil slidably mounted in said barrel and comprising a tubular metallic core surrounding the outer end of said assembly, an open wound coil spring disposed within said core and engaged with the latter under radial tension and with the outer end of said assembly for supporting said coil on said assembly in pre-determined position with respect to the llongitudinal axis of said barrel, and a ta- 6 pered plug of insulating material tightly fitted in and carried by said coil for properly positioning said spring axially with respect to said core.

3. A combined spark plug and coil unit comprising a tubular body member, an insulated electrode assembly mounted in said member and projecting upwardly therefrom, a shielding tube extending from said member around and beyond the outer end of said assembly, an ignition coil slidably mounted in said tube and surrounding the outer end of said assembly, said coil comprising a tubular metallic core and primary and secondary windings thereon, means for electrically connecting said secondary winding with said core,a radially-expansible open-wound coil spring disposed within said core and having portions thereof engaged with said core and with said assembly, said spring operating to electrically connect said core to the electrode of said assembly and exerting radial pressure against the inner wall of said core to mechanically support said coil on said assembly so that the opposite ends of the coil are spaced inwardly from opposite ends of said tube, a plug of insulating material tightly fitted in said coil for positioning said spring axially with respect to said core, a metallic closure member for closing the open end of said tube and spaced from said coil, an elongated terminal in said closure member and insulated therefrom, said terminal projecting into the space in said tube above said coil, means for electrically connecting said primary winding to said terminal, and insulating means filling the spaces in said tube above and below said coil.

4. An ignition unit comprising a tubular core of magnetic metal, primary and secondary windings on said core, said secondary Winding and core being electrically connected, and a radiallyexpansible open-wound coil spring of electrically conductive material disposed within said core'and engaging the inner surface thereof under radial tension.

5. An ignition unit comprising a tubular core of magnetic metal, primary and secondary Windings on said core, said secondary winding and core being electrically connected, a radiallyexpansible open-wound coil spring of electrically conductive material disposed within said core and engaging the inner surface thereof under radial tension, and an insulating plug extending into and engaging the end of said core and positioning said spring axially with respect thereto.

6. An ignition unit comprising a tubular core of magnetic metal, a secondary winding on said core, a primary winding on said secondary winding, insulating sheets between adjacent layers of said windings and between the inner layer of said secondary winding and said core, said insulating sheets extending beyond said layers and said core and said secondary winding being electrically connected to said core, a radially-expansible openwound coil spring disposed Within said core with its axis parallel with the axis of said core and engaging the inner surface thereof under radial tension, and an insulating plug in one end of said insulating sheets and projecting into and engagmg the end of said core for positioning said spring axially with respect to Said core.

'7. In apparatus of the class described, a coil comprising a tubular metallic core and a plural layer winding thereon having sheet insulating material between and extending axially beyond the layers thereof, and an insulating plug having a tight fit in said projecting insulating material,

il .said plug having .an :annular :shoulder :engaging .the endlof saidicore. y 8. VInapparatus -fof `the class described, la metal- .lie-bamtel, an insulated electrode :projecting into said lharrel, .a Vcoil having sheet insulation .between and :extending axially beyond the vlayers fof the .coil winding, and :means .for positioning fsaid coil around one ,end `oi .said insulated electrode intermediate the ends of said Vbarrel comprising an insulating block havinga vtight tin said projecting sheet-,insulation and a-radially expandable .conductor Iengaging Athe yinternal -Wa'll gof :sadcoil `under 'tension :and interposed between `said 4electrode and said block. LOUIS -SEGALL REFERENCES CITED .The following references are of vrecord iin the le 'of this patent:

UNITED STATES PATENTS Number Name Date '2,`266;614 Robinson Deeil, L19411 12,327 ,1784 Hartzell Aug. "24, .1943 254003564 Mittermaier May 41451946 1214145692 Harkness Jan. 2l, 1947 22,461,098 Weatherly Feb. 18, 1949 :21,482,884 Tognola etal. .Sep.t.i27, S1949

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