US2632132A - Spark plug - Google Patents

Description

March 17, 1953 v DELANQ 2,632,132

SPARK PLUG Filed June 15, 1951 INVENTOR. JAMES 1K DEL/1N0 Patented Mar. 17, 1953 UNITED STATES PATENT ()FFICE SPARK PLUG James Kendall Delano, Rye, N. Y. Application June 15, 1951, Serial No. 231,769

'7 Claims.

This invention relates to spark plugs, and particularly to a spark plug construction suitable for use in aircraft, engines at high altitudes.

In the type of service when planes frequently climb and fly at high altitudes, the ignition system of the engine is affected, ,due to the rarefication of the air. As the air pressure drops, the electrical leakage losses increase, and more voltage is required to provide adequate voltage at the spark plugs for the ignition. Unless this loss is prevented, the height to which a plane can climb becomes limited.

Various means have been employed to overcome this trouble. The principal remedies used today are the pressurized system where all the ignition equipment including the magneto, the wires, etc. are kept under pressure and all high tension leads are placed in tubing and an air pump driven from the engine keeps the pressure in the tubes at around ground air'press'ure.

Another system uses a low voltage magneto and supplies transformers to step up the voltage to the plugs. The transformers are located very close to the engine plug so only a short wire is required to supply each plug. This cuts down the losses that would result from long high voltage leads, but does not eliminate all the loss.

Another type of ignition employs a medium voltage magneto and encloses its high voltage transformer in the body of the spark plug, but in turn the terminals and parts permit air leakage due to contraction and expansion and, where the pressure decreases during a flight, the reduced pressure allows the high voltage to flashover inside the plug.' This fiashover carbonizes the insulation and the plug ceases to function.

The transformer being very small so that it may be incorporated in a plug of this type is very limited in insulation on account of the small winding space, and it takes very little loss of ground air pressure to cause a breakdown. Great diificulties are met in trying to keep the wire terminals tight. In a plane flying from tropic to frigid temperatures or from ground to mountain heights, the expansion and contraction soon produce leaks that allow the pressure to escape during flights at high elevation.

To overcome the foregoing difficulties, the present plug is provided, as disclosed herein, that keeps its high voltage parts under high pressure at all times while the engine is operating.

One object of the invention is to provide an integrated spark plug, to which only. low voltage energy need be, supplied, from asuitable low voltage s e and in wh h the hi h voltage 2 required for the operation or breakdown of a spark gap will be generated by a suitable transformer in the plug itself.

Another object of the invention is to provide a spark plug in which a high-pressure atmosphere is maintained during operation of the engine in which the spark plug is inserted.

Another object of the invention, bearing upon the functional and structural features of the spark plug of this invention, will be more readily appreciated on reference to the accompanying specification and description of the drawings in which:

Fig. 1 is a vertical elevational view of an assembled spark plug with a portion broken away to show the manner of connection of an external distributor lead to the input terminal thereof;

Fig. 2 is a vertical sectional view taken of the plug itself, taken along the line 22 of the plug shown in Fig. 1;

Fig. 3 is a bottom end view of the plug of Fig. 1, showing the disposition and construction of the spark ap electrodes;

Fig. 4 is a horizontal sectional view taken downward at a plane along the line 4-4 through the body of the plug, as, shown in Fig. 2.

As shown in the drawings, a spark plug it embodying the principles .of this invention comprises an input terminal -I I, a voltage transformer I? for stepping up a low input voltage to a high output voltage, and a spark gap l3 at the bottom end of the plug to be energized by such high volt age. The foregoing elements are supported on the structure of the plug, which includes a base I 4 which serves as the foundation support for the entire plug. An enclosing shell 15 threads onto the base l4, against a pressure-sealing gasket l6, and serves to support the transformer 52.

The base member I4 is shaped to include an externally threaded tubular section I"! depending from a flanged main body portion 18 and having a short co-axial tubular section is extending about the flanged body portion [8. The threaded tubular portion i-l serves as an insertion plug for insertion in a correspondingly threaded hole in the wall of acylinder head of an engine on which the spark plug is to be used. The insertion plug H has an inner cylindrical bore 2!, and at its lower end supports'two electrodes 23 and 22 that constitute the cooperating electrodes of the spark gap or space between the two electrodes. The electrode 23 is supported directly at the lower end of the threaded tubular section ll, and consists of a disk-shaped element having an annular rim :4 nq a plurality .Of symmemtauy .dis-

posed polar portions 25 extending radially inward from the rim 24 to a distance closely spaced from the peripheral surface of the axial electrode 22. The flanged main body portion E8 of the base member M is formed, as shown in Fig. 1, to constitute a hexagonal nut, to enable the spark plug to be manipulated by a wrench for tight insertion into a cylinder head or for removal therefrom.

The plug base supporting member M is provided with a spherical seat 2? on its inner surface to receive a correspondingly spherically shaped boss 23 on an insulator 29 which serves as a partial support for the center or axial electrode 22 at the spark gap.

The upwardly extending threaded portion IQ of the base support i l is provided with internal threads 3i and external threads 32. The internally threaded section accommodates and receives a lock nut 33 which serves to clamp the insulator support 291 in fixed position upon the base supporting member it, through the medium of two annular gaskets 3d and 35 respectively disposed between the spherically-shaped insulator boss 28 of the insulator body 28 and the seat 21, and between the insulator body 23 and the lock nut 33.

The external threaded section 32 of the plug supporting member i l accommodates and receives the enclosing shell l5, which is shown internally threaded along the lower portion of The transformer l2 comprises a spool lli of insulating material of ceramic or other suitable material having a hollow tubular body M and two end flanges :32 and d3 with a short co-axial tubular extension or apron id extending coaxially from the end flange 33. The upper spool flange E2 is provided with a small hole 52-11 therethrough to accommodate a wire conductor 65 then from the primary winding of the transformer to a terminal anchor screw M5 which serves also to anchor a terminal spring 4.! in position at the top of the spool to engage the undersurface of the input terminal ll. v

The lower spool flange 13 is similarly provided with a hole at therethrough to accommodate a conductor 43 leading from a primary terminal of the transformer winding to a grounding copper washer 5i) resting on a threaded lock nut 5|. The lock nut 51 is shown provided with openings 53 to receive a spanner wrench by means of which the lock nut 55 may be tightened or loosened, upon insertion in or removal from the enclosing shell it.

By means of the lock nut 5i the transformer spool assembly may be pressed home tightl with the contact spring ll pressing against the under surface of the input terminal i l, thereby to clamp the transformer tightly in flxed position.

The transformer i2 is provided with a primary winding 55 and a secondary winding 56. The primary winding is of a relatively small number of turns, and the secondary winding 55 has a relatively large number of turns, as is well understood in the art, in order to provide a stepup transforming action whereby a current of low voltage supplied to the primary winding will induce a high voltage in the secondary winding 56, in accordance with the ratio of the number of turns. The windings 55 and 56 are separated by an insulating sleeve 51.

The circuit of the primary winding 55 proceeds from the input terminal H through the contact spring ll and thence through the winding 55 itself to the other terminal 4 of that winding, which is then grounded on the copper washer 5d, which is in direct metallic contact and therefore electrical contact with the lock nut 58, and thence through the shell 15 down to the body of the plug supporting member M, which will be grounded on the engine block in which it will be inserted for operation. The secondary winding 56 has one terminal also connected to the grounding lead is in order to be grounded on the metallic structure of the plug. The other terminal of the secondary winding, which is the hot terminal, is connected to the magnetic iron core 58 of the transformer to provide a terminal to which electrical and mechanical contact may be readily and easily made during assembly in order to provide an electrical connection from the hot terminal of the secondary winding to the axial electrode 22 at the spark gap.

The electrical connection from the core of the transformer is made to the axial electrode 22 of the spark gap by means of a simple assembly consisting of a cylindrical rod cc axially recessed at its upper end to accommodate a metallic conducting spring Si disposed to seat between the lower end of the core 53 of the transformer and a floating contact and valve 52 seated in the bottom of the recess in the upper end of the rod fit, in order to establish an electrical contact between the core 58, as one electrode terminal of the secondary winding, the rod to which is electrically connected at its lower end to the axial spark gap electrode 22, thereby providing an electrical connection from the high voltage terminal of the secondary winding to the spark gap electrode 22. The rod Ed has a central axial narrow passage (53 throughout its length that is normally closed by the contact valve 62 by pressure of the spring El for a purpose to be eX-i plained below.

Since the rod es must carry the high voltage from the secondary winding of the transformer to the axial electrode 22 of the spark gap, the rod 60 constitutes a high voltage conductor and is supported in the insulator 29, to insulate that high, voltage connection from the common grounded metallic structure of the plug. The upper end of the insulator 29 is confined within the depending tubular extension or apron 4 3 which serves to insulate that conductor further from the lock nut 5i.

By means of the construction that is shown, the input terminal H and the transformer unit I2, together with the copper washer 59, are tightly assembled as one unit in the upper part of the shell 15 by means of the tightened lock nut 5i. The insulator 29 is assembled on the plug supporting member M by the threaded lock nut 33 together with the two sealing gaskets 34 and 35, to position the two electrodes 22 and 2-3 of the spark gap in suitable symmetrical relationship. The upper and the lower parts of the plug may then be easily and readily assembled by threading the enclosing shell it) onto the outer threaded portion 32 of the upwardly extending tubular portion it of the base plug i4, since the electrical connection will be established and maintained by the conducting compression spring 6!, between the core as a terminal of the secondary winding and the rod 613 as a terminal for the connection to the spark gap terminal 22.

The input terminal H is suitably tightly locked in position on a reduced head portion 64 of the shell I5, being suitably insulated by insulating tubes 65 and 66 and the annular seating washer 6'1.

When an energy pulse is fed from the external ignition control system to the input terminal l! of the plug, that pulse will generate a correspondingly high voltage pulse in the secondary Winding of the transformer, and that high voltage pulse will be transmitted to the axial electrode 22 at the spark gap. The high voltage between the two terminals at the spark gap will cause an arc to be made across the small gap, which will ignite the explosive mixtur compressed in the cylinder and existing between the electrodes of the spark gap. The heat from that ignition will be imparted to the small volume of explosive mixture in chamber 2 l, with consequent expansion of the quantity of that mixture in the chamber 2!. The quantity of the mixture in chamber 2! will thus be heated before the surrounding mixture in the cylinder, with consequent expulsion movement of some of the explosive mixture in the chamber 2!. Th expulsion movement moves the spark slightly for ward and outward into the compressed mixture in the cylinder and thereby assures increased heat exchange between the arc and the compressed mixture in the cylinder.

At high altitudes the low pressure rarefied atmcsphere has less insulating value than norma pressure atmosphere at sea level.

In order that the transformer will not break down in the high altitudes and cause an elec tric leakage to be effected between turns of the transformer windings and the enclosed shell, gas pressure is supplied into the enclosing shell i5, from the engine cylinder in which the spark plug is inserted. Such gas pressure enters the enclosing shell through a small hole 58 in the spark gap electrode 22 that communicates with the small hole 63 in the rod 60. The hole 53 in the rod is normally closed by contact 62 which serves as a valve element under the biasing force of spring 5!. The valve seals off any pressure that may have passed the valve and entered the shell IE to immerse transformer Ml. Whenever any pressure within this space is lost, it will be replenished by further movement of gas under pressure past the combination contact and valve element 62 against compression spring 51. It will thus be seen that through this means, even though the aircraft is taken into the rarefied atmosphere, the transformer will be kept under pressure by the gases from the engine, and will be protected against leakage.

The diameter of hole 63 in the rod 60 is too small to permit flame propagation up into the rod. Moreover, after a few ignitions, the hole 63 contains sufficient products of combustion to inhibit a producing condition. Such pressure mixtures from the cylinder pass up through the hole 63 and then through a small gap 69, between the upper end of the insulator bodv 29 and the adjacent lower surface of the bottom flange 53 of the transformer supporting s ool, into the chamber 79 between the lock nut 5i and the lock nut 33. From that chamber 19, the pressure gases seen up into the upper chamber around the transformer and keep the atmosphere around the transformer at high pressure.

Due to the small unoccupied space inside of the enclosure there is very little capacity for the gases to fill.

The check valves 62 and spring 6! are set so that a firing stroke only will open the valve. At

this instant the gasoline vapor is or has been ig-. nited, so very little raw gas enters the opening in the end of the electrode. As the firing pres! sure drops in the engine cylinder, the check valve 62 will have closed and trapped ample pressure in the plug casing. If the plug is tight, the valve will remain closed most of the time, opening only to keep the pressure up in the casing.

With the high pressure in the plug, there is no danger from electric breakdown in the insulation. The low pressure input terminal H is made cone-shaped so that the inside pressure seals it tightly against the mating insulator cone 65.

The transformer is mounted on a ceramic spool, as described, and the secondary is wound next to the cone, with layers. The turns of primary and secondary are balanced for high frequency tuned circuit operation, and may be of fewer turns than are ordinary type ignition coils. A flux, guiding split shield 13 is placed preferably to encircle the entire transformer spool so that the coil fiux will take its path through the shield rather than induce eddy currents in the casing H5. The shield is substantially a cylinder with a longitudinal gap it to prevent eddy currents in the shield, and is preferably insulated from the enclosing shell I 5 by an insulating varnish or thin paper which is adequate for that purpose. The gap i i in the shield should preferably be oblique to its radius so the shield will provide a metal enclosure throughout the entire circular angle around the axis.

Simple electrical connections may be made to the upper input terminal H by means of a simple pressure disc 75 connected to the end of a wire conductor 15, leading from the ignition system and supported on an insulating disc plate ll that is secured to and supported by a pipe section '55 arranged to be tightly threaded onto the threaded head of the plug shell by means of a threaded nut 19.

By means of the construction illustrated herein a simple integrated spark plug is provided which can be simply and easily constructed and assembled to generate a high voltage directly at the spark plug where the high voltage is desired for use. The external ignition system necessary to excite the plug may, therefore, be completely of a low voltage system with a consequent elimination of need for highvoltage cables and insulating supports.

Moreover, the proper operation of the spark plug is assured by maintaining a locally pressurized atmosphere within each spark plug to prevent leakage that would result from a low pressure atmosphere.

This invention is not limited specifically to the exact details of construction that are shown since various simple modifications may be made therein without departing from the spirit and scope of the invention, as set forth in the ap pended claims.

What is claimed is:

l. A spark plug comprising a base supporting member adapted to be fitted into an engine head, an enclosing shell secured to the base member and having a low tension terminal at its upper end, a transformer having a contact engaging with the low tension terminal of the shell and having primary and secondary windings, the primary winding being connected at one end to the transformer contact, the other end of said primary being grounded along with one end of the secondary winding to the shell, a spool containing a magnetic core connected to the other end of the secondary winding connected to said magnetic core, a hollow insulating member and combined sealing and clamp means for securing said insulating member to said base supporting member, a rod extending through the insulating member having an enlarged opening in the upper end; said rod abutting the lower end of the transformer, a conductor compression spring within the enlarged opening of the upper end of the rod engaging at its upper end the core of the transformer, a metal contact element in said enlarged opening in the upper end of the rod and said conductor compression spring urging said contact into the bottom of the enlarged opening within the rod, and electrodes connected respectively to the lower end of the rod and to the base supporting member to provide a spark gap therebetween, said rod and the electrode thereon having a small hole communicating from the lower end of the electrode to the bottom of the large opening in the upper end of the rod whereby gas pressure from the engine may be delivered upwardly into the shell and about the transformer whereby to inhibit voltage leakage between turns of the windings and between the transformer and the shell and said contact element within the large opening in the rod being urged by the spring therein and serving as a valve element to withhold the gas within the transformer space under predetermined pressure and to allow the space to be replenished with gas pressure upon the gas entrapped therein being diminished.

2. A spark plug comprising a shell housing, a step-up transformer enclosed therein, an input terminal extending through the housing to supply low voltage to the transformer, a pair of spark gap terminals supported from the housing for insertion into the compression region of an engine cylinder, means for supplying high voltage from the transformer to the spark gap, and means for admitting pressure gases from a region in the neighborhood of the spark gap into 7 8 the housing to maintain a high pressure atmosphere around the transformer and within the housing during operation of the spark plug.

3. A spark plug, as in claim 2, in which the pressure admitting means consists of a oneway valve.

4. A spark plug, as in claim 2, comprising a metallic tubular conduit for electrically connecting the transformer secondary to one spark plug terminal and serving as the means for admitting and conducting the pressure gases from the region of said spark plug terminal into the housing to immerse the transformer.

5. A spark plug, as in claim 4, in which a oneway valve is disposed in the tubular conduit to control the admission of pressure gases into the housing.

6. In a spark plug having a pair of spark gap terminals and a transformer to be supplied with low voltage and to supply stepped up voltage to the spark gap terminals, and a housing for enclosing the transformer, the method of opera ing the plug while it is in service on an engine which comprises supplying pressure gases from the engine to the housing, to immerse the transformer in an atmosphere at a pressure higher than ambient pressure outside the plug.

7. The method set forth in claim 6 including the step of periodically replenishing the pressure upon any diminution by leakage from a predetermined pressure within the housing.

JAMES KENDALL DELANO.

REFERENCES CITED The following references are of record in the file of-this patent:

UNITED STATES PATENTS Number Name Date 2,266,614 Robinson Dec. 16, 1941 2,461,098 Weatherly Feb. 3, 1949 2,482,884 Tognola Sept. 27, 1949 2,575,140 Smith Nov. 13, 1951

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