US2347072A - Magnetic spark plug - Google Patents

Description

April 18, 1944. L. BEEH MAGNETIC SPARK PLUG Filed April 9. 1942 R. MH. N MM m w Bs E@ U O //W W /4 TTO/P/VEY Patented Apr. 18, 1944 UNITED STATES PATENT DFFICE MAGNETIC SPARK PLUG Louis Beeh, Long Meadow, Mass. Application April 9, 1942, Serial No. 438,256

8 Claims.

The present invention relates to spark plugs and more particularly to spark plugs for low tension ignition systems. The conventional high tension ignition systems operating with voltages as high as 25,000 volts had been developed as an improvement over the low tension systems used in the earlier years of internal combustion engines but abandoned because of the very high cost of the low voltage spark plugs used at that time, and which, furthermore, were not suited for engines operating with high compression. The high tension systems of present days, however, though satisfactorily operating at altitudes below about 25,000 feet frequently fail or break down at higher altitudes primarily due to the fact that the surface resistance of the conventional insulating materials vastly deteriorates with the decrease of the atmospheric pressure. The only remedy so far known against such failure of the insulation consists in an enlargement of the dimension whereby, however, other drawbacks, chieny an increase in weight and cost, are involved.

The present invention contemplates to overcome the mentioned drawbacks by providing a spark plug which is reliable and efficient in a low tension ignition system in order to make such system useful for modern internal combustion engines and particularly for those of aircraft reaching high altitudes. By employing a low tension system operating at a voltage of, e. g., only 100 volts, all or at least most of the diiiiculties can be avoided which are encountered in the conventional high tension systems.

However, although I mentioned hereinbefore a voltage of 100 volts, it is to be understood that I do not want to limit myself to any definite value, and that the invention is equally well applicable no matter whether the voltage employed is above or below 100 volts, it being sufficient that the voltage is considerably lower than that mentioned with respect to high tension systems.

Another object of the invention is to provide a low tension spark plug having satisfactory insulating properties up to any altitude which may be practically reached or is intended to be reached by aircraft.

Another object of the invention is to provide a spark plug in which the spark gap is controlled by electromagnetic means.

Still another object is the provision of a low tension spark plug which may be readily radio shielded, and whose interior may be completely closed against explosive gases so as to protect the spark plug from being overheated.

The invention consists of a spark plug mainly comprising means to create a magnetic field, a member .movable in response to the magnetic force of said field in one direction when said means is energized, and other means to restore said member to an original position when said first-mentioned means is de-energized, whereby a spark gap can be temporarily created between said movable member and a stationary spark plug body part which is exposed to the explosion gases when the spark plug is in use.

The invention further consists of a spark plug having a variable spark gap wherein one of the members between which the spark is created is movable in an axial direction and so formed similar to a valve as to prevent explosion gases from entering the interior of the spark plug body when the gap is closed.

Further objects and details of the invention will be apparent from the description given hereinafter and the accompanying drawing illustrating an embodiment thereof by way of example. In the drawing:

Fig. 1 is a longitudinal cross-section of a spark plug according to the invention.

Fig. 2 is a top plan View of a leaf spring constituting a. part of the spark plug of Fig. 1.

Figs. 2a and 2b are similar views of modifications of the spring shown in Fig. 2.

Fig. 3 is a longitudinal cross-section of a modied spark plug, and

Fig. 4 is a digrammatical illustration of a low tension ignition circuit comprising a spark plug according to the invention and the means for energizing the same.

Referring now to the drawing, the spark plug of Fig. 1 comprises a body I0 of magnetizable metal substantially shaped as a hollow cylinder II with a bottom I2, an interior axial projection I3 and an exterior lower portion I4. Portion I4 is preferably so dimensioned and threaded at I5 that it can be screwed into the conventional or standard tapped spark plug hole of a cylinder of an internal combustion engine not shown by applying a wrench to the hexagonal portion II' of the cylinder I I. An insulating spool I6, e. g., of ceramic material, is inserted into the cylinder II so as to surround the tubular projection I3 and to bear with a lower flange II on the cylinder bottom I2. Spool I6 is provided with an upper flange I8 forming the top cover of the cylinder II and being recessed at I9 to receive in said recess a gasket 20 which is interpositioned between the flange I8 and the top rim of the cylinder I I. For a purpose to be hereinafter explained, the flange I8 has an upwardly projecting rim 2| with an interior is arranged on spool |5.in the chamber formed by the inner wall of the cylinder I I, and the spool I6 with its flanges I1 and I8. The ends 24 and 25 of the coil 23 are passed through holes 26 and 21 respectively in flange I8. The end 24 is connected to a leaf spring 28 which rests on the afore-mentioned rim shoulder 22. The spring as shown in Fig. 2 is preferably shaped with a peripheral ring portion 29 and a central portion 30 connected with each other by armor spoke-like portions 3| and provided with a hole 32. Springs of other shape, such as, e. g., illustrated in Figs. 2a and 2b, may be used instead of spring 28. The springs 28 and 28" differ mainly in the manner in which the arms 3| and 3| are arranged in relation to the respective rims 29' and 29" and centers 30' and 30".

On top of the peripheral portion of spring 28 a ring 33 is placed which is of insulating material as, for instance, of mica. A dome-shaped terminal member 34 bears with` its flange 35 on the ring 33, and the arrangement ls such that the upper face of flange 35 and the upper edge of rim 2| are substantially flush when the parts are assembled as shown in Fig. 1. The end 25 of coil 23 is connected to terminal member 34 which has a top projection 36 suitably shaped for the attachment of an ignition cable not shown. Another insulating ring or gasket 31 of greater width than 33 is placed on the top of rim 2| and flange 35, and a metal cap 38 bears with an interior shoulder 39 on ring 31 so as to hold the parts in assembled position. The cap 38 also serving as a radio shield has a lower cylindrical extension 40 which fits over the rim 2| and the top portion of the body cylinder II and is secured by its indented rim 4| engaging in a peripheral groove 42 of the cylinder I I. The top portion 43 of cap 38 ls tubular and provided with a threading 44 for the attachment of a xture 45 or the like for the afore-mentioned ignition cable.

It will be noticed that the tubular projection I3 does not extend upwardly all the way through the length of the spool I6, and that there is a free space 46 interiorly of said spool above the projection I3. In this space, a soft iron core 41 engages which is attached to the spring 28 by means of a pin 48 and nut 49 and which can move in axial direction as far as spring 28 allows. Pin 48 extends downwardly through the entire length of the spark plug body I in a central bore 50 of the latter, and has a diameter so much smaller than that of said bore 50 that no sparks can occur insulating material inserted in the lower projection I4 of body I0. A contact ring 52 of suitable material is inserted in the lower face of projection I4, and the lower end of pin 48 is provided with a head or flange 53 which bears on ring 52 when core 41 and pin 48 are in their topmost position under the action of spring 28 as shown in Fig. l. Now it will be clear that the close fit between pin 48 and bushing 5I prevents explosion gases from entering the interior of the spark plug and that the parts 53 and 52 between which the ignition spark will occur in operation act like a valve or an additional means for withholding such gases from the interior of the spark plug when part 53 is urged against ring 52.

If the spark plug body is grounded by screwing it, e. g., in the spark plug hole of a cylinder of an internal combustion engine, and if, then, current is supplied from a. source by a, cable attached to the portion 36 of part 34, the current will oW through coil 23 from its end 25 to its end 24, through spring 28, core 41, pin 48, flange 53, ring 52, body projection I4 to ground. Thereby a magnetic fleld is set up with the effect that core 41 with pin 48 will be pulled downward against the restraint of spring 28. A gap will be created between flange 53 and ring 52 so that sparks will pass from the one to the other to ignite a surrounding explosive gas mixture. When the current is interrupted the magnetic flux will stop and the core 41 with pin 48 will be returned by spring 28 to their original position in which the parts 52 and 53 contact each other, so that a subsequent current impulse can rebuild the magnetic field and cause the occurrence of ignition sparks as hereinbefore described. It will be noticed that the spark plug according to the invention has certain self-adjusting qualities. On the one hand, the force of the magnetic field is a function of the current flowing through coil 23 from end 24 to 25. The greater the current flow, the deeper will core 41 be pulled into the spool and the larger will be the gap between the parts .52 and 53. The closer the core 41 is to the tubular projection I3, the greater will be the magnetic forcebut at the same time, the greater will be the deflection of the spring 28, and the stronger will be its force resisting the downward movement of the core, and the larger the gap between ring 52 and 53, the larger will be the drop in current flow between these two parts with the effect that less of the total current is available to energize the magnetic field. Hence, the spark plug is operative within reasonably wide limits of variation of the voltage for which it is destined. Furthermore, it will be noticed that the magnetic force will be a maximum when' the contact 53 is in its topmost position. At the same time the force of the spring is a minimumas the latter is not or only very little deflected. Hence, the difference of the two forces will also be a, maximum. 'Ihis maximum i is helpful in overcoming the load on the contact 53 owing to the compression prevailing at the time of ignition in the motor cylinder to which the spark plug is applied. As soon as the gap is slightly opened the major portion of such compression load will disappear.

In the modification illustrated in Fig. 3, a coil spring is used instead of the leaf spring 28, and parts are differently shaped and arranged from the preferred embodiment shown in Fig. 1. In Fig. 3, the spark plug body IIO of magnetizahle material comprises a hollow cylindrical portion III with a lower projection II4 provided with the external threading I I5 whereby the plug can be secured to a cylinder of an engine. The projection II4 is hollow so that its interior space II3 constitutes a restricted continuation of the cylinder chamber |I2. An interior ring-shaped shoulder IIB is provided in the lowest portion of projection II4. The space I I3 is occupied by a tubular guide member II1 of insulating material, such as a ceramic, which bears on the shoulder IIE and has an upper flange II8 resting on the ring-shaped bottom surface IIS of cylinder III. Member II1 has a circular recess in its upper face to receive therein a washer |20 of conductive material. On top of flange II8 and washer |20 rests a spool I2I similar as to purpose and shape to the spool I6 of Fig. 1; and a gasket ring |22 is provided between the upper flange |23 of the spool and the upper rim of the cylinder III,

The spool |2| carries between its upper flange |23 and its lower flange |24 a wire coil |25 as described with respect to the coil 23 of Fig. 1. The

upper flange |23 is recessed in its top surface at |26 so as to receive in said recess a terminal member |21 having a vent hole |28 and an upper extension |29 which constitutes a. terminal for the attachment of a cable not shown. Between the member |21 and a. shoulder |30 of spool 2|, a screen |3| and a gasket ring |32 are inserted. An insulating ring |35 preferably of mica is placed on top of the flange |23 and part of the member |21 and held in position by the internally projecting flange |33 of a tubular metal member |34 which incloses the upper portion of cylinder III and is secured thereto in a manner similar to that applied in the connection of member 40 to cylinder in Fig. 1. The two ends |36 and |31 of the spool |25 are passed through holes in the flanges |23 and |24 and connected to member |21 and washer` |20 respectively. The central holev |38 of this washer |20 is smaller than the cross-section of the interior space |39 of spool |2| so that it constitutes an inwardly projecting rim which supports a coil spring |40 arranged in the space |39. The upper end of the spring bears against a soft iron core |4| axially movable within the upper portion of the space |39. A pin |42 is screwed into the core at |43 and secured in position by a, split ring or the like |44. The pin extends through the spring |40 and an axial bore |45 of the member ||1 in which it is axially movable with a close iit similar to pin 48 in bushing 5| of Fig. 1. The pin is provided at its lower end with a flange or head |46 bearing, under the action of spring |40, against a contact ring |41 inserted into the lower face of the body portion ||4, similar to the arrangement of the parts 52 and 53 in Fig. 1.v

Now, it will be clear that the modified spark plug operates in practically the same manner as that of Fig- 1. If the portion ||4 is grounded, and a cable attached to the top projection |29 of member |21, current can pass from said member through coil end |36 into the coil |25 proper, from there through the end |31, washer |20, spring |40, core |4|, pin |42, pin head |46, contact ring |41, and body portion ||4 to ground. The current in coil |25 sets up a magnetic field which pulls the core 4| downward against the restraint of spring |40 thereby opening a spark gap between the pin head |46 and contact ring |41. When the current is interrupt spring |40 restores the core and pin to their original position. i

A low tension ignition circuit suitable to supply adequate low tension current to spark plugs of the type described will be explained with reference to the diagram of Fig. 4. In this figure, a magneto 60 comprises a rst permanent magnet 6| with pole shoes 62 and 63 and a second permanent magnet 64 with pole shoes 65 and 66. A cross shaped rotor 61 of soft iron can rotate between the four pole shoes, and the latter are so arranged that when an arm of the rotor cross is in front of one of the shoes of one magnet the diametrically opposite arm is also in front of that shoe of the other magnet which has the opposite polarity; e. g., if upon rotation of the rotor the arm 68 is in front of the shoe 62 which has negative polarity, the arm 69 will be in front of the shoe B which is a positive pole. The magneto further comprises a soft iron core bridging one of the poles of the one magnet and the pole of the same polarity of the other magnet.

in Fig. 4 the core 10' bridges the two negative magnet poles 62 and 65. Hence, when the rotor is in a position as hereinbefore mentioned, in which rotor cross arm 68 is in front of pole shoe 62 a magnetic flux will take place from the positive pole of magnet 64 through rotor cross arms 69 and 68, polepiece 62, core 10 and to the negative side of magnet 64. If, however, upon further rotation a pair of opposite rotoxarms is in front of the pole shoes 63 and 65 the magnetic ux through the core 10 goes in the other direction, reversal taking place whenever the rotor cross is in the position of Fig. 4 in relation to the pole shoes 62, 63, 65 and 66. Core 10 is provided with a primary winding 1| of relatively thick wire and small number of turns and a secondary winding 12 of thinner wire and a greater number of turns. The one end 13 of the primary windingris grounded at 14 and its other end is connected at 15 with one end of the secondary wind- I ing 12. The free end 16 of the latter is connected Thus,

'tact breaker 82.

via a distributor 11 by a wire 18 to the coil 19 of a spark plug according to the invention, coil 19 corresponding to coil 23 in Fig. 1 or |25 in Fig. 3, and being grounded at through the spark plug body as hereinbefore described. The distributor 11 is of a type conventional in the ignition system of a multi-cylinder engine. A condenser 8| and a breaker 82 are connected in parallel to the primary winding 1| and, hence, also in parallel to the circuit comprising the secondary winding 16, the distributor 11 and the spark plug coil 19. The breaker 82 is so connected to the rotor 61 by mechanical means indicated by the dot and dash line 83 that the current through the primary winding 1| will be shortly broken each time and at exactly the moment when the magnetic flux is reversed.

The system operates as follows: When the soft iron rotor 61 is rotated in the magnetic eld, the magnetic flux flowing through the soft iron core 10 will induce a current in the windings 1| and 12. At the moment of the ux reversal as hereinbefore described, the current flowing in the primary winding 1.| is interrupted by the con- This reversal and break raises the induction in the secondary winding 'I2 to its maximum. Since the end 16 of the secondary winding is connected to the spark plug, in fact to the member 34 in Fig. 1 or to member |21 in Fig. 3, the secondary current flows through the spark plug coil 19 (i. e., 23 in Fig. l or |25 in Fig. 3) where it induces the magnetic field formed by the spark plug body and attracts the iron core 41 of Fig. 1 or |4| of Fig. 3, thereby causing a break between the head of the contact pin and the contact material mounted on the spark plug body. This break creates an arc or spark which is of an oscillatory nature and high in heat value due to the fact that the condenser 8| of the system is connected parallel to the secondary winding 12 and coil 19 in series as well as to the primary winding 1|.

The system has the following advantages over Y the conventional high tension system. The low voltage current is easily insulated on the magneto and distributor for high altitude iiying. It permits proper insulation of the spark plug which at present is limited to about 30,000 feet altitude. The low voltage system is more easily manufactured because of the elimination of high voltage difculties in production. All its elements including the spark plugs are more easily radio shielded than those of a high voltage system. The interior of the spark plug according to the invention is completely closed against explosion gases, thereby eliminating overheating. The elements of the low voltage system are lower in production cost and labor, and the magneto required in the low voltage system is not in excess of the outside dimensions and weight compared with the high tension magneto, and the distribution and timing of the spark does not involve other than conventional elements. The low voltage system and particularly the spark plug according to the invention is less sensitive in operation than the corresponding elements of the conventional high voltage system.

It will be understood that various changes in the specic form of my novel spark plug may be made without departing from my invention which is not limited by the particular disclosure of the embodiments thereof illustrated and described hereinabove but by the scope of the appended claims.

I claim:

1. A spark plug comprising a body of magnetizable metal including a hollow cylindrical upper portion and an exteriorly threaded lower portion provided with an axial bore in continuation of the interior of said cylindrical portion, a rst contact element in connection with the bottom face of said lower portion, an insulated coil in said cylindrical portion, a core member in coaxial arrangement with the coil and movable in one axial direction with respect thereto when the coil is energized, a second movable contact element so arranged and constructed as to cover the bottom entrance of said bore when contacting said first contact element and including an axial pin connecting said second element to said core through said bore, a spring insulatedly secured to said cylindrical portion and conductively connected to the one end of said coil, said spring being in engagement with said core and tending to move it in the opposite direction so as to hold said elements engaged, and means to connect the other end of said coil to an external current source.

2. A spark plug as claimed in claim 1, Whereil said rst contact element is a ring attached to the bottom face of said lower bottom portion, and said second contact element -is.\constituted by a substantially flange-shaped head of the lower end of said pin.

3. A spark plug comprising a body of magnetizable material including a, hollow cylindrical upper portion open at its top, a tubular projection interiorly of said cylinder and extending axially upward from the cylinder bottom, and a lower exteriorly threaded portion with an axial bore in continuation of that of said tubular projection, a spool of insulating material interiorly of said cylinder and encompassing said projection, said spool having a top flange covering said cylinder, a spring attached to said flange, a coil on said spool, a core carried by said spring in an axial space of said spool above said projection, a first contact element attached to the bottom face of said lower portion, a second contact element including a pin passed through said bore and connected to said core, and insulating and sealing means between said pin and the wall of said bore, whereby gases are substantially prevented from entering said body.

4. A spark plug as claimed in claim 3, wherein said spring is substantially wheel-shaped including a fellow-like rim portion supported by said spool flange, a hub-like center portion to which said core is attached, and spoke-like portions connecting said rim to said center portion.

5. A spark plug comprising a body of magnetizable material including an upper portion and a lower portion, said portions constituting communicating cylindrical chambers, each with an interior annular shoulder at its bottom, said lower portion and chamber being narrower than the upper and being exteriorly threaded, a tubular insulating member including a top flange interiorly of said lower chamber and with said iiange covering the shoulder of said upper chamber, an insulating spool interiorly of said upper chamber, said spool including a lower and an upper flange and being provided with an axial hollow space, said lower flange being arranged above said ange of said member and said upper flange on top of the rim of said upper portion, a coil on said spool, a helical spring interiorly of said spool and conductively connected to the one end of said coil, a core interiorly of said spool and bearing on said spring, means for' connecting an external current source to the other end of said coil, a contact means in connection with the bottom face of said lower portion, and a movable contact in cooperative relation to said contact means and connected to said core so as to respond to the movement of the core owing to magnetic attraction and the restraint ci' said spring, said movable contact including a portion slidingly tting in salu tubular member so as to substantially prevent gases from entering said body.

6. A spark plug comprising a body including a hollow cylindrical upper portion and a, lower portion adapted to be connected to the combustion chamber of an internal combustion engine, a coil interiorly of said body and provided with an axial hollow space, a core projecting into said space from the top so as to be attracted by a magnetic force in axial direction when said coil ls energized, a spring in engagement with said core and tending to raise it, a rst stationary contact element attached to the bottom face of said lower portion, a second contact element movable with respect to said first element and including a pin-like member in connection with said core and in axial arrangement with respect to said cylindrical portion, and means for guiding said pin substantially gas tight in said lower portion.

7. A spark plug as claimed in claim 6, wherein said rst contact element is ring-shaped and said second element is shaped as a bottom iiange of said pin so that the two elements, in valvelike manner, prevent gases from entering the interior of the spark plugr when the elements contact each other.

8. A magnetic spark plug comprising a hollow body having an axial bore through its lower portion, an electric coil and a movable core interiorly of said body, a stationary contact at the bottom of and coaxial with said bore, a bushing of insulating material in the lower portion of said bore, a movable Contact member slidably fitting in said bushing so as to substantially prevent the entrance of gases into said body from below, said member being responsive to the core movement and including a lower enlarged portion tting on said stationary contact so as to cover the lower end of said bore when said movable contact, in an end position, engages said stationary contact.

LOUIS BEEH.

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