US2380707A

US2380707A - Ignition means

Info

Publication number: US2380707A
Application number: US486723A
Authority: US
Inventors: Marc C Sawyer
Original assignee: Bendix Aviation Corp
Current assignee: Bendix Aviation Corp
Priority date: 1943-05-12
Filing date: 1943-05-12
Publication date: 1945-07-31
Anticipated expiration: 1962-07-31

Description

M. C. SAWYER IGNITION MEANS July 31, 1945.

Filed May 12, 1945 FIG.1

T0 DISTRIBUTOR D /5 INVENTOR.

ATTORNEY FIG. 2

- Patented July 31, 1945 IGNITION MEANS Mare 0. Sawyer, Otsego County, N. Y., assignor to Bendix Aviation Corporation, New a corporation of Delaware York, N. Y.,

Application May 12, 1943. Serial a... 488,723

s Claims.

This invention relates to ignition means for internal combustion engines and more particularly to an ignition system adapted for use as a socalled booster for starting the engine.

One of the objects of the present invention is to provide a novel ignition system for. an internal combustion engine wherein the electrical ener y for firing the spark plugs is developed in a novel manner.

Another object of the invention is to provide a novel ignition system for an engine which is particularly adapted for low tension distribution of the electrical current to the spark plug circuits.

A further object is to provide a novel ignition circuit which is particularly adapted for use in starting internal combustion engines.

Still another object is to provide an ignition system wherein a booster or starting circuit is novelly combined with a conventional ignition system.

Another object is to provide a novel ignition system of the above character whereby a minimum amount of wiringisrequired.

A still further object is to provide a novel booster coil unit for use in coniunction'with the ignition system of an internal combustion engine.

The above and further 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 only and is not intended as a definition of the limits of the invention, reference for this lattel'iggrpose being primarily had to the appended cla In the drawing, wherein like reference numerals refer to like parts throughout the several views,

1 is a. diagrammatic view illustrating one type of ignition system embodying the features of the present invention;

Fig. 2 is a similar view showing a modification of the system of Fig. 1; and,

magneto 5 which embodies a ma netic rotor 8 adapted to cooperate with stator poles 1 which are in turn connected by a core 8 on which a coil 0 is wound. Upon rotation of rotor 6, such as by the engine, alternating current at relatively low voltage is generated in coil 9 in a manner well understood in the art. I

One end of coil 9 is preferably grounded at Illa and the other end thereof is connected by a lead II to one contact of a circuit breaker I i the other contact of which is also grounded at Illa or otherwise. The contacts of circuit breaker II are normally urged to engaged or closed position by suitable resilient means (not shown) and are periodically moved out of engagement with each other or to open position by a rotatable cam I! which may also be driven by the engine. Cam l2 may be of any suitable design but, if the ignition system is used on a radial engine, the cam is preferably of the compensated type having a lobe for each cyclinder 01' the engine, said lobes being spaced to properly time the sparks in each cylinder. A condenser i3 is preferably connected across the terminals of circuit breaker II to prevent arcing when the contacts are separated.

The insulated or ungrounded terminal of circuit breaker i l is connected to a suitable distributor D which may take the form Many of many wellknown designs. In the form shown, the distributor comprises a stationary insulated ring it, to which circuit breaker I i is connected by means of 'a lead II, and a plurality of arcuate circularly arranged insulated contacts i6. Current delivered to ring it by the magneto or other suitable source Fig. 3 is a similar view showing a second modi fication of the booster circuit.

In the limited numberv oi embodiments illustrated in the drawing, the features of the invention are shown, by way of example, as being embodied in an ignition system for a 9-cylinder engine wherein the electricalcurrent is distributed at low voltage, the voltage being stepped upat a transformer or spark coil near each spark plug for the purpose of creating the necessary ignition spark. In the form shown, the main ignition current for normal operation is generated by a is picked up by a carbon or similar brush I I carried-by a rotating distributor finger l8 andconducted to contacts l6 through a brush it which is also carried by said finger and electrically connected with brush I! by .a conductor 20. Distributor finger it may be rotated by the-engine in timed relation with cam-l2 and magneto rotor 6.

Each of the distributor contacts I6 is connected through a lead 2| to the primary winding 22 of a spark coil, which winding is in turn connected to ground at 23. By controlling the flow oi electrical current at relatively low voltage to coil windignition switch 28, the "oil" terminal of which is connected by a lead 21 to said coil. The movable element 28 oi. the ignition switch may be grounded at 2! in any suitable manner.

In thevcperation of the ignition system thus is: described, with ignition switch 28 in on position, the contacts of circuit breaker] l are held in closed position during the build up of current in coil 2 of the magneto-generator. Each time the current in coil 8 approaches its maximum value, the points oi circuit breaker H are openedby the lobes of cam l2, whereupon the current from the coil must flow through lead II and distributor D in the manner fully described above to a spark coil primary winding 22. Thi sudden surge of current through winding 22 is effective to induce the necessary energy in the secondary circuit, which includes winding 24, to create a spark at spark plug gap 25. As distributor finger It moves brush it over the contacts II, the spark plugs of the engine are successively fired in a predetermined order, the, timing of each spark being determined by the openingof circuit breaker ii.

In an ignition system of the above character, it is highly desirable to provide an electrical resistance in the primary circuit which is 01' suiiicie'nt during operation or the booster coil unit 3|. In

the primary windings 22 of the transformer coils,

thereby making it possibleto use smaller wire and reduce the size oi these coils. In one satisfactory embodiment o! the invention, a resist-- ance of 16 ohms in each primary winding 22 has been found suitable. This resistance value may differ, however, with different installations-the most suitable value may be determined by resorting to oscillograph or like measuring means for determining the characteristics of the current in the primary circuit. The resistance may be incorporated in the primary circuit at any to produce the desired dissipation oi the residual ener y.

Since rotor 8 is driven by the engine, sumcient energy cannot be generated by magneto I to start theengine when the crankshaft oi the latter is turned slowly by the starting motor. Novel means which are independent of the speed or the engine are accordingly provided for generating the 11 starting energy. In the form shown, said novel means comprises a novel buzzer type booster coil unit 2| which includes a coil 2| having relatively high inductance wound on a core 32. coil II is adapted to be connected in circuit with a battery 33 or other suitable source of current, a starter operated switch 24 and buzzer contacts 2|. across which a condenser 2| may be connected to prevent arcing. One oi the buzzer contacts is mounted on a pivoted arm 21 which is normally urged toward a contact closing position by a spring 38 or other suitable resilient means and which is adapted to be electromagnetically moved to contact open position when coil II is energized. A current limiting ruse 39 may be provided in the circuit between buzzer contacts 28 and coil II to obviate any danger oi burning out the coil it said contacts should stick in closed position. The other end of coil 3| assoao-r may be connected to ground at 29 through the on" position terminal of ignition switch 28 and switch lever 22.

If the booster sparks can be permitted the same advance as the magneto sparks during normal operation or the engine, or if suitable automatic or manual means are provided for retarding the timing of the magneto to the engine for starting purposes, booster coil ll may be directly connected to the input terminal [4 of the distributor so that the required timing might be eil'ected by main circuit breaker I I. In this case, the timing would be eflected by the opening of the main circuit breaker since the current from the booster will flow to ground through said breaker when the latter is closed and to the distributor when the breaker points are open. In most installations it is desirable to provide separate means for retarding the booster spark and this may be done by employing a second circuit breaker 40 connected between coil II and distributor ring it Breaker ll may be operated by cam l2 or a second cam may be provided for this purpose.

A resistance 4| is preferably provided in the connection 42 between the boostercoil' or inductance coil II and the main ignition circuit to limit the current which may flow from the booster coil unit through magneto coil 9. The current which ilows in this manner through the latter coil must be maintained sufliciently small to prevent any material demagnetization of magnet t. Resistance ll also prevents a dead short circuit when both of the circuit breakers II and ll are closed onevsuitable embodiment of the invention, resistance 4| has a value or approximately 3 ohms and the inductance of coil 3| is amroximately 5 milli-henries but these values may vary with the characteristics orathe magneto which said re- 'sistance protects, the resistance in the primary circuit and other characteristics of the system.

' The required value of resistance II to avoid undue circuit under all possible conditions of operation desired point and should only be sumciently large The value 01' the inductance 4| must be large enough to properly energize

coils

22, 24 under operating conditions and hence depends on the characteristics and requirements of the system.

- rent will then how from battery 23 through contacts 88, coil 3! and switch 28 to ground at 2!. Upon excitation or energization oi electromagnet ll, 32 in this manner, the buzzer contacts II are electromagnetically opened, thereby breaking the circuit to coil 2| so'that said contacts will be closed again under the action of spring 28. This cycle of operation of the buzzer contacts is repeated again and again in rapid succession, as is well understood in the art.

During operational. the booster coil or busaer as above described, circuitbreaker ll isperiodically opened by cam l2. The relative positions of cam l2 and circuit breakers II and ll are such that a few degrees of rotation of the cam Y aseonov While the booster unit is operating with the parts in the last mentioned positions, 1. e. with circuit breaker ll open and circuit breaker 4| closed, a

self-induced current flows in surges from coil 3| to the distributor D through lead I! and, hence. to one of the spark coils 22, 24. A surge of current to the distributor and, hence, to a spark coll occurs each time buzzer contacts 36 are moved to open position. This current which -is used in the creation of the sparks at spark plugs 23 for starting the engine is induced in booster coil 3| by the sudden collapse of the magnetic field which is built up around the coil when current from battery 33 is permitted to flow therethrough to ground. The inductance of coil 3| is made suinciently high so that the transient voltage which is developed across said coil when contacts 33 are opened is sufficient to produce good booster sparks at spark plugs 23 in spite of the relatively high ohmic resistance of each primary winding 22 or other resistance provided in the primary circuit for thesame reasons.

When the engine starts, 1. e., when rotor 6 is turned sufliciently fast by the engine to produce the necessary current to operate the engine without the assistance of the booster coil unit, starter switch 24 may be opened automatically or otherwise by any of many suitable means well-known in the art. The operation of the booster coil unit will thus be stopped during normal operation of the engine.

In one embodiment of the invention which proved highly successful on a nine cylinder aircraft engine, a battery rated at 24 volts was employed and a 20 ampere current limiting fuse 39 was used. Condenser 36 had a value of .25 microfarad, the resistance of coil 3| was approximately one ohm and the inductance of said coil was approximately milli-henries. In this same embodiment, the value of resistance 4| was approximately 3 ohms and the resistance of each of the primary windings 22 was 16 ohms, as heretofore pointed out.

In the modification of Fig. 2, the booster circuit breaker 40 is eliminated and the main circuit breaker I l is employed for timing the booster impulses. In place of the booster circuit breaker, a suitable switch 44 is provided for cutting the booster circuit out of the system during normal operation of the engine to thereby prevent the booster from short-circuiting the magneto impulses. In all other respects the embodiments of Figs. 1 and 2 are the same. In operation, when ignition switch 26 is in "on position and switches 34 and 44 are closed, the self-induced impulses from booster coil 3| upon opening of points 35 will flow to the distributor and, hence, to the spark coils 22, 24 only when circuit breaker H is in open position. When this circuit breaker is closed the current will flow across the points thereof and to ground at Illa. Accordingly, the timing of the initial booster spark in each engine cylinder is determined by the opening of circuit breaker II. If desired, some suitable means known to the art may be employed for retarding the opening of circuit breaker I l during the starting operation.

The embodiment illustrated in Fig. 3 is the same 3 held in open position by suitable resilient means,

such as a coil spring 41 attached to arm 48. The

latter is attracted by solenoid 3|, 32 when the booster is in operation tothcreby close the circuit at points 46 and permit the booster impulses to flow to the primary or distributor circuit. The operation is the same as described above in connection with Fig. 2 except for the automatic operation of cut-out switch 45.

Any well known method may be employed for insuring continued closure of switch 45 whenever buzzer contacts 35 are in operation. For example, armature 46 may be made heavier than arm 31 and/ or spring 41 may be made lighter than spring 33. To provide ample insurance against any undesired opening of contacts 45 when spring 41 is made sufliciently strong to avoid any undesired closing 01 said contacts as a result of vibration or other cause during engine operation, a socalled flux catcher 48 may be provided. Element 48 concentrates the magnetic flux acting on armature 46 and hence prevents the opening of con- "tacts 45 each time contacts 35 are opened even though spring 41 may be relatively strong. The eilfectiveness of means 48 may be increased by placing a shorted turn of copper wire 49 thereon to provide a shaded pole effect, as is well understood in the art.

There is thus provided a novel ignition circuit for an internal combustion engine wherein the electrical current delivered to the primary winding of a transformer or spark coil is produced in a novel and simplified manner. There is also provided an ignition circuit equipped with a booster for starting purposes wherein the wiring for the switch means is reduced to a minimum. Novel means are also incorporated in a low voltage distribution ignition system for supplying a starting current in properly timed surges to the primary'windings of spark coils for inducing high tension current in the secondary windings of said coils. Additionally, the system provided by the present invention is also operable equally well at all altitudes.

Although only a limited number of embodiments of the invention have been diagrammatically illustrated in the drawing, it is to be expressly understood that changes in the details thereof may be made without departing from the spirit and scope of the invention. For example, many different types of distributors may be employed, the necessary resistances may be inserted at different points than illustrated and described, the resistances may be either concentrated in resistance units or distributed in leads where the same are required or desired, and the values of the various resistances, voltages, etc., may be variedito advantage in systems having different characteristics. Other changes which do not depart from the spirit and scope of the invention will also be apparent to persons 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 ignition apparatus, electrical currentgenerating means including a coil and magnetic means for inducing alternating current therein, a first circuit breaker connected across said coil, means for normally holding said circuit breaker in closed position, means for periodically opening said circuit breaker in timed relation with the operation of said magnetic means, a transformer coil having primary and secondary windings, means for grounding said coils, means connecting the ungrounded side of said circuit breaker to the ungrounded end of said primary winding, a condenser connected in parallel with said circuit breaker, a spark gap in series with said secondary winding, whereby a surge of electrical current flows through said primary winding to creat a spark at said gap when said circuit breaker is opened, a source of uni-directional electrical current, a second circuit breaker having one side thereof connected to the ungrounded terminal of said source, means for normally holding said second circuit breaker in closed position, a self inductioncoil having the ungrounded end thereof connected to the other side of said second circuit breaker, said induction coil being adapted to electromagnetically open said second circuit breaker when energized by said source, a condenser connected in parallel with said second circuit breaker, a current limiting fuse connected in the circuit between said source and said induction coil, a resistance having one end thereof connected to the ungrounded end of said induction coil, a third circuit breaker having one side thereof connected to the other end of said resistance, means connecting the other side of said third circuit breaker to the ungrounded side of said first circuit breaker, and means for periodically closing said third circuit breaker when said first circuit breaker is in open position.

2. An ignition system comprising a main circuit including a source of electrical current, a circuit breaker through which current from said source normally flows, a condenser connected in parallel with said circuit breaker, means for periodically opening said circuit breaker, current distributing means having an input terminal to which current from said source fiows when said circuit breaker is in open position and a plurality of ignition coils having the primary windings thereof connected to the output terminals of said distributor means for successive connection to said source, an auxiliary circuit comprising a second source of electrical current, a buzzer including a self induction coil connected with said second source and means connecting one end of said coil to ground, and

means connecting the other end or said coil to the input terminal of said distributor.

3. An ignition system comprising a main circuit including a source of electrical current, a circuit breaker through which current from said source normally flows, a condenser connected in parallel with said circuit breaker, means for periodically opening said circuit breaker, current distributing means having an input terminal to which current from said source flows when said circuit breaker is in open position and a plurality of ignition coils having the primary windings thereof connected to the output terminals of said distributor mean for successive connection to said source, an auxiliary circuit comprising a second source of electrical current, a buzzer including a self induction coil connected with said second source and means connecting one end of said coil to ground, means connecting the other end of said coil to the input terminal of said distributor, a circuit breaker in said last-named connecting means, and means for periodically closing said last-named circuit breaker while said first-named circuit breaker is in open position.

4. In an ignition system, a main circuit comprising a source of alternating electrical current including an induction coil, a circuit breaker through which said current normally flows, a condenser connected in parallel with said circuit breaker, a transformer having primary and secondary windings, means connecting said primary winding to the ungrounded side of said circuit breaker and means for periodically opening said circuit breaker whereby a surge of current is caused to flow through said primary winding, an auxiliary circuit comprising a source of unidirectional electrical current, an inductance connected across said last-named source and a pair or buzzer contacts connected between said last-named source and the high potential end of said inductance, said buzzer contacts being operable to open position by the magnetic fleld of said inductance, and means for connecting the high potential end of said inductance to the ungrounded side of said circuit breaker.

5. In an ignition system, a main circuit comprising a source of alternating electrical current including an induction coil, a circuit breaker through which said current normaly flows, a condenser connected in parallel with said circuit breaker, a transformer having primary and secondary windings, means connecting said primary winding to the ungrounded side of said circuit breaker and means for periodically opening said circuit breaker whereby a surge of current is caused to fiow through said primar winding, an auxiliary circuit comprising a source of unidirectional electrical current, an inductance connected across said last-named source and a pair of buzzer contacts connected between said last-named source and the high potential end of said inductance, said buzzer contacts being operable to open position by the magnetic field of said inductance, means for connecting the high potential end of said inductance to the ungrounded side of said circuit breaker, a circuit breaker in said lastnamed connecting means, and means for periodically closing said last-named circuit breaker while said first-named circuit breaker is in open position.

6. An ignition system comprising a main circuit including a source of electrical current, a circuit breaker through which current from said source normally fiows, a condenser connected in parallel with said circuit breaker, means for periodically opening said circuit breaker, current distributing means having an input terminal to which current from said source flows when said circuit breaker is in open position and a plurality of ignition coils having the primary windings thereof connected to the output terminals of said distributor means for successive connection to said source, an auxiliary circuit comprising a second source of electrical current, a buzzer including an induction coil connected with said second source and means connecting one end of said coil to ground, means connecting the other end of said coil to the input terminal of said distributor, and a cutout switch for disconnecting saidauxiliary circuit from said main circuit.

'1. In an ignition system, a main circuit comprising a source of alternating electrical current including an induction coil, a circuit breaker through which said current normally flows, a condenser connected in parallel with said circuit breaker, a transformer having primary and secondary windings, means connecting said primary winding to the ungrounded side of said circuit breaker and means for periodically opening said circuit breaker whereby a surge of current is caused to fiow through said primary winding, an auxiliary circuit comprising a source of unidirectional electrical current, an inductance connectedacross said last-named source and a pair of buzzer contacts connected between said lastnamed source and the high potential end of said inductance, said buzzer contacts being operable to open position by the magnetic field of said inductance, means for connecting the high potential end of said inductance to the ungrounded side of said circuit breaker, circuit breaker means for disconnecting said auxiliary circuit from said main circuit,.yieldable means for normally holding said circuit breaker means in open position, and electromagnetic means for holding said circuit breaker means in closed position during op-- eration of said buzzer contacts.

8. An ignition system comprising a main' circuit including a source of electrical current, a circuit breaker through which current from said source normally flows, a condenser connected in parallel with said circuit breaker, means for periodically opening said circuit breaker, current distributing means having an input terminal to which current from said source flows when said circuit breaker is in open position and a plurality of ignition coils having the primary windings thereof connected to the output terminals of said distributor means for successive connection to said source, an auxiliary circuit comprising a second source of electrical current, a buzzer including an induction coil connected with said second source and means connecting one end of said coil to ground, means connecting the other end of said coil to the input terminal of said distributor, circuit breaker means in said lastnamed connecting means, means for normally holding said circuit breaker means in open position, and electromagnetic means including said induction coil for closing said circuit breaker means when said buzzer contacts are in operation.

9. The method of creating sparks across the gap of a spark plug in an engine cylinder which includes the steps of directing unidirectional current through a self-induction coil, interrupting the flow of said current, and discharging the resulting inductive surge of said coil through the primary winding of a transformer, the secondary winding of which is in series with said gap.

10. The method of creating sparks across the gap of a spark plug in an engine cylinder which includes the steps of directing unidirectional current from a source of electrical energy through a self-induction coil, utilizing the magnetic field around said coil to open the circuit between said source and coil, and directing current induced in said coil upon opening of said circuit through the primary winding of a transformer.

11. The method of producing sparks across a gap which includes the steps of directing unidirectional current from a source of electrical energy through a circuit including a self-induction coil, opening and closing said circuit in rapid succession to cause the current through said coil from said source to fluctuate, and directing the current surges thereby induced in said coil through the primary oi. a transformer, the secondary winding of which is in series with said gap.

12. In ignition apparatus, a source of unidirectional electrical current, a pair of separable contacts, means including an induction coil in circuit with said source and contacts for opening and closing the latter to thereby cause the current in said circuit to fluctuate, a transformer having the primary winding thereof connected to the high potential end of said coil, a second induction coil connected in parallel with said primary winding with respect to said source, magnetic means for inducing alternating current in said second induction coil, a circuit breaker connected across said second induction coil, and means for periodically opening said circuit breaker in timed relation with the operation of said magnetic means.

. 13. In ignition apparatus, asource of unidirectional current, a pair of buzzer contacts, means including a self-induction coil connected in cir-' cuit with said source for opening said contacts to thereby interrupt the flow of current through said coil from said source, a transformer having a primary winding, a second induction coil, said winding-and second induction coil being connected in parallel to the high potential end of said first-named induction coil, magnetic means for inducing current in said second induction coil, circuit breaker means connected across said second induction coil, and means for periodically operating said circuit breaker means in timed relation with the operation of said magnetic means. 1

14. In ignition apparatus, a source of unidirectional current, a pairof buzzer contacts, means including a self-induction coil connected in circuit with said source for openingsaid contacts to thereby interrupt the flow of current through said coil from said source, a transformer having a primary winding, a second induction coil, said winding and second induction coil being connected in parallel to the high potential end of said firstnamed induction coil, magnetic means for inducing current in said second induction coil, circuit breaker means connected across said second induction coil, means for periodically operating said circuit breaker means in timed relation with the operation of said magnetic means, a circuit breaker in said connection to the high. potential end of said first-named induction coil, and means for closing said circuit breaker when said circuit breaker means is in open position.

15. In ignition apparatus, a source of unidirectional current, a pair of buzzer contacts, means including a self -induction coil connected in" circuit with said source for opening said contacts to thereby interrupt the flow of current through said coil from said source, a transformer having a primary winding, a second induction coil, said winding and second induction coil being connected in parallel to the high potential end of said firstnamed induction coil, magnetic means for inducing current in said second induction coil, circuit breaker means connected across said second induction coil, means for periodically operating said circuit breaker mean in timed relation with the operation of said magnetic means, a normally open circuit breaker in said connection to the high potential end of said first-named induction coil,

and means for magnetically holding said circuit breaker in closed position when said buzzer contacts are in operation.

16. In ignition apparatus, a source of unidirectional electrical current, a circuit including an inductance and a pair of buzzer contacts connected in series across said source, said buzzer contacts being operable in accordance with the flow of current through said inductance to cause said current to fluctuate, a transformer having a primary winding connected to the high potential end of said inductance, means including a circuit breaker for shunting current around said primary winding, and means for periodically opening said circuit breaker.

17. In ignition apparatus, a transformer having a primary winding and a secondary winding,

a source of unidirectional current, a self-induction coil connected in circuit with said source and through which current from said source normally flows, a circuit breaker in series with said coil and automatically operable to open position whenever the current through said inductance from said source reaches a predetermined value, resilient means for normally closing said circuit breaker, and means for connecting said primary winding to the high potential end of said coil, whereby current induced in said coil upon opening of said circuit breaker is directed through said primary winding.

18. In ignition apparatus, electrical currentgenerating means including a coil and magnetic means for inducing alternating current therein, a

iirst circuit breaker connected across said coil,

means for normally holding said circuit breaker in closed position, means for periodically opening said circuit breaker in timed relation with the operation of said magnetic means, a transformer coil having primary and secondary windings, means for grounding said coils, means connecting the ungrounded side of said circuit breaker to the ungrounded end of said primary winding, 9. condenser connected in parallel with said circuit breaker, a spark gap in series with said secondary winding, whereby a surge of electrical current flows through said primary winding to create a spark at said gap when said circuit breaker is opened, a source of uni-directional electrical current, a second circuit breaker having one side thereof connected to the ungrounded terminal of said source, means for normally holding said second circuit breaker in closed position, an inductance coil having the ungrounded end thereoi connected to the other side of said second circuit breaker, said inductance coil being adapted to electromagnetically open said second circuit breaker when energized by said source, a condenser connected in parallel with said second circuit breaker, a current limiting fuse connected in the circuit between said source and said inductance coil, a resistance having one end thereof connected to the ungrounded end of said inductance. coil, a third circuit breaker having one side thereof connected to the other end of said resistance, means connecting the other side of said third circuit breaker to the ungrounded side of said first circuit breaker, means for periodically closing said third circuit breaker when said first circuit breaker is in open position, and periodically operable circuit breaker means shunting said primary winding for timing the flow of cur- ,means including said inductance for opening said circuit breaker whenever the current through said inductance from said source reaches a predetermined value, whereby current induced in said inductance flows in a surge through said primary winding when said circuit breaker is opened.

. MARC C. SAWYER.