US3259118A - Engine ignition system - Google Patents

Description

July 5, 1966 W Y, PETERS 3,259,118

ENGINE IGNITION SYSTEM Filed March 18, 1963 United States Patent O 3,259,118 ENGINE IGNITION SYSTEM William Y. Peters, Tucson, Ariz., assigner to Jasper N. Cunningham, Los Angeles, Calif. Filed Mar. 18, 1963, Ser. No. 265,744 13 Claims. (Cl. 12S-148) The present invention relates to an improved ignition system .for use with internal combustion engines.

An integral part of all internal combustion engine systems is the ignition system. The ignition system functions in synchronism with the operation of .the engine to develop high voltage signals in a predetermined sequence at the cylinders of the engine. The high voltage signals, in turn, develop -a spark at each cylinder of the engine for igniting the combustible mixture therein, thereby impar-ting a driving force t-o the engine. Thus, it is of prime importance to loptimum engine operation that the ignition system continue to function eiciently over all engine speeds and over long periods of operation.

In conventional ignition systems, such as those commonly employed with present day auto engines, however, 4the spark producing voltage signals decrease in magnitude with increasing engine speed. |Further, high currents are allowed 4to -ow through the mechanical breaker points of the ignition system causing the points to pit, corrode, and wear out rapidly. The corrosion and wearing of ythe points directly affect the eficiency of the ignition system and hence the operation of the associated internal combustion engine.

In an attempt to overcome these problems, improved ignition systems have 'been developed which employ a transistor switching circuit. The transistor switching circuit eectively isolates the breaker points from the spark producing circuitry of the ignition system, reduces the required current tlow through the breaker points, and insures the generati-n of high voltage spark producing signals independent of engine speed.

The improved ignition systems employing transistor switching circuits thereby provide a substantial degree of improvement over the conventional ignition systems. However, in practice, such improved ignition systems are troubled by high kick-back voltages developed across the transistor switching circuit having the generation of the high voltage output signals by the ignition system. The kickback voltages generally exceed the rated back voltage of the transistors comprising `the transistor switching circuit causing them to burn out.

Attempts to overcome the problems cau-sed by kickback voltages in ignition systems employing transistor switches have heretofore included the design of special transistors capable of withstanding the kickback voltages and the use of a se-ries of transistors connected such that a minimum kickback voltage is developed across any one transistor. `Both lof these 'approaches are quite expensive and in practice have proven somewhat unsatisfactory.

The present invention, on the other hand, possesses all of the advantages of the ignition systems employing transistor switching circuits without the accompanying problems of undesired kickback voltages.

More particularly, to accomplish this, the present invention, in a basic form, includes a slightly under-damped series resonant circuit comprising a capacitor and the primary and secondary windings of a saturable core trans- Vformer connected in a series loop. The capacitor is charged and discharged under the control of a normally open switching means to produce a series of high voltage signals in an output means coupled to the series loop circuit. The switching means is connected t-o a direct current source and is `arranged to momentarily close in response to vthe loperation of a timing device, such as a pair Frice of breaker points, to couple to the direct voltage source across the primary winding of the saturable core ltransformer.

Briefly, in operation, the vol-tage coupled to Ithe saturable core transformer produces a current in the secondary winding which ycharges vthe capacitor substantially to the potential -ot the direct current source and sets the direction of magnetization of flux in a first direc-tion within the saturable core 'of the saturable lcore transformer. When Ithe capacitor is substantially charged to the potential of the source, increased current ilow through the primary winding produces a reversal of the direction of magnetization of flux wit-hin the saturable core to a second direction and by transformer action produces an increase in the volta-ge .across the secondary Winding and the capacitor until the core of the transformer becomes saturated. When the core of the transtormer becomes saturated, transformer action ceases and the capaci-tor rapidly discharges through 4the series loop inducing a high voltage output signal at the output means coupled thereto. Due to the saturation of the core in the second direction, current ow from the capacitor in discharging, is in a direction which merely aids the existing direction of magneti- Zation of the saturable core. Thus, a low impedance discharge path is provided for the capacitor to allow the capacitor to rapidly discharge to produce a desired high voltage out-put signal. In addition, due to 'the direction of saturation of the core, little if any magnetic coupling occurs within the saturable core during the discharge of the capacitor. Thus, the capacitor discharges With-out producing an excessive kickback voltage across the switching means. Accordingly, the switching means, which may include a transistor in a non-conducting state, is not adversely eiiected during the discharge of the capacitor.

vIn a second form, the present invention i-ncludes means for sustaining oscillations within the series circuit to produce a controlled oscillatory voltage output in the output Imeans in response to each operation of the timing device. To accomplish this, a feedback circuit is included for periodically closing the switching means to aid in each rei charge of the capacitor.

The above, as well as other features of the present invention, may be more clearly understood Eby reference to .the following detailed description when considered with the drawings, in which:

FIGURE -l is a schematic representation of a basic iform of the present invention;

FIGURES lA-C are schematic representations of modiied Winding arrangements for use in .the form of the present invention illustrated in FIGURE 1; and

FIGURE 2 is a schematic representation of a second form of the present invention.

The ignition system illust-rated in FIGURJE l is arranged Ito produce a high voltage output signal for selective distribution to any one Iof th-e cylinders in `an associated internal combustion engine in response to the operation of a timing means synchronized .to the operation of the engine.

ignition system being arranged to produce a high voltage output signal in response to each opening of the breaker points. The breaker points 10 may be of any conventional design coupled to open and close in synchronism with the operation of the associated engine and are represented, by Way of example only, by the open switch.

As represented, the ignition system of FIGURE 1 includes a slightly under-damped series resonant circuit 12 comprising a capacitor 14, a primary inductive winding 16 of a spark coil transformer 18 and the primary and secondary windings 20 and 21 of a saturable core transformer 22 coupled in a series loop. f i

yBy way of example, the timing means repre-` sented in FIGURE l is a pair of breaker points 10-the t Briefly, a saturable core transformer is a transformer which includes a core of magnetic material having a sub stantially rectangular hysteresis characteristic. The core has a resonant flux that is substantially equal to the saturation luX. Current flow in a rst direction in the primary or secondary winding of the transformer switches the core to a first state of saturation and sets the direction of magnetization of the core in a first direction, while current flow in an opposite direction switches the core to a second state of saturation and sets the direction of magnetization in an opposite or second direction. Once the core is set in one of its saturated states additional current tlow in the sarne direction merely aids the existing direction of magnetization and little if any magnetic coupling occurs within the transformer.

In the winding arrangement illustrated in FIGURE l, the number of turns in the primary winding is substantially less than the number of turns in the secondary winding 21. For example, a ratio of the order of 1:50 has been found suitable. Also, as illustrated, a junction of the primary winding 20 and the capacitor 14 is coupled to a source of reference potential represented as ground While a secondary winding 24 of the transformer 18 is coupled to a junction of the winding 16 and the capacitor 14 and to a distributor arm of a distributor (not shown) for selectively distributing the high voltage pulses developed in the secondary winding 24 to the spark plugs of the associated internal combustion engine. The high voltage signals are developed in the secondary winding 24 in response to the initial discharge of the capacitor 14 after each opening of the breaker points and are followed by a series of signals of substantially reduced and decreasing magnitude caused by the charging and discharging of the capacitor 14 while the breaker points are open.

The selective charging and discharging of the capacitor 14 is controlled by a switch unit 26 which, in turn, is controlled by the opening of the breaker points 10. The switch unit 26, as illustrated, includes, by way of example only, an NPN type transistor 28 and a pair of PNP type transistors 30 and 32. The transistor 28 is arranged in a grounded emitter configuration and includes a base terminal 33 and a collector terminal 34. The base terminal 33 is connected to a junction of a resistor 35 and a capacitor 36, the resistor 35 being coupled to a grounded negative pole of a battery 38 and the capacitor 36 being coupled to the positive pole of the battery 38 through a resistor 40. The collector terminal 34 of the transistor 28 is coupled through a pair of series connected resistors 42 and 44 to the positive pole of the battery 38.

The transistor 30 is arranged in a grounded collector configuration and includes a base terminal 46 coupled to a junction of the resistors 42 and 44 and an emitter terminal 48 coupled through a resistor 50 to the positive pole of the battery 38.

The transistor 32 includes a base terminal 52 coupled through a resistor 54 to the emitter terminal 48 of the transistor 30 and through a resistor 56 to the positive pole of the battery 38. The transistor 32 also includes an emitter terminal 58 coupled to the positive pole of the battery and a collector terminal 60 coupled to a junction point 62 of the primary and secondary windings 20 and 21, respectively, of the saturable core transformer 22.

As illustrated, the distributor breaker points 10 are coupled in series between a junction of the capacitor 36 and the resistor and ground.

The biasing means for the transistors 28, 30 and 32, including the associated resistors and the battery 38, is arranged such that the transistors are normally in a nonconductive state with the breaker points closed. In this state, the capacitor 36 is in a discharged condition.

When the points open, a current flows rapidly through the capacitor 36 to provide a base current for the transistor 28. The transistor 28 immediately switches to a conductive state to draw base current from the transistor 30. The transistor 30 thus switches to a con- 4 ductive state to in turn draw base current from the transistor 32. Thus, in response to an opening of the breaker points 10, the transistors 28, 30 and 32 immediately switch to a conductive state to pass a current signal to the junction point 62 in the resonant circuit 12.

Current ow in the base circuit of the transistor 28 charges the capacitor 36. As the capacitor 36 charges, the base current flowing in the transistor 28 decreases to a magnitude until base current is insuicient to maintain the transistor 28 in a conductive state. The transistor 28 then returns to its normally nonconductive state and in turn causes the transistors 30 and 32 to switch to their nonconductive states.

While the transistor 32 is in a conductive state, current ows from the battery 38 through the emitter-collector circuit of the transistor 32 to the circuit 12. Current passing through the secondary winding 21 charges the capacitor 14 substantially to the supply voltage of the battery 38 and magnetizes the core of the saturable core transformer 22 in a first direction. When the capacitor 14 is substantially charged to the potential of the source 38, current ow through the primary winding 20 produces a reversal of the direction of magnetization within the saturable core to a second direction and by transformer action with the secondary winding 21 produces an increase in the voltage across the capacitor 14 until the core of the transformer becomes saturated. When the core of the transformer becomes saturated, the capacitor 14 rapidly discharges through the primary winding 16 of the transformer 18 to produce a high voltage output signal in the secondary winding 24.

The values of elements comprising the circuit 12 are preferably selected to provide a slightly under-damped discharge path for the capacitor 14. Thus, with the switch unit 26 effectively open, the capacitor 14 discharges substantially to ground potential while the breaker points 1() are open to produce a high voltage output voltage signal in the secondary winding 24. Since the discharge path for the capacitor 14 is slightly underdamped the high voltage output signal is followed by a series of signals of substantially reduced and rapidly decreasing magnitude.

When the breaker points 10 close, the capacitor 36 rapidly discharges to ground and the switch unit 26 assumes its aforementioned initial condition ready for another cycle of operation with the opening of the breaker points.

It is to be noted that during the initial discharge of the capacitor 14 after the opening of the breaker points 10 substantially zero voltage is developed across the transistor 32. This is due to the turns ratio of the transformer 22 as well as the selective setting of the direction of niagnetization of the saturable core prior to the initial discharge of the capacitor 14. In particular, the current flow through the primary winding 20 prior to discharge of the capacitor 14 switches the core of the transformer 22 to one of its saturated states and sets the direction of magnetization of the saturable core in a second direction. Current flow from the capacitor 14, in discharging, is in a direction which merely aids the existing direction of magnetization of the saturable core. Therefore, there is little if any magnetic coupling within the saturable core transformer 22 and only a small voltage drop developed across the primary winding 20 appears across the transistor 32. Consequently, any voltage signal developed across the switching unit during the initial discharge of the capacitor 14 is insufficient in magnitude to have any undesired effects upon the transistors 28, 30 or 32 when in a nonconductive state. Further, due to the damping of the discharge path lthe voltage signals following the initial discharge are of insuflicient magnitude to damage the transistors of the switching unit 26.

It is also to be noted that due to the selective saturation of the core prior to the initial discharge of the capacitor, the `transformer 22 provides a low impedance path for the rapid discharge of the capacitor. The rapid discharge of the capacitor, in turn, pr-oduces a rapid reversal of tiuX within the .transformer 18 to generate an output pulse of increased magnitude.

A modified form of the winding arrangement illustrated in FIGURE l is represented in FIGURE 1A. The winding arrangement 12a of FIGURE lA includes a ternary winding '64 over the windings 2t) and 21 of the saturable core transformer 22. The ternary Winding 64 is coupled to the distributor arm (not shown) and to ground. In lthe winding arrangement of FIGURE lA the opening of the points induces a high voltage output signal in the winding 64. Therefore, the winding arrangement, as represented, does not require the use of the step-up transformer 18 illustrated in FIGURE l.

A second alternative form of the winding arrangement is illustrated in FIGURE 1B. As represented, the circuit 12b includes the secondary winding 21, the capacitor 14, and th-e primary winding 16 of the step-up transformer 18. The primary winding Ztl is removed from the series loop circuit as well as the discharge path for the capacitor 14 and functions independently thereof to provide the aforementioned selective setting of magnetization within the saturable core transformer.

A third alternative form of the winding arrangement for the basic ignition system of the present invention is illustrated in FIGURE 1C. As represented, the capacitor 14 is placed directly across the primary winding 16 of the transformer 1S. In this arrangement the capacitance of the capacitor 14 and the inductance o-f the primary winding 16 are arranged such that when the switching unit 26 closes in response t-o an opening of the breaker points 10 the current signal applied to the resonant circuit 12c rapidly charges the capacitor 14 while producing a minimal voltage signal in the winding 16. The capacitor 14 in such an arrangement discharges through the primary winding 16 to provide an oscillatory output signal of a desired voltage.

In order to insure a more complete combustion of fuel mixture within each cylinder of an associated internal combustion engine it is often desired to produce oscillatory high voltage output signals in a predetermined sequence at each of the cylinders in the internal combustion engine. A preferred form of the present invention for providing such operation is illustrated in FIG- URE 2. The basic arrangement of the circuit illustrated in FIGURE 2 is very similar to that illustrated in FIG- URE 1. Therefore, like reference numerals will be used to indicate like elements and the description of FIGURE 2 will-be limited to the structural and operational distinctions between the embodiments illustrated in FIGURES l and 2.

As represented, the oscillatory ignition system of FIG- URE 2 includes a feedback arrangement for developing a'voltage signal which, when applied to the switching unit 26a, periodically switches .the switching unit between its nonconductive and conductive states while the breaker points 10 are open to produce a series of high voltage signals in the secondary winding 24 of the step-up transformer 1S.

A preferred form of such a feedback arrangement is illustrated as including a ternary winding 66 on the saturable core transformer 22. The ternary winding 66 is coupled between ground and the emitter terminal 68 of the transistor 28. As indicated by the dot notation associated with the primary winding and the ternary winding 66, voltages of like polarity are produced in the primary and the ternary windings. The magnitude of the voltage signal induced in the ternary winding 66 is sufficient, when of a proper polarity, to positively bias the emitter terminal 68 relative to the base terminal 33 of the transistor 28, thereby causing the switching uni-t 26a to switch to a nonconductive state. Similarly, when the switching unit is in a nonconductive state the voltage signal induced in the ternary Winding 66, when of a proper polarity, is sufficient to bias the switching unit to a conductive state.

In ope-ration, then, the switching unit 26a is normally biased to a nonconductive state. When the breaker points 10 are open, the switching unit switches to a conductive state to effectively couple the Vol-tage signal developed by the battery 38 across the primary winding 2t). The voltage coupled to the winding 20 produces a current tiow in the series loop circuit which functions as described in connection with FIGURE l to ultimately charge the capacitor 14 to a voltage above the voltage supplied by the battery 38 and Ito set the direction of magnetization in the saturable core in a second direction. The current flow in the primary winding 20 which causes the desired setting of the direction of magnetization within the saturable core also induces a voltage within the tern-ary winding 66. The voltage induced in the winding 66 is of suicient magnitude and proper polarity to cause the transistor 28 to return to a nonconductive state, thereby switching the unit 26 to a nonconductive state. When this occurs the capacitor 14 rapidly discharges to produce a high voltage output signal in the secondary winding 24 of the step-up transformer 18.

Due to t-he relative direction of magnetization of the saturable core, the discharge current merely aids in the existing direction of magnetization in the saturable core transformer. Therefore, little if any magnetic coupling occurs within the saturable core transformer and a substantially zero voltage is developed across the effectively open switching unit 26a.

Since the discharge path for the capacitor 14 is underdamped, the capacitor 14 discharges and begins to charge in an opposite direction. When the charging is complete, the capacitor then begins to discharge and recharge in its initial direction of charge. As the capacitor begins to discharge, current iiows in .the secondary winding 21 to set the direction of magnetization within the saturable core in its lirst direction and induce voltage signals of like polarity in the primary and ternary windings. The voltage induced in the ternary winding 66 is of sutiicient magnitude and proper polarity to cause the transistor 28 to switch to a conductive state, thereby causing the switching unit 26a to also switch to a conductive state. Thus, while the capacitor 14 is recharging, the switching unit 26a is conductive and is not adversely affected by voltage signals induced in the saturable core transformer 2,2 in switching to its second direction of magnetization.

With the switching unit 26a in a conductive state current ows from the battery 38 to aid in the recharge of the capacitor 14. When the capacitor has charged substantially to the voltage applied by the battery 38, current ow through the primary winding 20 produces a resetting of the direction of magnetization of the saturable core transformer 22 to its second direction and an increase in the voltage across the capacitor 14 by a transformer action. The ow of current'through the primary winding t 2t) also induces a voltage in the ternary winding 66 which causes the transistor 28 to switch to a nonconductive state, thereby causing the switching unit 26a to become nonconductive. The ignition system is then ready to begin again its discharging operation which is repeated at aY relatively high frequency to produce a series of high voltage signals in the secondary winding 24 while the breaker points 10 are open. When the breaker points 10 close, the oscillatory output is retarded. Theentire operation then repeats itself when the breaker points again open.

What is claimed is:

1. A switch controlled capacitor discharge circuit, comprising:

a series resonant circuit including a capacitor and the primary and secondary windings of a saturable core transformer;

output means coupled to the series circuit for developing a voltage signal in response to a changing current flow in the series circuit;

a direct signal source; and switching means for momentarilyl coupling the direct signal source across the primary winding of the saturable core transformer. 2. A switch controlled capacitor discharge circuit, comprising: t

a saturable core. transformer having a primary and a secondary winding vconnected inseries; a series loop circuit including a capacitor and the sccondary winding of the saturablecore transformer; output means coupled to the series loop circuit for deve-loping a voltage signal in response to changing current flow in the series loop circuit; a direct signal source; switching means for coupling the direct signal source across the primary winding of the saturable core transformer; and feedback means responsive to opposite directions of current ow in the primary winding of the saturable core transformer for effectively opening and closing the switching means such that an oscillatory output signal is developedfby the output means.

l3. The apparatus defined in claim 2 wherein the number of turns in the primary winding is substantially less than the number of turns inthe secondary winding.

4. A switch controlled capacitor discharge circuit, comprising: p

a series loop circuit, including a capacitor and the primary and secondary windings of a saturable core transformer; A v output means coupled to the series loop circuit for developing a voltage signal in response to changing current flow in the series loop circuit; a direct signalsource; switching means for coupling the direct signal source across the primary winding of the saturable core transformer; p A and feedback means responsive to opposite directions of current ow inthe primary winding of the saturable core transformerV for effectively opening and closing the switching means such that an oscillatory output signal is developed by the output means. 5. `A switch controlled capacitor discharge circuit, comprising p v n aseries loop circuit including a capacitor and a primary and` a secondary winding of a saturable core transformer; A p output Vmeans coupled to the series loop circuit for developing a voltage signal in response to changing current flow in the seriesv loop circuit; a direct voltage source; n p a signal controlled switch means for coupling the direct voltage source across the primary winding of the saturablelcore transformer; means for biasing the switch meansto a normally open state; means'forswitching said switch means to a closed state in response to an input signal applied thereto; and feedback means rresponsive toa predetermined direction of current iiow in the primary winding of the saturable core` transformer for biasing the switch means to its normally open state such that an oscillatory output voltage signal is developed by the output means. Y 6. In'anengine ignition system having a timing switch means arranged to operate in synchronism with the operation of an associated engine, the combination of a saturated core transformerd having primary and secondary windings connected in series; a series resonant circuit comprising a capacitor and the secondary winding of the saturable core transformer; output means coupled to the series circuit for developing a voltage signal in response to changing current flow in the series circuit; a direct'signal source;

and normally open input switching means coupled to the direct signal source and the series circuit for momentarily closing in response to the operation of the timing switch means to couple the direct signal source across the primary winding of the saturable core transformer. 7. ln an engine ignition system having a timing switch means arranged to operate in synchronism with the operation of an `associated engine, the combination of:

a series loop circuit comprising a capacitor and the- S. In an engine ignition ysystem having -a timing switch means arranged to opera-te in synchronism with the operation of 'an `associated engine, the combination of:

a saturable core transformer having a primary and a secondary winding connected in series;

a series loop circuit comprising capacitor -and the` secondary winding of the saturable core transformer;

output means coupled to the series loop circuit for developing a voltage signal in response to current ow in the series loop circuit;

a direct signal source;

normally open input switching means for closing in response to the operation of the timing switch means.

to couple a direct signal source across the primary winding of the saturable core transformer;

and feedback means responsive to opposite directions of current flow in the primary winding of the saturable core transformer for effectively opening and closing the input switching means such that an oscillatory output signal is developed by the output means.

9. In an engine ignition system having a timing switch means -arranged to operate in synchronism with the operation of an associated engine, the combination of:

a series loop circuit comprising a capacitor and the primary and secondary windings of a saturable core transformer;

output means coupled to the series loop circuit for developing a voltage signal in response :to current iiow in the series loop circuit;

a direct signal source;

normally open input switching means for closing in response to the operation of the timing switch means to couple .a direct signal source across the primary winding of the saturable core transformer;

and feedback means responsive to opposite directions of current tiow in the primary winding of the saturable core transformer for effectively opening and closing the input switching means such that an oscillatory output signal is developed by the output means.

16. In an ignition system h-aving a timing switch means arranged to operate in synchronism with the operation of an associated engine, the combination of:

a capacitor;

a saturable core transformer having a primary and a secondary winding coupled in series with the capacitor to form a series loop circuit;

a direct voltage source;

`a signal control switch means for closing to couple the direct voltage source across the primary winding;

means for biasing the switch means to a normally open state to switch to 'a closed st-ate in response to the operation of the timing switch means;

output means coupled to the series loop circuit for developing a voltage signal in response to changing current ow in the series loop circuit;

and feedback means responsive to \a predetermined direction of current iiow in the primary Winding for biasing the signal control switch means to an open starte.

11. In an engine ignition system having a timing switch means arranged to operate in synchronism with the oper-ation of 1an associated engine, the combination of:

a capacitor;

a saturable core transformer having a primary and a seconda-ry winding coupled in series loop circuit with the capacitor;

la direct voltage source;

normally open input switching means for momentarily closing in response to the operation of the timing switch means to couple the direct voltage source across the primary winding of the saiturable core transformer;

and output means including a ternary winding on the saturable core for developing a volt-age signal in response to changing current flow in the series loop circuit.

12. In an ignition system having a timing switch means Iarranged to oper-ate in synchronism with the operation of an associated engine, the combination of:

a satur'able core transformer having a primary and a secondary winding coupled in series;

a series circuit including .a capacitor, the secondary winding of the satura-ble core transformer, and the primary winding of a spark coil transformer;

a direct current source;

and input switching means coupled to a junction of the primary and secondary windings for momentarily coupling the direct current source across the primary winding of the saturable core transformer in response to the operation of the timing switch means.

13. In an ignition system having a timing 1switch means arranged to oper-ate in synchronism with the operation of an associated engine, the combination of:

a saturable core transformer having a primary and a secondary winding coupled in series;

a spark coil transformer having a primary winding coupled to form a series loop with the primary and secondary windings of the saturable core transformer and having la secondary winding for producing an output signal;

-a capacitor connected across the primary winding of the spark coil transformer;

'a direct current source;

and input switch me-ans coupled to a junction of the primary and secondary windings of the saturable 4core transformer for -momentarily coupling the direct current source .across rthe primary winding of the saturable core transformer in response to the operation of the timing switch means.

LLOYD MCCOLLUM, Primary Examiner.

J. M. THOMSON, W. E. RAY, Assistant Examiners.

Claims (1)

1. 6. IN AN ENGINE IGNITION SYSTEM HAVING A TIMING SWITCH MEANS ARRANGED TO OPERATE IN SYNCHRONISM WITH THE OPERATION OF AN ASSOCIATED ENGINE, THE COMBINATION OF; A SATURATED CORE TRANSFORMED HAVING PRIMARY AND SECONDARY WINDINGS CONNECTED IN SERIES; A SERIES RESONANT CIRCUIT COMPRISING A CAPACITOR AND THE SECONDARY WINDING OF THE SATURABLE CORE TRANSFORMER; OUTPUT MEANS COUPLED TO THE SERIES CIRCUIT FOR DEVELOPING A VOLTAGE SIGNAL IN RESPONSE TO CHANGING CURRENT FLOW IN THE SERIES CIRCUIT; A DIRECT SIGNAL SOURCE; AND NORMALLY OPEN INPUT SWITCHING MEANS COUPLED TO THE DIRECT SIGNAL SOURCE AND THE SERIES CIRCUIT FOR MOMENTARILY CLOSING IN RESPONSE TO THE OPERATION OF THE TIMING SWITCH MEANS TO COUPLE THE DIRECT SIGNAL SOURCE ACROSS THE PRIMARY WINDING OF THE SATURABLE CORE TRANSFORMER.

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