US3516396A - Electronic ignition system - Google Patents

Description

June 23, 1970 H. w. LAWSON, JR 3,516,396

ELECTRONIC IGNITION SYSTEM Filed Oct. 29, 1963 2 Sheets-Sheet 1 FIG. 3 TO ENGINE STARTER SOLENOID INVENTOR. F|G.4 HARRY w. LAWSON,JR.

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ATTORNJ H. w. LAWSON, JR 3,516,396

ELECTRONIC IGNITION SYSTEM June 23, 1970 Sheets-Sheet 2 Filed Oct. 29, 1963 IIO \ I22 I24 I20 I30 l25 I23 P r. (I27 INVENTOR HARRY W. LAWSON, JR.

ATTOR United States Patent 3,516,396 ELECTRONIC IGNITION SYSTEM Harry Wibur Lawson, Jr., 986 Middle Road, Rush, N.Y. 14543 Filed Oct. 29, 1963, Ser. No. 319,883 Int. Cl. F02p 3/06 US. Cl. 123--148 2 Claims ABSTRACT OF THE DISCLOSURE A capacitor discharge type of ignition system is provided with means to charge the capacitor from a source through a power pack and an electronic switch to discharge the capacitor through the coil primary. The switch is triggered by pulses in timed relation with the engine transmitted through an RC circuit determining the on time of the switch.

This invention relates to a novel electrical circuit for use in the ignition system of an internal combustion engine, and constitutes an improvement on the ignition system disclosed and claimed in my prior US. Pat. No. 2,899,632, and on the system described in the article written by me and which appeared in RadioElectronics for July 1962, starting at p. 34, and entitled, Put Electronic Ignition in Your Car.

The ignition system commonly in use today is of the single coil interrupter type. This system is based upon the principle that the interruption of current through a transformer induces a voltage in the primary winding of the transformer proportional to the inductance of the primary coil and the rate of change of current in that coil, and induces a voltage in the secondary winding of the transformer equal to the voltage induced in the first winding multiplied by the turns ratio of the two windings.

This system operates well enough except that it is rough on the contacts that do the interrupting, because the contacts have to carry the entire ignition current. The system is simple and reliable, but fails in many ways to meet the requirements of modern, high-speed engines. During the relatively slow initial voltage buildup, needed coil energy is expended through ground leakage paths in the high voltage wiring. In addition, this slow buildup time, although of no consequence at low speeds, amounts to 2.4 crankshaft degrees at 4000 rpm. In an effort to correct this, automatic distributor advance has been provided, but nonetheless the difference between the optimum and actual firing points increases with speed. Of the most importance, however, is the inability of the present system to function at high engine speeds. The reason for this is the relatively slow rise time of the charging current in the coil, this time being proportional to the ratio of the coil primary inductance to the circuit resistance. Thus, for proper ignition voltage at high speed, the closed point time, or dwell time, in seconds should be in the order of ten times the time constant for the cycle. The condition has been improved by the addition of another set of points Whose function is solely that of increasing the dwell time in order that the charging current may more nearly reach its full value before break but this is expensive.

One object of the present invention is to provide an ignition system which will result in smoother operation of the engine, better high-speed acceleration, and increased life of the points.

Another object of the invention is to provide an ignition system in which a higher voltage may be generated than now is attainable with the conventional breaker and coil system alone.

Another object of the invention is to provide an igni- 3,l6,3% Patented June 23, 1970 tion system with greatly increased firing rate capability, and faster rise in ignition voltage with the result that the ignition system is less affected by high tension leakage losses, and has extremely long breaker point life due to lower voltage and lower current carrying requirements.

One important object of the present invention is to provide a novel electronic ignition system including solid state components, which is capable of providing improved operation of internal combustion engines, especially those subject to relatively wide variations in speed.

Other objects are: to provide a novel electrical circuit of this type, which is capable of providing strong sparking voltages, not only at all normal operating speeds, but also during starting; and to provide a novel electrical circuit of this kind which is highly efiicient, reliable, rugged and long lasting in service, yet which is relatively inexpensive to manufacture and very compact.

The foregoing and other objects and advantages of the invention will become apparent from the following detailed description of representative embodiments, taken in conjunction with the drawings, wherein:

FIG. 1 is a schematic diagram of an electrical circuit built according to one embodiment of the invention and arranged for operation in an ignition system wherein the negative terminal of the direct current power supply is grounded;

FIG. 2 is a schematic diagram of a circuit constructed according to another embodiment of the invention and arranged for operation in an ignition system wherein the positive terminal of the direct current power supply is grounded;

FIG. 3 is a chart showing the voltage output characteristic of the power supply portion of the circuits shown in FIGS. 1 and 2;

FIG. 4 is a fragmentary circuit diagram showing a circuit modification for providing increased sparking voltage output during starting;

FIG. 5 is a fragmentary circuit diagram showing an arrangement for providing repetitive sparking for each firing during engine starting;

FIG. 6 is a fragmentary circuit diagram showing a power input arrangement for use with the circuit when the engine is equipped with an alternator; and

FIGS. 7, 8 and 9 are schematic diagrams showing respectively alternate triggering arrangements for use in place of the conventional distributor breaker points for producing a trigger signal for the circuit of the invention.

Briefly, the invention contemplates the use of a silicon controlled rectifier, commonly called an SCR, or other relatively high current capacity, avalanche type device to control the charging and discharging of a capacitor, which is connected in series with the primary winding of the usual ignition coil, and the provision of an improved circuit arrangement for controlling the operation of the SCR. The energy for firing the spark plugs is derived from the capacitor rather than from the collapse of the magnetic field in the ignition coil, thereby achieving improved eificiency of operation and improved performance at high engine speeds. The use of solid state components including the SCR permits the circuit to be made more rugged and compact than circuits using vacuum tubes, and eliminates the need to make provision for the warm-up period encountered with vacuum tubes.

The invention also contemplates the use of alternate trigger devices in place of the conventional distributor breaker points to provide improved durability, and substantially completely to avoid wear and the risk of point failure.

Referring now to the drawings, the circuit shown in FIG. 1 is arranged for use in connection with an electrical system in which the DC power supply, such as the battery 10, has its negative terminal grounded. The circuit is connected to the positive terminal of the battery through a conventional ignition switch 12, one contact of which is connected through a conventional limiting resistor 14 to the common terminal 16 of a conventional ignition coil 18. Resistor 14 may be the non-linear ballast resistor or resistance wire normally found in present day vehicles between the ignition switch and the ignition coil. The resistor 14 may be removed, if desired, and the connection between-the ignition switch 12 and the common terminal 16 of the coil broken, but preferably, the common terminal 16 is merely grounded by a removable jumper 20 so that the system may be more easily returned to conventional operation in the event of failure of one of the components or circuit malfunction.

The circuit is energized by the battery 10 through a conventional transistor inverter power supply 22 and a rectifier 24. This power supply provides, for instance, a nominal one hundred to one hundred and twenty-five volts DC at point 25 relative to ground.

The main capacitor 26 of the system is connected between the primary winding 28 of the ignition coil and the output terminal of the rectifier 24 in series with a diode 30 and a charging inductor 32. The capacitor 26 is also connected between the primary winding 28 of the ignition coil and ground through the silicon controlled rectifier or SCR 34.

During the intervals between sparks, the capacitor 26 charges to about twice the value of the output voltage of the power supply rectifier 24 due to the effect of the inductance of the inductor 32 and the ignition coil 18. A spark is produced when the SCR 34 is triggered permitting the capacitor 26 to discharge rapidly through the primary winding 28 of the ignition coil. During discharge, the inductance of the ignition coil causes current to continue flowing after the capacitor is fully discharged, and brings about a charge reversal on the capacitor 26. The capacitor 26 discharges completely and then becomes charged in the opposite polarity, thereby producing a reverse bias on the SCR 34 and positively cutting it off. The capacitor 26 is then recharged through the charging inductor 32.

During the initial portion of the recharging period until the polarity of the capacitor 26 again reverses, part of the charging current is supplied through a diode 36 and a resistor 38, which are connected in series with each other across the SCR 34. This current produces a voltage across the resistor 38, the time integral of which is directly proportional to the rate of sparking and therefore to the engine speed. A voltmeter 40 connected across the resistor 38 serves to integrate the voltage and to provide an indication of the integrated value thereof. The voltmeter 40 may be calibrated directly in r.p.m.s to serve as a tachometer.

As shown, the triggering of the SCR 34 is controlled by the regular breaker points 42 through an RC circuit to insure against premature firing due to contact bounce of the breaker points 42, which often occurs upon closing of the contact points. It is desired to fire only when the breaker points 42 are driven open by the distributor cam 44, and to avoid firing when they bounce open. The RC circuit includes a capacitor 46, one plate of which is connected to the insulated breaker point 48 and, through a resistor 50 to the ignition switch 12. The other plate of the capacitor 46 is connected to the trigger electrode 52 of the silicon controlled rectifier through a resistor 54. A diode 56 is connected in parallel with the resistor 54 and oriented to block current from flowing toward the capacitor 46. Another resistor 58 is connected between the trigger electrode 52 of the silicone controlled rectifier and ground. Resistor 58 is merely a swamping resistor of low enough value to normalize the range of current coming from the firing circuit.

In the intervals between sparks, the points 42 are closed, grounding the right-hand plate of the capacitor 46. The battery voltage therefore appears across the resistor 50, and the capacitor remains discharged with both of its plates at ground potential. When the breaker points open, the entire battery potential appears initially across the charging resistor 50 in series with the trigger electrode 52 of the SCR. The series resistor 54 is effectively shorted during the period by the diode 56. The SCR is fired by flow of the current into the gate lead or trigger electrode 52 and out the cathode lead 53. The amount of current in this path to fire the SCR is a function of the particular SCR used and the temperature of the SCR.

The value of the charging resistor 50 is relatively small so that fully adequate current flows to trigger the SCR. During the time the points 42 remain open, the battery voltage is transferred exponetially back to the trigger capacitor 46, which is thus charged with its lefthand plate negative and its right-hand plate positive. Due to the relatively low value of the resistance in this circuit, the charging of the capacitor 46 is relatively rapid, and is sufficiently fast to assure that the voltage on the trigger electrode 52 drops to a value below the trigger voltage of the SCR before the main capacitor 26 becomes re-charged.

When the points 42 thereafter close, the trigger capacitor 46 discharges and returns to ground potential again. Its discharge path, however, is now through resistor 54 rather than through diode 56. Hence the discharge time is longer than the charge time. This prevents re-sparking in response to contact bounce. The contacts 42, 48 constitute a mechanical switch and although they open precisely their closing is subject to imperfection in the form of contact bounce. Contact bounce in the interval immediately after closing is in effect a false firing signal for the SCR and its effect is eliminated by the combination of resistor 54 and diode 56 which provide a fast-attack, sl0w-release trigger signal by causing fast capacitor charge and slow discharge. In the embodiment of FIG. 1, the capacitor 46 discharges also through resistors 50 and 58. The resistor 54 is brought into play during discharge of the capacitor 46 by reason of the orientation of the diode 56, which does not permit current to flow through it in a discharging direction but only in the charging direction. Similarly, the resistor 58 is brought into play because of the current blocking effect of the trigger electrode 52 of the silicone controlled rectifier. The negative voltage on the left-hand plate of the trigger capacitor 46 is thereby maintained and a sufficient portion of it appears on the trigger electrode 52 of the silicone controlled rectifier for a sufficient time to insure against inadvertent firing such as might otherwise be caused by contact bounce of the breaker points 42.

The circuit shown in FIG. 2 is essentially the same as the one shown in FIG. 1 except that the vehicular battery is reversed, and the positive terminal of the battery is grounded. This causes the firing circuit trigger current flowing through capacitor 46 to reverse. To accommodate this, the rectifier diode 66 is added between the SCR cathode 53 and ground, and the negative trigger pulse is applied at the SCR cathode. Thus a negative current pulse applied at the SCR cathode accomplishes the same result as a positive current pulse at the gate 52'. Resistor 38 in series with reverse diode 36 provides increased voltage drop to assist turn-off of the SCR in the reverse direction as well as providing an ideal take-off point for the connection of the tachometer comprising the multiplier resistor 68 and DC milliammeter 40. Unidirectional negative voltage pulses occur across resistor 38; and these are integrated in the simple metering systern shown. The average DC current drawn from the power supply is also a direct reading of the firing rate or engine r.p.m. In the circuit shown in FIG. 2, the trigger capacitor 46 is connected between the insulated contact 48 of the breaker points and the cathode 53 of the SCR through the discharging resistor 54 in parallel with the diode 56'. The trigger electrode 52 of the SCR is grounded.

The diode 56' operates similarly to the diode 56, but with reversal of polarity, to prolong the discharging time of the trigger capacitor 46 thereby to insure against undesired firing due to contact bounce or other factors.

It should be noted that no modification of points 42, 48 is necessary due to a positive grounded battery, which is normally the case for the conventional transistor ignition system where both sets of points must be insulated.

During starting, the drain of the cranking motor on the battery usually causes a reduction in the voltage output of the battery with a consequent reduction in the sparking voltage. Any ignition system must be capable of supplying full ignition voltage to the spark plugs even at half battery voltage which may occur when cranking an engine in cold weather. This can be accomplished either: (1) by providing double normal operating voltage, or (2) by boosting operating voltage during cranking. The first is uneconomical. The circuit of the invention using unregulated power supply comprising the inverter 22 and the rectifier 24 automatically provides a high degree of compensation for the reduction in battery voltage during starting. The curve 55 in FIG. 3 shows the voltage output of the unregulated power supply as a function of load variation, the voltage input being held constant.

During starting, the sparking rate is relatively low, there is very little drain on the inverter- rectifier power supply 22, 24, and its voltage output is relatively high, nearly twice the value it would be with the same input voltage but under heavier load conditions. When, therefore, the battery voltage is reduced to about half its normal value due to the current drain of the starting motor, the output of the inverter/ rectifier 22, 24 will still be at about the same value as when the battery voltage is normal and the engine is running at idling speed or faster. After starting, the battery voltage increases, and the output characteristic of the inverter rectifier supply decreases, thereby tending to maintain the sparking voltage at its normal value at all times.

It is also of advantage, particularly when starting in cold weather, to provide sparking voltages above the normal operating value, thereby to improve the ignition of relatively cold fuel mixtures. One circuit arrangement for achieving this is shown in FIG. 4. According to this arrangement, the secondary winding 62 of the transformer 64, which couples the output of the inverter 22 to the rectifier 24, is grounded through the operating contacts of a single pole-double throw relay 60. The relay 60 is connected through the electrical circuit of the engine to be energized simultaneously with the starter solenoid (not shown) and to be deenergized at all times when the starter solenoid is deenergized.

Normally, the center tap 65 of the winding 62 is grounded through the relay contacts 61, and the rectifier 24 operates as a full wave rectifier. Normal power supply output is therefore derived from a conventional full-wave center-tap rectifier configuration using rectifier diodes 69 and 71. When the relay 60 is energized, however, during cranking contact, the relay arm 61 is picked up, and disconnects the center tap 65 from ground and grounds one end terminal of the winding 62 so that the rectifier 24 operates as a half wave rectifier using rectifier diode 69 only, but with the full winding voltage of the power supply transformer. One half battery voltage during cranking therefore still results in normal operating ignition voltage.

The circuit modification shown in FIG. 5 operates as a further starting aid to reduce charge leakage from the capacitor 26 during starting and to provide a series of sparks in rapid succession during each interval for which the breaker points are open, thereby not only to avoid the effects of spark deterioration due to charge leakage from the main firing capacitor 26, but also to provide heavier sparking during starting. When the ignition switch is first turned on, capacitor 26 reaches a maximum of full power supply voltage. As described in my prior Pat. No. 2,899,632, charging of the capacitor 26 to nearly twice the power supply voltage occurs only under conditions of repetitive firing operation. Capacitor 26 tends to discharge from this higher peak value when this repetition rate is very low.

According to the modification shown in FIG. 5, a uni junction transistor pulse oscillator, comprising the unijunction transistor 74, capacitor 82, and resistor provides repetitive firing when points 42, 48 are open to supply interbase voltage via line 83 during cranking only. Such an oscillator is known per se, but is unique in the present system in that it provides coincidence requirements of open points and cranking voltage in order to provide continuous plug firing. The transistor is connected in the trigger portion of the circuit for triggering the SCR. One base lead 72 of the uni-junction transistor 74 is connected to the insulated breaker point 48. The second base lead 76 is connected to the trigegr electrode 52 of the SCR 34. The emitter 78 is connected through a resistor 80 for energization simultaneously with the engine starting solenoid, and, through a timing capacitor 82, to ground. During the normal operation of the engine, the emitter 78 is deenergized, and the uni-junction circuit is inoperative and has substantially no effect. During starting, voltage is applied to the emitter 78, and the circuit oscillates whenever the breaker points 42 are open. During the intervals when the points 42 are closed, the first base lead 72 is grounded and the uni-junction trausistor 74 is non-conductive and has substantially no effect on the circuit. During starting, therefore, the circuit 7t) oscillates repetitively during each firing period to trigger the SCR 34 at a relatively high rate during times when the breaker points are open, thus providing improved ignition for starting under adverse conditions.

Certain vehicles are now equipped with alternators in place of direct current generators. In such cases, as shown in FIG. 6, the inverter portion 22 of the circuit may be omitted, and power taken from a single phase output of the alternator 90, through the transformer 64 and the rectifier 24.

The alternator voltage is normally a relatively low AC voltage varying in frequency from about 45 c.p.s. to 1200 c.p.s. This is transformed to the proper level DC voltage at point 25 by means of transformer 64, rectifier diodes 69 and 71, and filter capacitor 35. Since this voltage does not become available until after the engine is started, it is necessary to provide an alternate source of direct current for engine starting. For this purpose a small mercury type battery 92, preferably of the rechargeable type, may be used since drain under starting conditions is less than 1 ma., and the battery will have a life approaching shelf life. The battery 92 is connected between the high voltage output of the rectifier 24 and ground, in series with a current limiting resistor 94, which is shunted by a diode 96. The diode 96 is oriented to provide a current path for starting when the starting switch 98 is closed. It permits current flow from the battery 92 into the operating circuit, and blocks current flow from the rectifier 24 into the battery 92. The limiting resistor 94 provides a charging path for trickle charging of the battery 92, after the engine is started, and power supply slightly exceeds the voltage of battery 92. A switch 98 is preferably included in series with the battery 92, and arranged to be controlled by the ignition key so that it is opened during times when the vehicles engine is turned off.

Because of mechanical wear on breaker points, arcing, and problems with contact bounce, and the like, it is proposed to substitute a trigger arrangement without physical contact. My system is especially well suited for use with such trigger arangements, three of which are shown in FIGS. 7, 8, and 9, respectively.

In FIG. 7, there is shown an optical arrangement using a photoelectric cell or photo-sensitive switch 104. A disc 100 replaces the breaker points 42 and cam 48 in this arrangement. The switch 104 blocks current flow in darkness and becomes a current path when illuminated. The disc 100 has a plurality of radially arranged slots 101, one such slot for each of the cylinders of the engine. The disc 100 is mounted on the rotor of the distributor for rotation at one half of the engine speed for a four cycle engine, or synchronously with the engine for a two cycle engine. A lamp 102 is mounted on one side of the disc 100, and the photocell 104 is mounted on the opposite side of the disc. The output of the photocell 104 controls the operation of a uni-junction transistor 106, which is connected to the trigger electrode 52 of the SCR 34 for firing it.

During intervals between sparks, the photocell 104 is shielded from the lamp 102 by the solid portion of the disc 100. When the disc rotates sufficiently to bring one of the slots 101 into register with the optical path between the lamp 102 and the photocell 104, the photocell 104 conducts, triggering a conventional uni-junction transistor 106, which in turn triggers the SCR 34 to produce a spark. The circuit, aside from the photocell 104, comprises transistor 106, register 107, capacitor 109, and oscillator base load or SCR gate swamping resistor 112. With the light sensitive cell 104 dark, capacitor 109 charges to full battery voltage via resistor 112. When a slot 101 registers with the cell, capacitor 109 discharges via cell 104 and the unijunction transistor to provide a positive, SCR firing pulse across resistor 112. Should light remain on the cell 104, firing is repetitive due to the relaxation oscillator characteristics of the circuit.

The firing rate is determined basically by the RC product of resistor 107 and capacitor 109. The width of the slots 101 and the value of the RC product is such that for all speeds above idle, discharge of capacitor 109 occurs only once per slot. Below idle or cranking speed, repetitive firing is automatically achieved, resulting in good starting characteristics.

The voltage dropping resistor 108 in series with the lamp 102, and the diodes 110 and 111 in parallel with the lamp 102 are provided as shown for regulating the voltage applied to the lamp 102 in order to insure maximum life for the lamp. The lamp used may be of the miniature, prefocused, spot type with a nominal operating voltage of 2.5 volts. Such a lamp at that voltage has a life in the neighborhood of 50,000 hours, and much higher at lower operating voltage. By the use of forward based silicon diodes 110, 111, the lamp voltage is regulated at a value of about 1.4 volts.

The arrangement shown in FIG. 8 is essentially the same as the arrangement shown in FIG. 7, except that a source 116 of high energy radiation such as gamma radiation is used in place of the lamp 102, and a radiation detector 118 is used in place of the photocell 104, thus avoiding the requirement of providing elecrical connections for the lamp 102. The gamma ray source 116 may be a self-energizing, long lasting radioactive material such as, for example, a tiny bit of cobalt 60. The device 118 is, of course, sensitive to radiation and provides a conducting path when illuminated by nuclear radiation. The disc 100 should be made of a radiation impervious material.

A magnetic system is shown in FIG. 9, but this system is much different from the conventional magnetic pickup system which is speed or velocity sensitive. The pickup type system is useless at zero or near zero cranking speeds. The circuit of FIG. 9 includes a conventional blocking oscillator 120 made up of a silicon transistor 121, resistors 123, 125 and capacitor 127, together with the feedback coupling transformer containing collector winding 129 and base winding 1.31. The core 124 coupling the two windings is an incomplete loop, closed periodically by the rotation of the pole piece 128 coupled 8 to the distributor shaft. Line 133 connects with the ignition switch.

The output of oscillator is connected to the trigger electrode 52 of the SCR. The feedback loop of the oscillator is magnetically coupled through transformer 122, the core 124 of which provides a relatively long magnetic gap 126. The star-shaped, magnetic pole piece or rotor 128 rotates with the rotor of the distributor; and when the points .130 of the rotor come into alignment with the pole faces (not separately designated) of the core 124 of the transformer, the reluctance of the core 124 is sufficiently reduced to permit the oscillator 120 to start its cycle, thereby firing the SCR 134. At all other times, that is, when the points 130 of the rotor are away from the pole faces of the core 124, the reluctance of the core 124 is relatively high, sufiiciently so that there is not enough coupling in the feedback loop to permit oscillation, and the oscillator is effectively cut ofi. Only a small leakage current flows through the transistor 132, enough to ensure the start of the next oscillation, but not enough to trigger the SOR 34.

Again, should the pole piece remain aligned in the core 124, repetitive firing results at a rate determined by the RC product of resistor and capacitor 127. Positive firing pulses from the transistor emitter appear across resistor 123 and are applied to the gate 52 of the SCR. Core and pole piece dimensions as Well as RC products are adjusted so that, at all speeds from idle up, only one firing pulse per cylinder results. By this means the drawback of magnetically induced pickup triggering voltage is eliminated.

-It is to be noted that the entire circuitry of the three systems shown in FIGS. 7, 8 and 9 can be installed within the compass of conventional, present-day engine distributor housings. They are also adaptable for retrofit installations on existing engines. This magnetic system is believed to be highly advantageous and superior to other magnetic pick-up systems for use with ignition systems of automobiles and the like in that it is not velocitysensitive, and is, therefore, equally effective during slow cranking of the engine and under normal conditions when the engine is operating at idling and higher speeds.

While the invention has been described in connection with several different embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention or the limits of the appended claims.

Having thus described my invention, what I claim is:

1. An electronic ignition circuit for an internal combustion engine comprising:

(a) a triggerable avalanche device,

(b) a capacitor,

(c) means for connecting said avalanche device and said capacitor in series with each other and with the primary winding of the ignition coil of the internal combusion engine,

(d) means for charging said capacitor to a voltage less than the breakdown voltage of said avalanche device during period when said avalanche device is in its OFF condition, and

(e) an RC circuit portion for triggering said avalanche device responsively to a signal produced by the engine, said circuit portion including:

(1) a trigger capacitor,

(2) a resistor connected in series between said trigger capacitor and said avalanche device, (3) a diode in shunt across said resistor and oriented in a direction to by-pass said resistor 9 10 when said avalanche device is ON and to re means for enabling said oscillator during ignition perisist current flow when said avalanche device ods while the engine is being cranked by its starter is OFF, and motor, (4) means responsive to the engine timing syssaid oscillator of said second trigger circuit including tem for periodically alternately applying a voltan inductively coupled feed back loop including a age across said RC circuit portion and said 5 transformer having a magnetic core, said core havavalanche device and removing the voltage ing an air gap of sufiicient length effectively to detherefrom thereby periodically to fire said avacouple said loop and thereby disable said oscillator, lanche device. said means for disabling and said means for enabling 2. An electronic ignition circuit for an internal comincluding a magnetic rotor rotatable in said air gap, bustion engine comprising said rotor having projecting portions which are a triggerable avalanche device, alignable across said gap, and means for rotating a capacitor, said rotor in timed relationship to the rotation of the means connecting said avalanche device and said carotor of the distributor of the engine, whereby when pacitor in series with each other and with the prisaid projecting portions come into alignment across mary Winding of the ignition coil of the engine, said gap, the first-named rotor completes the coumeans for charging said capacitor to a voltage less pling in said feedback loop and thereby enables said than the breakdown voltage of said avalanche device oscillator. during period when said avalanceh device is in its References Cited OFF UNITED STATES PATENTS a first trigger clrcult for triggering said avalanche device in timed response to rotation of the distributor 2,791,724 5/1957 Ekblom et rotor of the engine during normal operation, 2,898,392 8/1959 Jaeschkea second trigger circuit for triggering said avalanche 2980322 4/1961 Shot? device at a rate independent of the rate of rotation 2,984,695 5/1961 Befrdme et of the distributor rotor, said second trigger circuit 3,051,870 8/1962 including, 3,131,327 4/1964 Quinn. an oscillator for producing repetitive trigger signals at a rate dependent upon its circuit parameters, LAURENCE GOODRIDGE Pnmary Exammer means for disabling said oscillator during normal engine operation and during the intervals between ignition periods, and 315209 US. Cl. X.R.

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