Controlled Variable Spark Capacitor Discharge Ignition System

Abstract

A capacitor discharge type ignition system is arranged to deliver pulses of energy to the distributor of an engine, thereby to generate ignition sparks. A control circuit is provided for controlling the duration of the energy pulses, and hence the duration of ignition sparks, as a function of selected operating conditions of the ignition system and its associated engine, such as, supply voltage level, operating temperature and engine speed.

Description

The present invention relates to ignition systems and more particularly to an improved ignition system of the capacitor discharge type suitable for use with engines, such as internal combustion engines, rotating turbine engines and the like, having a source of direct current for energizing same.

Heretofore, engine ignition systems have been developed of the capacitor discharge type and one common use of such ignition systems has been in the automobile. Generally, the operation of these systems is controlled by breaker contacts which are opened and closed in synchronism with the movements of the pistons of an associated engine. Thereby, the discharge of a storage capacitor through the primary of an ignition coil is timed so that ignition sparks are delivered in a timed sequence to ignite combustible fuel which provides the energy to drive the engine. Typically, such ignition circuits have only been capable of generating sparks of substantially uniform durations and an example of such an ignition circuit is shown in U. S. Pat. application, Ser. No. 456,789 filed May 18, 1965, now Pat. No. 3,604,978 which is assigned to the assignee of the present invention.

It has been discovered that a significant disadvantage exists with such prior art ignition systems since they are only capable of generating sparks of uniform duration. This disadvantage is due to the fact that it has been found desirable to control ignition spark duration as a function of the conditions under which the ignition system and its associated engine are operated, thereby to prevent premature ignition and energy waste, reduce wear on the component parts of an ignition system, and improve overall engine efficiency. For example, it has been found desirable to increase spark duration whenever the voltage level of the D.C. source supplying the ignition circuit is low to insure complete combustion of the fuel mixture delivered to drive the engine. Likewise, it has been found desirable to increase spark duration whenever the engine is operated at low temperatures to insure complete fuel combustion. On the other hand, it has not been found necessary, nor desirable, to provide long duration sparks whenever the engine is operating at high speeds or rotation rates since spark energy is thus wasted, the components of the ignition system are unduly stressed and premature ignitions of fuel in the engine cylinders next in the firing sequence are likely to occur.

Another disadvantage frequently found with such prior art ignition systems is that they may be inadvertently triggered to discharge the storage capacitor by bounce of the breaker contacts upon closure. Such inadvertent opening of the breaker contact points, so called contact bounce, is a problem particularly associated with high speed point operation such as occurs during the high speed operation of an automobile engine.

It is accordingly, an object of the present invention to provide an improved engine ignition system which is operable to control ignition spark duration.

It is, further, an object of the present invention to provide an improved engine ignition system which controls ignition spark duration as a function of selected conditions under which the ignition system and its associated engine are operated.

It is, additionally, an object of the present invention to provide an improved engine ignition system of the capacitor discharge which controls ignition spark duration as a function of the voltage level of its associated D.C. source, the speed of its associated engine and operating temperature.

It is also an object of the present invention to provide an improved engine ignition system of the capacitor discharge type which is substantially insensitive to contact bounce thereby to eliminate the inadvertent generation of ignition sparks and prevent misfiring.

In accomplishing these and other objects, there is provided in accordance with the present invention a capacitor discharge ignition system associated with an engine in which a storage capacitor is charged to a relatively high potential by means of a low potential D.C. source and a D.C.-- D.C. convertor. Switch means preferably in the form of a silicon controlled rectifier are selectively operated by means of a control circuit to connect the charged storage capacitor across the primary of an ignition coil. Thereby, energy stored in the storage capacitor is delivered to the ignition coil by the ringing action of the L-C circuit formed by the storage capacitor and the ignition coil, and ignition sparks are generated at the spark gaps of a distributor connected across the secondary of the ignition coil. The control circuit which operates the SCR switch means controls the duration of the closure of the switch means as a function of the voltage level of the D.C. source, operating temperature and engine speed, thereby to control ignition spark duration as a function of these variable operating conditions. Breaker contacts or other suitable means are included to operate the control circuit so as to time the closure of the switch means so that the ignition sparks are generated in synchronism with the movement of the engine's cylinders and the control circuit is designed so as to be not responsive to momentary openings of the breaker contact points as caused by contact bounce. Thus, an improved engine ignition system which is operable to control ignition spark duration as a function of selected variable conditions is provided.

A better understanding of the present invention may be had from the following detailed description when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an ignition system according to the present invention;

FIG. 2 is a graphical representation of a typical voltage wave form generated across the ignition coil primary of the ignition system of FIG. 1 when the system is operated under supply voltage, temperature and rate conditions considered normal or standard;

FIG. 3 is a graphical representation of a typical voltage wave form generated across the ignition coil primary of the ignition system of FIG. 1 when the system is operated at a relatively low level of supply voltage with temperature and rate conditions normal;

FIG. 4 is a graphical representation of a typical voltage wave form generated across the ignition coil primary of the ignition system of FIG. 1 when the system is operated at a relatively high rate operation will supply voltage and temperature conditions normal;

FIG. 5 is a graphical representation of a typical voltage wave form generated across the ignition coil primary of the ignition system of FIG. 1 when the system is operated at a relatively low temperature with supply voltage and rate conditions normal.

Referring to the drawings in more detail, there is shown in FIG. 1 an engine ignition system including a D.C. voltage source in the form of a battery 10. The battery 10 is a low potential D.C. source which preferably supplies approximately 12 volts D.C. Connected in series with the battery 10 to its positive pole is an ignition switch 11 for switching the ignition system on and off. A D.C.--D.C. convertor 13 has its input leads 14 connected across the series-connected battery 10 and switch 11 for receiving the voltage from the D.C. source 10. The circuitry of the convertor 13 is shown enclosed in broken lines and includes a pair of transistors 15 parallel connected across the primary of a voltage step up transformer 16 to receive from the leads 14 the D.C. voltage supplied by the battery 10. Connected across the secondary of the transformer 16 are the input terminals of a diode bridge 17. The bridge 17 rectifies the alternating voltage applied to its input terminals by the transformer 16 to generate a high potential D.C. voltage across electrical leads 18 and 19 which are connected to the output terminals of the bridge 17. The leads 18 and 19 are connected, respectively, to the positive and negative terminals of the bridge 17. The D.C.--D.C. convertor 13 functions to convert the 12 volts D.C. received from the battery 10 into a high potential D.C. voltage of approximately 400 volts. It is noted that the construction of the convertor 13 is conventional and that a detailed discussion of its operation may be found in the article, "A New Ignition System for Cars," by R. Van Houten and John C. Schweitzer in the Oct. 5, 1964, edition of the magazine ELECTRONICS.

Connected to the lead 18 is one terminal of a storage capacitor 25. Connected between the other terminal of the capacitor 25 and the lead 19 is the primary winding of an ignition coil or output transformer 26. A shunting capacitor 27 is connected in parallel with the primary of the ignition coil 26 to shunt and thereby substantially eliminate the effects of any electromagnetic interference on the output generated by the ignition coil 26. Connected across the secondary winding of the ignition coil 26 is a standard distributor and spark plugs represented by a single spark gap 28. The distributor and spark plugs represented by the gap 28 are conventional in operation and may be operated by a mechanical drive arrangement coupled to the drive shaft of a conventional engine (not shown) which is associated with the exemplary ignition system. Thereby, potentials developed by the ignition coil 26 are delivered or distributed in a timed sequence in a well known and conventional manner to the spark gaps 28 of the spark plugs associated with the cylinders or combustion chambers of the conventional engine and ignition sparks are generated which ignite combustible fuel delivered to the engine cylinders to drive the engine. It is noted that the engine driven by the exemplary ignition circuit may be of any type which is driven by spark ignition, such as, internal combustion engines, rotating turbine engines and the like.

Connected between the leads 18 and 19 is a choke coil 29 connected in series with the anode-cathode path of conduction of a SCR 30. The coil 29 has one terminal connected to the lead 18 and its other terminal connected to the anode electrode of the SCR 30. The cathode electrode of SCR 30 is connected to the lead 19. A diode 31 is connected in parallel with the coil 29 with the cathode electrode of the diode 31 connected to the lead 18 and its anode electrode connected to the point of common connection of the coil 29 and SCR 30. The SCR 30 functions as a selectively operable switch means which when closed connects the storage capacitor 25 across the primary of the ignition coil 26. Thereby, as is hereafter explained, the energy stored in the capacitor 25 is delivered to the ignition coil 26 so that an ignition spark is generated at the spark gap 28. The parallel-connected diode 31 and choke 29 function to control current through the SCR 30 when it is conducting, i.e., when the switch means is closed, thereby to control the current rise through the SCR to increase the reliability of the ignition circuit.

In order to control the operation of the switch means provided by the SCR 30, a control circuit 40 is provided which is connected to the gate electrode of the SCR 30 for closing the switch means provided by the SCR 30 by gating it into conduction. The control circuit 40 includes resistors 41, 42 and 43 which are each commonly connected at one of their terminals. The other terminals of the resistors 41, 42 and 43 are connected, respectively, to the switch 11, the collector electrode of an NPN transistor 44 and one terminal of a resistor 45. The other terminal of the resistor 45 is connected to the base electrode of the transsistor 44. The emitter electrode of the transistor 44 is connected to the lead 19 and the lead 19 provides a bus of reference potential since it is connected as a return lead from the negative output of the bridge 17 to the negative pole of the battery 10. Connected between the lead 19 and the base electrode of the transistor 44 is a resistor 46, and a capacitor 47 is connected from the common point of connection of resistors 43, 45 to the lead 19.

To initiate the operation of the control circuit 40 breaker points or contacts 48 are included therein connected between the common point of connection of the resistors 41-43 and the lead 19. The breaker points 48 are conventional in construction and are operated by a mechanical arrangement or gearing (not shown) which is coupled to the drive shaft of the engine associated with the ignition system. Thereby, a series of time signals or conditions is produced which is in synchronism with the movement of the pistons in the associated engine. Although the exemplary circuit is illustrated as using breaker points as the timing means for synchronizing the operation of the control circuit 40 with engine movement, it is apparent that other means and methods may be used with equal success, such as devices which utilize magnetic, photoelectrical or Hall effect characteristics to sense the appropriate moments for firing and developing a control signal suitable for controlling the ignition system of the present invention. Connected across the breaker points 48 for developing a voltage when the points 48 are open is a points capacitor 49.

The control circuit 40, as is hereinafter explained, functions to generate a switch control signal the duration of which is a function of the voltage level of the battery 10, the rate the points 48 are opened and closed, and the operating temperature of the circuitry and engine. To sense operating temperature, the transistor 44 is selected to be temperature sensitive so that its forward bias point or voltage is inversely proportional to temperature, e.g., as the temperature decreases the forward bias voltage increases. The control signal of the control circuit 40 is generated as an output across a load resistor 50 which is connected between the collector electrode of the transistor 44 and the return lead 19. The terminal of the resistor 50 in common with the collector electrode of the transistor 44 is connected to the gate electrode of the SCR 30 so that the switch control signal developed on the load resistor 50 is applied thereto. A capacitor 51 is connected in parallel with the resistor 50 for shunting electromagnetic interference so as to eliminate such interference from the control signal applied to the gate of the SCR 30.

During operation of the exemplary ignition system, the ignition switch 11 is closed so that low potential D.C. voltage is supplied from the battery 10 to the convertor 13 and the control circuit 40. The D.C.--D.C. convertor 13 operates to charge the storage capacitor 25 to a high potential D.C. voltage. With the supply voltage provided by the battery 10 at its normal or standard level 12 volts, the convertor operates to charge the storage capacitor 25 to approximately 400 volts D.C. when the switch means provided by the SCR 30 is closed.

With the storage capacitor 25 charged, the breaker points 48 are opened in synchronism with engine movement. Upon the opening of the points 48, the current flow through the resistor 41 which had been flowing through the closed contacts 48 rapidly charges the points capacitor 49 and the charged capacitor 49 establishes a current flow through the resistors 42 and 43. The current through the resistor 42 also flows through the load resistor 50, thereby a control voltage sufficient to bias the SCR 30 into conduction is applied to the SCR gate electrode.

With the SCR 30 conducting, the series-connected SCR 30 and choke 29 places substantially a short circuit across the leads 18 and 19. Thereby, the energy represented by the D.C. voltage across the output terminals of the bridge 17 is dissipated and absorbed by the transformer 16 and a short is reflected into the primary of the transformer 16. The reflected short removes the driving signal from the inverter oscillator formed by the transistors 15 and transformer 16 so as to stop the operation of the convertor 13. The conduction of the SCR 30 also causes a closed L-C circuit to be formed made up of the charged storage capacitor 25, the primary of the ignition coil 26, the SCR 30, and the parallel-connected diode 31 and choke 29. The storage capacitor 25 thus discharges through the primary of the coil 26 so that an ignition spark is generated by the energy delivered to the coil 26 across the spark gap 28, and the choke 29 and diode 31 function to control SCR current and the voltage rise across the ignition coil primary.

It is noted that with SCR 30 switched on or conducting that a resonant circuit is formed between the primary of the ignition coil 26 and the storage capacitor 25. Thus, the L-C circuit formed will ring or resonant at its resonant frequency which is determined by the values of capacitance and inductance of the capacitor 25 and the primary of the coil 26, respectively. The L-C circuit formed continues to resonant as long as the SCR 30 is forward biased by the control signal applied to its gate electrode. Once the forward bias is removed from the SCR gate electrode, current will continue to flow in the circuit until the current through the SCR 30 drops below its regenerative or holding level. Once the SCR current drops below its regenerative level, it ceases to conduct since a control voltage sufficient to bias it into conduction is no longer applied to the SCR gate electroce. For further discussion of the operation of an L-C circuit having a SCR connected therein as a switch means, refer to assignee's earlier mentioned U.S. Pat. Application, Ser. No. 456,789, filed May 18, 1965.

The number of cycles the L-C circuit formed by the storage capacitor 15 and the ignition coil primary resonates or rings is determined by the time interval which the SCR 30 conducts. Likewise this time interval of SCR conduction determines the duration of the energy pulses supplied to the distributor 28 by the coil 26 and hence ignition spark durations. The control circuit 40 determines the time interval the SCR 30 is gated on by means of an R-C timing circuit formed by resistors 43, 45 and 46 and the capacitor 47. As above-mentioned, the charged points capacitor 49 causes a current to flow through the resistor 43. The current flow in the resistor 43 in turn progressively charges the capacitor 47, thereby inducing a rising current in the resistors 45 and 46. The resistors 45 and 46 function as a voltage divider for applying a bias voltage to the base electrode of the transistor 44 which functions as a control electrode and once a predetermined current level is induced in the resistors 45 and 46, a bias voltage sufficient to turn on or bias into conduction the transistor 44 is generated across the resistor 46. Once the transistor 44 conducts, a substantial portion of the current through the load resistor 50 is shunted to the return lead 19 through the collector-emitter path of the transistor 44. Thereby, the switch control voltage generated on the load resistor 50 and applied to the SCR gate electrode decreases from its first level which was sufficient to forward bias the SCR 30 to a second lower level which is not sufficient to forward bias the SCR 30. As before-mentioned, the SCR 30 then continues to conduct until the current level therethrough drops below the SCR's regenerative level at which time the SCR 30 turns off and ceases to conduct. Once the SCR 30 no longer conducts, the convertor 30 recommences operation and recharges the storage capacitor 25.

Subsequent to the switching off of the switching means provided by the SCR 30, the breaker contacts 48 are closed by engine movement. Upon closure of the points 48, the capacitor 49 discharges through the closed points 48 and the capacitor 47 discharges through the current paths provided by the resistor 43, points 48 and resistors 45, 46. After the points 48 have been closed for a sufficient time interval, the current through the resistor 46 drops below the level required to generate a voltage sufficient to forward bias the transistor 44. The transistor 44 thus turns off so as to allow subsequent retriggering of the SCR 40 at the next opening of the breaker points 48. It is noted that the SCR 30 will not be triggered into conduction by brief openings of the contacts 48 caused by contact bounce since the capacitor 47 provides a filtering effect. The capacitor 47 along with its associated resistors provides a time constant such that the points 48 must be closed for a sufficient time to discharge the capacitor 47 below the voltage required to turn on the transistor 44, i.e., the capacitor 47 must be discharged to the level at which transistor 44 becomes non-conductive before the current in the resistors 42 and 50 will be sufficient to forward bias the SCR 30. Thus, if the transistor 44 is not turned off, the SCR 30 will not conduct even if the points 48 are opened so that the ignition circuit is substantially insensitive to contact bounce. It should also be noted that capacitor 47 provides speed limiting of a motor. At low RPM, capacitor 47 discharges completely through resistor 43. At high speeds, capacitor 47 does not have sufficient time to completely discharge while points 48 are closed and by proper selection of the value of capacitor 47 the upper limit of the speed of a motor may be established above which capacitor 47 will not be permitted to discharge sufficiently to allow transistor 44 to become non-conductive and permit the SCR to be triggered into conduction. As one example, component values were selected to prevent conduction of the SCR at engine speeds above 8000 RPM to prevent damage to the engine.

As before mentioned, the control circuit 40 operates to control the time the SCR 30 is gated on as a function of the level of voltage of the battery 10, the rate the breaker contacts 48 are opened and closed, and the operating temperature of the ignition circuit and its associated engine. Thereby, the durations of the ignition sparks generated across the spark gaps 28 are controlled as a function of supply voltage level, engine speed and operating temperature. In order to explain the manner in which the control circuit 40 functions to control spark duration, reference is made to the graphs of FIGS. 2-5 in which the points designated A, B and C indicate, respectively, the instants when the SCR 30 is gated on, gated off and ceases to conduct.

Referring to FIG. 2, the graph there shown illustrates a typical wave form generated as a function of time across the primary of the ignition coil 26 with supply voltage, temperature and rate conditions normal or standard. A normal supply voltage is considered to be a voltage level of approximately 6 or 12 volts as supplied by the battery 10 to the control circuit 40 and the convertor 13. A normal operating temperature is considered to be the ambient temperature at which the ignition system is designed to operate. A normal rate is considered to be the rate at which the breaker contacts 48 are opening and closing as a result of engine movement when the engine is not being driven excessively fast. Under these normal conditions, the SCR 30 is biased into conduction at point A by opening of the contacts 48. The capacitor 25 and ignition coil 26 then resonate to generate a spark discharge across the gap 28 and the values of the circuit components making up the control circuit 40 are appropriately selected so that under such normal conditions the transistor 44 is turned on, and thus the SCR gate electrode is biased off, at the point designed B in FIG. 2. The SCR 30 continues to conduct until the point designated C at which instant the SCR current falls below the regenerative level. Thus, a spark duration equal to approximately two complete cycles of the resonant L-C circuit is generated across the spark gap 28 under normal supply voltage, temperature and rate conditions.

If the level of voltage supplied by the battery 10 decreases, the filter capacitor 25 will not be charged to as high a voltage level and consequently a longer spark duration is necessary to generate an ignition spark across the spark gap 28 having approximately the same amount of energy as a spark generated by the voltage wave form of FIG. 2. The control circuit 40 generates an ignition spark of longer duration, as shown in FIG. 3, since if the supply voltage is decreased, the current supplied through the resistor 43 to the capacitor 47 is correspondingly decreased. Thus, the capacitor 47 is charged more slowly with the result that SCR 30 is forwarded biased for a longer time since it takes a longer time interval for the current flowing from the capacitor 47 through the resistor 46 to reach the level necessary to bias the transistor 44 into conduction. As shown in FIG. 3, the voltage wave form across the primary of the ignition coil 26 has a smaller amplitude than that of FIG. 2 since the capacitor 25 is initially charged to a lower voltage due to the decreased voltage level supplied by the battery 10. As shown in FIG. 3, the transistor 44 is turned on to shunt the SCR gate electrode at the point designated B so that the L-C circuit generates an ignition spark of substantially three complete cycles of resonance as measured between points A and C in response to the voltage wave form of FIG. 3.

In the case where the engine associated with the ignition system is operated at an extremely high rate, the rate the points 48 are opened and closed is correspondingly increased. As a result of the rapid operation of the points 48, a higher than normal residual charge remains on the capacitor 47 due to the time constant provided by the values of the resistors 43, 45 and 46 and the capacitor 47. This increased residual charge results in a decreased time interval from the opening of the points 48 to the turning on of the transistor 44. Thus, the transistor 44 is turned on to shunt the SCR gate electrode at the point designated B in FIG. 4 so that an ignition spark having a duration of substantially only one complete cycle of the L-C circuit is generated in response to the voltage wave form of FIG. 4. Such a shorter spark duration is desirable since at high point operation rates long duration sparks waste energy, unduly stress ignition components and may prematurely fire the spark plugs of succeeding engine cylinders.

The graph shown in FIG. 5 illustrates the effect of low temperature on the ignition system. As the temperature is decreased, the forward bias point of the transistor 44, i.e., the voltage level necessary to be applied to the transistor's base electrode to turn the transistor on, increase. As a result of this voltage increase as a function of temperature decrease, the capacitor 47 must be charged to a higher level to turn on the transistor 44. Consequently, the SCR 20 is gated on for a longer interval so that a longer duration spark is generated which corresponds to the voltage wave form of FIG. 5. The wave form of FIG. 5 has a duration of substantially three cycles of resonance of the L-C circuit and it is desirable at low temperatures to generate long duration sparks since more energy is necessary to efficiently ignite and combust cold fuel.

It is noted that the relative effects of variations in supply voltage levels, temperature and rates of point operation may be varied and set as desired by the appropriate selection of the values of circuit components. While above the situations were discussed where only one of the variable conditions varied from the normal, it is noted that the voltage level, temperature and rate of point operation could all vary from the normal simultaneously and that depending on the specific conditions, ignitions sparks having durations of approximately 1/2 cycle, 1 cycle, 1 1/2 cycles, 2 cycles, 2 1/2 cycles, 3 cycles, etc., could be generated as appropriate by the exemplary ignition circuit. It further noted that various equivalent switching devices could be used for the SCR 30 and the transistor 44, e.g., an SCR could be used for the transistor 44. It should also be noted that a gating diode and resistors may be employed such that the charge and discharge times at capacitor 47 can be independently controlled.

Thus, there has been provided an improved ignition system which is operable to control ignition spark duration as a function of selected variable conditions. The ignition system is associated with a conventional engine of the type driven by ignition sparks and the spark durations are controlled as a function of engine speed as represented by the rate of breaker point operation, operating temperature as measured by a temperature sensitive switch means provided by a transistor and supply voltage level. An SCR switching means is provided for controlling the generation of ignition sparks which is operated by a control circuit in an extremely stable and reliable manner. Additionally, capacitors are connected across the ignition coil primary and the output of the control circuit to shunt and dissipate high frequency interference so as to prevent inadvertent generation of ignition sparks and insure stable operation of the SCR switch means, respectively.

While there have been described what is considered to be the preferred embodiment of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the present invention.

Claims

What is claimed is:

1. An ignition system for delivering pulses of energy of controlled durations to distributor means of an engine of the type having combustion chambers with a spark plug associated with each of said combustion chambers so that ignition sparks of controlled durations are generated across the spark gaps of said spark plugs to ignite combustible fuel delivered to said combustion chambers; said ignition system comprising:

a storage capacitor;

a charging circuit having input and output terminals, said charging circuit having its output terminals connected across said storage capacitor and being operable to charge said storage capacitor to a high potential D.C. voltage when a low potential D.C. voltage source is connected to its input terminals;

an ignition coil having primary and secondary windings, said ignition coil having its secondary winding connected to said distributor means;

timing means for generating a series of time signals corresponding to the movements of said engine;

control circuit means responsive to each of said time signals for generating a switch control signal, said control circuit means being operable to sense the level of D.C. voltage supplied to the input terminals of said charging circuit and generate switch control signals having durations which are a function of the level of said D.C. voltage supplied; and

switch means responsive to each of said switch control signals for connecting said storage capacitor in closed circuit with the primary winding of said ignition coil during a time interval substantially equal to the duration of said switch control signal whereby an L-C circuit is formed by said storage capacitor and the primary winding of said ignition coil which resonates during the time interval said storage capacitor and said primary winding are connected in closed circuit so that a pulse of energy of controlled duration is delivered by the secondary winding of said ignition coil to said distributor means to generate an ignition spark of corresponding duration.

2. The invention recited in claim 1, wherein said control circuit means is responsive to the rate at which said time signals are generated to generate switch control signals having durations which are also a function of the speed of said engine as measured by the rate at which said time signals are generated.

3. An ignition system for delivering pulses of energy of controlled durations to distributor means of an engine of the type having combustion chambers with a spark plug associated with each of said combustion chambers so that ignition sparks of controlled durations are generated across the spark gaps of said spark plugs to ignite combustible fuel delivered to said combustion chambers, said ignition system comprising:

a storage capacitor;

a charging circuit having input and output terminals, said charging circuit having its output terminals connected across said storage capacitor and being operable to charge said storage capacitor to a high potential D.C. voltage when a low potential D.C. voltage source is connected to its input terminals;

an ignition coil having primary and secondary windings, said ignition coil having its secondary winding connected to said distributor means;

a silicon controlled rectifier having anode, cathode and gate electrodes;

electrical leads connecting said storage capacitor, the primary winding of said ignition coil, and the anode-cathode path of said silicon controlled rectifier in a closed circuit so that said silicon controlled rectifier functions as a switch for controlling the operation of the L-C circuit formed by said storage capacitor and said primary winding;

breaker contact means associated with said engine for opening and closing in synchronism with the movements of said engine so as to generate a series of time signals corresponding to the time interval said contact means are open;

control circuit means responsive to each of said time signals for generating a control signal having a duration which is a function of the level of D.C. voltage supplied to the input terminals of said charging circuit, operating temperature and engine speed as represented by the rate at which said time signals are generated by said contact means, said control circuit means being connected to the gate electrode of said silicon controlled rectifier to supply said control signals generated thereto to bias said silicon controlled rectifier into conduction whereby the L-C circuit formed by said storage capacitor and the primary winding of said ignition coil resonates during the time interval said silicon controlled rectifier conducts so that a pulse of energy of controlled duration is delivered by the secondary winding of said ignition coil to said distributor means to generate an ignition spark of corresponding duration.

4. The invention recited in claim 3 including a load resistor in said control circuit means connected to the gate electrode of said silicon controlled rectifier and wherein said control circuit means is operable to generate said control signals applied to said gate electrode across said load resistor and said control circuit means includes:

switch means having a control electrode to which is applied a turn on voltage to bias said switch means into conduction, said switch means being temperature sensitive so that its turn on voltage varies as a function of temperature, said switch means being connected across said load resistor to shunt said load resistor whenever said switch means conducts; and

an R-C circuit means having terminals for connection to the same D.C. voltage source connected to the input terminals of said charging circuit whereby to sense and be driven by said same D.C. source, said R-C circuit means being connected to the control electrode of said switch means to supply bias voltage thereto, said R-C circuit means being operable to generate a bias voltage the magnitude of which increases at a rate directly proportional to the voltage level of said same D.C. source connected thereto for biasing said switch means into conduction whenever said bias voltage equals the turn on voltage of said switch means, said R-C circuit means being connected to said contact means for discharge of its capacitive portion through said contact means upon contact closure so that the residual charge remaining on said capacitive portion when said contact means reopens is a function of engine speed as represented by the rate said contact means are opened and closed.

5. The invention recited in claim 4 wherein said switch means is a transistor having its collector and emitter electrodes connected across said load resistor and its base electrode is said control electrode.

6. The invention recited in claim 5 wherein a parallel-connected choke coil and diode are connected in series with the anode-cathode path of said silicon controlled electrode to control the rate of current flow therethrough.

7. The invention recited in claim 6 including capacitive means for shunting electromagnetic interference are connected across the primary winding of said ignition coil and across said load resistor to enhance the reliability of said ignition system.

8. The invention recited in claim 7 wherein:

said charging circuit is a D.C.--D.C. convertor which includes a voltage transformer; and

said silicon controlled rectifier is connected to short the secondary winding of said voltage transformer to stop the operation of said charging circuit whenever said silicon controlled rectifier is conducting.

9. In a capacitor discharge type engine ignition system for delivering pulses of energy to the distributor means of a combustion engine wherein a storage capacitor is charged to a high potential by power supplied from a low potential D.C. source and first switch means are selectively operated to connect said storage capacitor in closed circuit with the primary of an ignition coil to form an L-C circuit so that said L-C circuit resonates to generate an ignition spark of duration corresponding to the interval of resonance across a spark gap connected by said distributor means across the secondary winding of said ignition coil, the improvement of:

breaker contact means associated with said engine for opening and closing in synchronism with the movements of said engine so as to generate a series of time signals corresponding to the time intervals said contact means are open;

circuit means responsive to said time signals and connected to said first switch means for generating first switch control signals during said time intervals and applying said first switch control signals to said first switch means to operate said first switch means;

second selectively operable switch means connected to shunt said first switch control signals away from said first switch means whenever said second switch means is conducting; and

R-c circuit means connected to said breaker contact means and said second switch means for generating second switch control signals during said time intervals to control the operation of said second switch means so that the operation of said first switch means is controlled by said second switch means and is substantially unaffected by any contact bounce of said breaker contact means.

10. An ignition system for delivering pulses of energy of controlled durations to distributor means of an engine of the type having combustion chambers with a spark plug associated with each of said combustion chambers so that ignition sparks of controlled durations are generated across the spark gaps of said spark plugs to ignite combustible fuel delivered to said combustion chambers; said ignition system comprising:

a storage capacitor;

a charging circuit having input and output terminals, said charging circuit having its output terminals connected across said storage capacitor and being operable to charge said storage capacitor to a high potential D.C. voltage when a low potential D.C. voltage source is connected to its input terminals;

an ignition coil having primary and secondary windings, said ignition coil having its secondary winding connected to said distributor means;

timing means for generating a series of time signals corresponding to the movements of said engine;

control circuit means responsive to each of said time signals for generating a switch control signal, said control circuit means being operable to sense the level of D.C. voltage supplied to the input terminals of said charging circuit and generate switch control signals having durations which are an inverse function of the level of said D.C. voltage supplied; and

switch means responsive to each of said switch control signals for connecting said storage capacitor in closed circuit with the primary winding of said ignition coil during a time interval substantially equal to the duration of said switch control signal whereby an L-C circuit is formed by said storage capacitor and the primary winding of said ignition coil which resonates during the time interval said storage capacitor and said primary winding are connected in closed circuit so that a pulse of energy of controlled duration is delivered by the secondary winding of said ignition coil to said distributor means to generate an ignition spark of corresponding duration.

11. An ignition system for delivering pulses of energy of controlled durations to distributor means of an engine of the type having combustion chambers with a spark plug associated with each of said combustion chambers so that ignition sparks of controlled durations are generated across the spark gaps of said spark plugs to ignite combustible fuel delivered to said combustion chambers; said ignition system comprising:

a storage capacitor;

a charging circuit having input and output terminals, said charging circuit having its output terminals connected across said storage capacitor and being operable to charge said storage capacitor to a high potential D.C. voltage when a low potential D.C. voltage source is connected to its input terminals;

an ignition coil having primary and secondary windings, said ignition coil having its secondary winding connected to said distributor means;

timing means for generating a series of time signals corresponding to the movements of said engine;

control circuit means responsive to each of said time signals for generating a switch control signal, said control circuit means being operable to sense engine operating temperature and generate switch control signals having durations which are an inverse function of said operating temperature sensed; and

switch means responsive to each of said switch control signals for connecting said storage capacitor in closed circuit with the primary winding of said ignition coil during a time interval substantially equal to the duration of said switch control signal whereby an L-C circuit is formed by said storage capacitor and the primary winding of said ignition coil which resonates during the time interval said storage capacitor and said primary winding are connected in closed circuit so that a pulse of energy of controlled duration is delivered by the secondary winding of said ignition coil to said distributor means to generate an ignition spark of corresponding duration.

12. An ignition system for delivering pulses of energy of controlled durations to distributor means of an engine of the type having combustion chambers with a spark plug associated with each of said combustion chambers so that ignition sparks of controlled durations are generated across the spark gaps of said spark plugs to ignite combustible fuel delivered to said combustion chambers; said ignition system comprising;

a storage capacitor;

a charging circuit having input and output terminals, said charging circuit having its output terminals connected across said storage capacitor and being operable to charge said storage capacitor to a high potential D.C. voltage when a low potential D.C. voltage source is connected to its input terminals;

an ignition coil having primary and secondary windings, said ignition coil having its secondary winding connected to said distributor means;

timing means for generating a series of time signals corresponding to the movements of said engine;

control circuit means responsive to each of said time signals for generating a switch control signal, said control circuit means including means for sensing engine operating temperature and being operable to generate switch control signals having durations which are a function of said engine operating temperature sensed; and

switch means responsive to each of said switch control signals for connecting said storage capacitor in closed circuit with the primary winding of said ignition coil during a time interval substantially equal to the duration of said switch control signal whereby an L-C circuit is formed by said storage capacitor and the primary winding of said ignition coil which resonates during the time interval said storage capacitor and said primary winding are connected in closed circuit so that a pulse of energy of controlled duration is delivered by the secondary winding of said ignition coil to said distributor means to generate an ignition spark of corresponding duration.

13. The invention recited in claim 12 wherein said means for sensing engine operating temperature is a temperature sensitive transistor.

14. An ignition system for delivering pulses of energy of controlled durations to distributor means of an engine of the type having combustion chambers with a spark plug associated with each of said combustion chambers so that ignition sparks of controlled durations are generated across the spark gaps of said spark plugs to ignite combustible fuel delivered to said combustion chambers; said ignition system comprising:

a storage capacitor;

a charging circuit having input and output terminals, said charging circuit having its output terminals connected across said storage capacitor and being operable to charge said storage capacitor to a high potential D.C. voltage when a low potential D.C. voltage source is connected to its input terminals;

an ignition coil having primary and secondary windings, said ignition coil having its secondary winding connected to said distributor means;

timing means for generating a series of time signals corresponding to the movements of said engine;

control circuit means responsive to each of said time signals for generating a switch control signal, said control circuit means being operable to sense the level of D.C. voltage supplied to the input terminals of said charging circuit and the engine operating temperature and generate switch control signals having durations which are inversely proportional to each of the variables the level of said D.C. voltage supplied, said engines operating temperature and the speed of said engine as measured by the rate at which said time signals are generated; and

switch means responsive to each of said switch control signals for connecting said storage capacitor in closed circuit with the primary winding of said ignition coil during a time interval substantially equal to the duration of said switch control signal whereby an L-C circuit is formed by said storage capacitor and the primary winding of said ignition coil which resonates during the time interval said storage capacitor and said primary winding are connected in closed circuit so that a pulse of energy of controlled duration is delivered by the secondary winding of said ignition coil to said distributor means to generate an ignition spark of corresponding duration.

15. A method of controlling the generation of ignition sparks across a spark gap in the combustion chamber of an engine which comprises:

charging a capacitor from a D.C. voltage source to a voltage proportional to the voltage level of said D.C. voltage source;

selectively commencing the discharge of said capacitor in timed relation with the movement of the engine to generate a series of timed spark across said spark gap;

controlling the length of each time period said capacitor is selectively discharged as a function of the voltage level of said D.C. voltage source, the speed of said engine and the operating temperature of said engine whereby to control the durations of the sparks generated across said spark gap.

16. The method of claim 15 wherein:

said capacitor is charged to a voltage directly proportional to the voltage level of said D.C. voltage source; and

the length of each time period said capacitor is selectively discharged is inversely proportional to each of the variables the voltage level of said D.C. voltage source, the speed of said engine and the operating temperature of said engine.