US 3832986 A
A capacitive discharge ignition system for providing an extended ignition coil output voltage duration includes main and auxiliary storage capacitors connected to an ignition coil. A charging oscillator provides charging current for both capacitors. A first SCR triggered by the engine points or magnetic breakerless assembly, discharges the main capacitor into the ignition coil. A timer circuit operable in response to the discharge of the main capacitor triggers the second SCR connected to the auxiliary capacitor and ignition coil after a predetermined time delay. The triggering of the second SCR discharges the auxiliary capacity into the ignition coil. The successive discharging of the main and auxiliary capacitors provides the increased ignition coil output voltage duration.
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Description (OCR text may contain errors)
United States Patent Dogadko [111 3,832,986 Sept. 3, 1974 CAPACITOR DISCHARGE IGNITION SYSTEM INCLUDING SPARK DURATION EXTENDER MEANS 3,728,991 4/1973 Montaschi 123/148 OCD Primary Examiner-Laurence M. Goodridge Assistant Examiner-Ronald B. Cox
 Inventor: Peter Dogadko, Chicago Attarney, Agent, or Firm--Donald J. Lisa; Vincent J.  Assignee: Motorola Inc., Franklin Park, Ill. Rauner  Fllfidi Dec. 14, 1972 57 ABSTRACT  Appl. No.: 315,267 A capacitive discharge ignition system for providing an extended ignition coil output voltage duration includes main and auxilia stora e ca acitors cong g 123/148 g xg nected to an ignition coilf A char ging :scillator prod 148 6 vides charging current for both capacitors. A first SCR 1 W 123mm) 1481a) triggered by the engine PQI IIS rraer kb 3kr19 assembly, discharges the main capacitor into the ignition coil. A timer circuit operable in response to the discharge of the main capacitor-triggers the second  References Clted SCR connected to the auxiliary capacitor and ignition UNITED STATES PATENTS coil after a predetermined time delay. The triggering 3,127,540 3/1964 Collins 123/148 0CD of the second SCR discharges the auxiliary capacity 3,202,874 8/1965 Bfil'dOCZ 123/148 0CD into the ignition coiL The uccessive discharging of sBtone the main and auxiliary capacitors provides the inarnes... 3,635,202 1/1972 Issler 123/148 0CD creased 'gnmon coll outputvoltage fiuranon' 3,669,086 6/1972 Beuk 123/148 MCD 8 Claims, 1 Drawing Flgure 10 h |BATT RY 56 1 TO 3/ BREAKER POINTS 53 5 IL on 5: MAGNETIC PICKUP 4 l 64 95 osc L A 0 cI R EuIT EL Eu- 74% E h 1 62 Iv IGNITION coII. /20 2 as 70 1. I T \\CAPACITIVE DISCHARGE Jrl/E 84V; IGNITION CIRCUIT a l y H4 f -$PARK DURATION 86 r EXTENDER CIRCUIT 2 I16 98 ,TIMER k/00| I08 CIRCUIT ["5111 I I I12 R l I02 I 1y I J CAPACITOR DISCHARGE IGNITION SYSTEM INCLUDING SPARK DURATION EXTENDER MEANS BACKGROUND This invention relates generally to electronic ignition systems for automotive vehicles and more particularly to capacitive discharge ignition systems.
As the automotive industry becamefaced with more rigid anti-pollution standards, they turned to electronic ignition systems as a means for decreasing pollution and to increase the performance of an internal combustion engine in a vehicle.
ln selecting an ignition system for use in vehicles, the highly desirable capacitive discharge ignition system was put aside in favor of other solid state systems, some of which use bulky ballast resistors, may require a heavy battery chain and which have high speed limitations. One of the reasons for the decision to use these other systems rather than the capacitive discharge ignition system, is the ability in the first-mentioned systems to obtain a spark of longer duration with a conventional ignition coil than could be provided by the capacitive discharge ignition system. The spark duration provided by these systems is roughly 1.2 milliseconds, while with a conventional capacitive discharge ignition system the spark duration is on the order of 0.4 milliseconds.
With the shorter spark duration of the capacitive discharge ignition system, spark plugs of the engine in which the system is used have a longer life,'but it is more difficult to start the engine in colder weather and timing becomes more critical.
lf the spark duration in a capacitive discharge ignition system could be increased from 0.4 milliseconds to within a range of 0.75 to 0.9 milliseconds to overcome the short spark duration problems, the capacitive discharge ignition system would out perform the conventional transistorized system in so far as being more efficient, providing a more constant voltage output, having a higher speed capability and providing longer spark plug life, and yet overcome the starting and timing problems associated therewith.
SUMMARY Accordingly, it is a primary object of the present invention to provide a new and improved capacitive discharge ignition system which has a longer spark duration than conventional capacitive discharge ignition systems.
It is yet another object of the invention to provide circuitry for use with a conventional capacitive discharge ignition system which extends the duration of the spark therein to avoid'the drawbacks of conventional capacitive discharge ignition systems having shorter spark durations.
lt is still another object of the present invention to provide a new and improved capacitive discharge ignition system of the above described type which has all of the attributes of a conventional capacitive discharge ignition system and which avoids substantially the limitations of such a system as described heretofore.
Briefly, a preferred embodiment of a capacitive discharge'ignition system according to the invention includes a storage capacitor which is initially charged. An auxiliary capacitor in a spark duration extending or lengthening circuit is also charged with the main stor- 2 age capacitor. Thereafter, a triggering pulse provided by points or a magnetic breakerless arrangement operates a first silicon controlled rectifier to discharge the main capacitor into the ignition coil. The discharge provides a transistor of a blocking oscillator employed initially to charge the capacitors, with base bias. The emitter voltage of the lastmentioned transistor thereby provides a signal to operate a timer circuit in the spark duration lengthening circuit. The timer circuit, after a 0.4 millisecond delay, triggers a second silicon controlled rectifier in the auxiliary circuit, to in turn, dis charge the auxiliary capacitor into the ignition coil. The additional energy from the auxiliary capacitor subsequent to the 0.4 millisecond delay, provides an in crease in spark duration of approximately 0.350 milliseconds, depending on the size of the auxiliary capacitor and the timer circuit.
trated a schematic diagram of the improved capacitive discharge ignition system including spark duration extender circuitry according to the invention. 7
DETAILED DESCRIPTION Referring now to the single FIGURE of the drawing, there is illustrated therein a capacitor discharge ignition system for an automotive vehicle according to the invention, designated generally by the numeral 10. The ignition system includes a capacitive discharge ignition circuit portion and spark duration extender circuit portion, each of which is outlined in dashed lines.
The capacitive discharge ignition circuit portion of the ignition system comprises an oscillator circuit, including a transistor 18 having base, emitter and collector electrodes 20, 22, 24, respectively. The base electrode 20 is connected through a bias resistor 26 to junction 28 whereat a capacitor 30 and parallel diode resistor combination 32 are connected. The lastmentioned combination is also connected to the secondary 34 of a transformer 36; the primary 38 of the transformer being connected to the emitter 22 of the transistor 18. The collector 24 of transistor 18 is connected via lead 40 through a reverse polarity protecting diode 42 and an ignition switch 44 to the vehicle battery (not shown).
Capacitor 30.is also connected over lead 46 to the emitter 48 of a second transistor 50 of the capacitive discharge circuit portion 12. A resistor 47 is connected between the emitter 48 of transistor 50 and lead 40, and a capacitor 49 is coupled between lead 40 and ground potential. The transistor 50 includes base and collector electrodes ,52, 54, respectively, the latter of which is connected to ground potential. The base electrode 52 of transistor 50 is connected through a transient protecting diode 56 and resistor 58 to circuitry in cluding the system storage capacitor 60.
The last-mentioned circuitry includes a transformer winding 62 coupled inductively to the transformer 36. Connected in series with the winding 62 is a silicon controlled rectifier switch 64, the primary 66 of ignition coil 68 of the system and diodes 70, 72. Capacitor is connected across the output winding 62 along with a free wheeling diode 74 which permits continued current flow in the ignition coil subsequent to. the discharge of the capacitor 60, and a transient protecting device 76. The secondary 78 of the ignition coil is coupled to a distributor (not shown).
The controlled rectifier switch 64 includes a control electrode 80 which is connected through a transformer 82 to the breaker points or magnetic pickup (not shown) of the system which provides a trigger pulse to operate the silicon controlled rectifier to an on conditron.
Connected to the capacitive discharge ignition circuit portion of the system 10, is a spark duration extender circuit portion. The last-mentioned circuit portion includes an auxiliary storage capacitor 84 connected at one terminal at junction 86 to the main storage capacitor 60, and at the other terminal at junction 88 whereat the cathode of a diode 90 and anode of a second silicon controlled rectifier switch 92 is also connected. The anode of the diode 90 is coupled over lead 94 to one side of winding 62 and the cathode of the silicon controlled rectifier 92 is coupled at junction 96 to the cathode of silicon controlled rectifier 64. Gate electrode 98 of the silicon controlled rectifier 92 is coupled through a transformer to a programmable unijunction transistor (PUT) 102 forming a portion of a timing circuit, including also, capacitor 106 connected between ground potential and junction 108 whereat the anode of the PUT and a resistor 110 are also connected. The control electrode 112 of the PUT 102 is coupled through a voltage divider network including resistors 114, 116, and a diode 118 and over lead 120 to one side of the primary winding 34 of transformer 36 of the blocking oscillator 16.
In operation, the ignition switch 44 is closed initially to provide power from the storage battery to the capacitive discharge ignition system for initiating operation thereof. A high voltage spike produced normally by the closing of the ignition switch 44 is usually sufficient to bias transistor 18 to the on condition to begin the ignition cycle. In the event the high voltage spike is not present, most likely due to the abnormally slow closing of the ignition switch, transistor 50 insures the initiation of the cycle.
In the last-mentioned case, current from the battery charges capacitor 30 slowly through resistor 47. At this time, while cranking the engine, a trigger signal is provided from the magnetic pickup or points to the control electrode 80 of silicon controlled rectifiers (SCR) 64 to turn the last-mentioned component on. Turning on SCR 64 provides a ground potential at the base electrode 52 of transistor 50 to turn the transistor on also. The turning on of transistor 50 discharges capacitor 30 and the SCR 64 turns off due to the high values of resistors 47 and 58 which limit current to the SCR below that required to hold it on. With SC R 64 off, the ground at base 52 of transistor 50 is removed and the latter is also turned off.
At this point in time, the emitter 48 of transistor 50 is at the potential of the vehicle storage battery and capacitor 30 is once again charged through resistor 47. Current flowing through the capacitor 30 provides base bias to transistor 18 of oscillator circuit 16 thereby to turn the transistor on.
Once transistor 18 is turned on, either by the initial high voltage spike from the closing of ignition switch 44 or through the operation of transistor 50 as described heretofore, the ignition cycle has been initiated.
Transistor l8 stays on so long as capacitor 30 is charging. Upon capacitor 30 being fully charged, the
bias on transistor base 20 of transistor 18 is removed to turn the last-mentioned transistor off. During the operation of transistor 18, current was flowing through emitter 22 and the winding 38 to ground. At the time the transistor is turned off, a high voltage appears at the winding 38 and is inductively coupled to winding 62 to produce a current flow therethrough for charging the main storage capacitor via diode 72, and auxiliary capacitor 84 of the spark duration extender circuit portion through diodes and 72 with the polarities as shown in the drawing.
A subsequent trigger signal from the ignition points or breakerless pickup, via transformer 82 to control electrode 80 of SCR 64, operates the latter to complete a series circuit including capacitor 60, SCR 64, the primary 66 of ignition coil 68 and forward biased diode 70 to discharge capacitor 60 into the ignition coil for provision of a spark via the vehicle distributor (not shown).
During the discharge of capacitor 60, the variation in current through winding 62 induces a voltage back into coil 38 of transformer 36 which is passed to the primary winding 34 and to base 20 of the transistor 18, to turn the last-mentioned transistor on. The operation of transistor 18 provides a voltage across winding 34 to produce a current on lead 120 for operating the timer circuit of the spark duration extender circuit portion. Capacitor 106 of the timer circuit is charged until the voltage at junction 108 is greater than the divided down voltage at the gate electrode 112 of PUT 102, thereby rendering the lastmentioned component conductive. Normally, the delay in operating PUT 102 is on the order of 0.4 milliseconds, sufficient to permit capacitor 60 to be discharged. Subsequent to the operation of PUT 102, transistor 18 is rendered non-conductive. The time it takes transistor 18 to return to an off or non-conductive state is sufficiently longer than the time it takes to turn PUT 102 on.
When PUT 102 is turned on, a trigger signal is provided by the discharge of capacitor 106 therethrough, through transformer to gate electrode 98 of SCR 92 to turn the last-mentioned component on. Turning on SCR 92 completes a circuit including auxiliary capacitor 84, SCR 92, the primary 66 of ignition coil 68 and diode 70, to discharge the auxiliary capacitor into the ignition coil. The discharging of capacitor 84 thereby extends the spark duration initiated by the discharge of capacitor 60. The spark duration is increased by approximately 0.350'milliseconds.
Subsequent to the full discharge of capacitor 84 into the ignition coil, SCR 92 is rendered non-conductive. Upon the turning off of transistor 18, a high voltage is induced from winding 38 of transformer 36 into winding 62 to once again charge capacitors 60 and 84 and to repeat the cycle.
Thus, the circuit according to the invention provides a capacitive discharge ignition system which has the attributes of a conventional capacitive discharge ignition circuit, as well as a sufficiently long-spark duration to provide better engine starting in cold weather and to lessen the criticality of timing of the engine with which the capacitive discharge ignition system is used.
While a particular embodiment of the invention has been shown and described, it should be understood that the invention is not limited thereto since many modifications may be made. It is therefore contemplatedto cover by the present application any and all such modifications as fall within the true spirit and scope of the appended claims.
1. In a capacitive discharge ignition system for use with an internal combustion engine, including a main storage capacitor, an ignition coil coupled electrically to said storage capacitor for providing ignition output voltage for operating the engine, means coupled electrically to said storage capacitor for charging said capacitor, means for producing trigger pulses in accordance with the operation of the engine and controlled switch means coupled electrically to said pulse trigger means and said storage capacitor for operation in accordance with the receipt of a pulse from said trigger means to discharge said storage capacitor into said ignition coil, spark duration extending circuit means including in combination: an auxiliary capacitor coupled electrically to said ignition coil and to said charging means and being charged by said last-mentioned means, a second controlled switch means connected electrically to said auxiliary capacitor for discharging the last-mentioned capacitor in accordance with the operation of said second controlled switch means, oscillator circuit means inductive means coupling said oscillator circuit means to said main and auxiliary capacitors and timer circuit means coupled electrically to said oscillator circuit means and to said second controlled switch means, said oscillator circuit means being operated in response to the receipt of a voltage inductively provided upon the discharge of said maincapacitor, said oscillator means thereby providing a signal to said timer circuit means, said timer circuit means being operable in response to the receipt of said signal from said oscillator circuit to operate said second controlled switch means for discharging said auxiliary capacitor into said ignition coil, said timer circuit means including delay means having a predetermined delay period for delaying the discharge of said auxiliary capacitor a predetermined time after the initiation of the discharge of said main storage capacitor thereby to extend the duration of the ignition output voltage of said ignition coil,
2. A capacitive discharge ignition system as claimed in claim 1 wherein said oscillator circuit means comprises said charging means and wherein said oscillator circuit means is operable between an on and off condition, said oscillator circuit means being operable between said on and off condition firstly for inductively charging said main and auxiliary capacitors and secondly, upon discharge of said main capacitor, for operating said timer circuit means and for recharging said capacitors.
3. A capacitive discharge ignition system as claimed in claim 1 further including ignition switch means operable between actuated and unactuated positions, and
connected electrically to a source of power, and
4. A capacitive discharge ignition system as claimed in claim 3 wherein said timer circuit means is coupled electrically to said transformer means and wherein upon discharge of said main storage capacitor, a voltage is induced in said transformer means to operate said solid state switch means to provide current to said timer circuit means for operation thereof.
5. A capacitive discharge ignition system as claimed in claim 4 wherein said timer circuit means of said spark duration extender circuit includes solid state switch means and capacitor means coupled thereto, said capacitor means being charged in response to current from said charging means upon discharge of said main storage capacitor, said capacitor means having a predetermined charging time, said solid state switch means being operable to an on condition in response to the charging of said capacitor means, thereby to dis charge said capacitor means for operation of said second controlled switch means.
6. A capacitive discharge ignition system for use with an internal combustion engine, including in combination; a main storage capacitor, an auxiliary storage capacitor, an ignition coil coupled electrically to said main and auxiliary capacitors for providing a high voltcoupled electrically to said main and auxiliary capacitors, said charging means being operable to charge said capacitors, trigger pulse means operable to provide periodic trigger pulses in accordance with the operation of said engine, first switch means connected to said main storage capacitor and to said trigger pulse means and operable in response to the receipt of a pulse from said trigger pulse means to discharge said main storage capacitor into said ignition coil, second switch means connected to said auxiliary capacitor and to said ignition coil, and timer circuit means coupled electrically to said system and to said second switch means, said timer circuit means being operable in response to the discharge of said main storage capacitor to operate said second switch means for discharging said auxiliary capacitor into said ignition coil, said timer circuit means having a delay period for delaying the operation of said second switch means for a predetermined time whereby said auxiliary capacitor is discharged in succession with said main storage capacitor to extend the duration of output voltage from said ignition coil, wherein said charging means includes oscillator circuit means having first winding means, and second winding means connected to said main and auxiliary capacitors, said oscillator circuit means being inductively coupled by means of said first winding means and said second winding means to said main and auxiliary capacitors, and wherein said timer circuit means is connected electrically to said oscillator circuit means, whereby upon operation of said last-mentioned circuit means between an on and off condition, charging voltage is provided inductively via said first and second winding means, respectively, for charging said capacitors and upon discharge of said main storage capacitor, a return voltage is inductively provided through said second winding means and first winding means of said oscillator circuit means, respectively, to operate said oscillator circuit means between an on and off condition, said oscillator circuit means in response thereto providing a signal to said timer circuit for the operation thereof 7. A capacitive discharge ignition system as claimed in claim 6 wherein said timer circuit means includes a 8. A capacitive discharge ignition system as claimed in claim 7 wherein said first and second switch means each comprise a silicon controlled rectifier and wherein said controlled switch means of said timer circuit means include a programmable unijunction transistor.