US3584929A - Spark duration for capacitor discharge ignition systems - Google Patents

Abstract

A capacitor discharge ignition system wherein an energy storage capacitor is charged to a relatively high voltage and synchronously discharged into the primary winding of an ignition coil to develop a high-energy short-time duration spark discharge at the secondary winding of the ignition coil, and a circuit is provided for increasing the time duration of the spark discharge beyond that normally obtained from the capacitor discharge system to improve the fuel-igniting properties of the spark.

Description

United States Patent Inventor Gunter G. Schuette Addison, I11. Appl. No. 888,782 Filed Dec. 29, 1969 Patented June 15, I971 Assignee Motorola Inc.

Franklin Park, Ill.

SPARK DURATION FOR CAPACITOR DISCHARGE IGNITION SYSTEMS 7 Claims, 4 Drawing Figs.

U.S. Cl 315/244, 315/206, 317/96, 320/1, 307/106 Int. Cl 1105b 41/14 Field of Search 317/79, 80, 96;315/183, 187, 200, 206, 209, 241, 244, 289; 307/106; 320/1 [56] References Cited UNITED STATES PATENTS 2,799,809 7/1957 Lautenberger 317/79 3,045,148 7/1962 McNulty et al. 315/183 3,255,366 6/1966 McNulty et a1. 307/106 3,336,506 8/1967 Frank 317/96 3,417,306 12/1968 Knak 320/1 3,457,456 7/1969 Dietz 315/206 Primary Examiner-Velodymyr Y. Mayewsky Attorney-Mueller, Aichele & Rauner ABSTRACT: A capacitor discharge ignition system wherein an energy storage capacitor is charged to a relatively high voltage and synchronously discharged into the primary winding of an ignition coil to develop a high-energy short-time duration spark discharge at the secondary winding of the ignition coil, and a circuit is provided for increasing the time duration of the spark discharge beyond that normally obtained from the capacitor discharge system to improve the fuel-igniting properties of the spark.

PATENTEUJUNISIH?! 35 4,5329

SHEET 1 [IF 2 UNCONTROLLED DISC HARGED FIGZ CONTROLLED DISCHARGE INVENTOR GUNTER G. SCHUETTE 441M WW ATTORN EYS.

SPARK DURATION FOR CAPACITOR DISCHARGE IGNITION SYSTEMS BACKGROUND OF THE INVENTION This invention relates generally to ignition systems of the type producing a high-voltage low-current energy pulse at the primary winding of an ignition coil, and more particularly to an improved capacitor discharge ignition system.

Capacitor discharge ignition systems, that is, systems which utilize capacitors for intermittently discharging a relatively high-voltage energy pulse through the primary winding of an ignition coil, have found relatively widespread and popular use in connection with internal combustion engines. Such capacitor discharge ignition systems have several advantages over conventional Kettering ignition systems. One advantage is that the power drain from the automobile battery is substantially reduced when using a capacitor discharge ignition system. Another advantage of capacitor discharge ignition systems is that a spark of higher voltage, i.e., higher fuel-igniting properties, can be generated more readily with a somewhat rundown storage battery connected thereto, than .could otherwise be obtained by a conventional ignition system. Yet another advantage obtained from capacitor discharge ignition systems is that the spark potential generated at spaced-apart electrodes within a spark plug remains substantially constant over a much wider range of engine speeds than otherwise can be obtained from the conventional ignition 1 systems.

Although capacitor discharge ignition systems have improved operating characteristics, they produce a spark discharge having a time duration much less than that produced by a conventional Kettering ignition system. Despite the fact that the voltage of the spark discharge is substantially increased, and remains so over a much wider range of engine speeds, it has been found that the fuel-igniting properties of the high-voltage short-duration spark discharge is somewhat limited under certain conditions. For example, although fuelair mixtures of the proper ratio are readily ignited in a reliable and repeatable fashion from the spark discharge of a capacitor discharge ignition system and the high-voltage spark generally has sufficient fuel-igniting properties to ignite fuel mixtures which are slightly off the desired fuel-air mixture ratio, the fact is with a substantial abnormality of the desired fuel-air mixture the capacitor discharge ignition systems heretofore provided may have difficulty in initiating combustion of the fuel-air mixture within a given cylinder of an internal combustion engine. Also, because of the short duration of the spark discharge produced by capacitor discharge ignition systems, it is generally an important requirement that the proper air-fuel mixture withinthe cylinder of the engine be located substantially in the vicinity of the spaced-apart electrodes of the spark plug so that the spark discharge will heat and ignite the fuel mixture in this vicinity. However, the random mobility of a given quantity of molecules of a fuel-air mixture may cause the vicinity around the spaced-apart electrodes to be vacant of sufficient fuel-air mixture during the short-duration spark discharge, this problem being particularly acute in cold weather.

SUMMARY OF THE lNVENTlON It is therefore an object of this invention to provide a capacitor discharge ignition system which overcomes the problems set forth hereinabove, and which is efficient and reliable in operation and inexpensive to manufacture.

Another object of this invention is to provide a capacitor discharge ignition system which will create a high-voltage spark discharge at spaced-apart electrodes for an increased time duration.

Briefly, the capacitor discharge ignition system of the illustrated embodiment includes a storage capacitor for receiving and storing a high-voltage energy pulse which is to be discharged into the primary winding of an ignition coil in synchronism with external pulse signal information. The external pulse signal information may be generated by, for example, the opening of a mechanical breaker-point assembly, an electrical impulse developed by a light-emitting pulsating source. An energy supply circuit is coupled to the energy storage capacitor to deliver thereto a high-voltage electrical energy pulse substantially immediately after a previous energy pulse has been discharged from the capacitor through the primary winding of the ignition coil. The discharge of the energy storage capacitor is accomplished by a series-connected current control device, such as a silicon-controlled rectifier, which serves as a fast-acting switch. Most advantageously, means are provided in circuit with the current control device and arranged for connection to the primary winding of the ignition coil to provide a sustained energy transfer condition at the primary winding or, in the alternative, to provide additional energy thereto. That is, the means connected in circuit with the current control device is effective substantially immediately in response to the discharge of the energy storage capacitor to extend the duration of the current flow through the primary winding of the ignition coil beyond that of the normal time duration. This action increases the time duration of the spark discharge at the secondary winding of the ignition coil to greatly improve the spark-igniting properties of the spark discharge which, in turn, will enhance the starting capability ofan internal combustion engine.

In one embodiment of this invention an inductor is placed in series between the current control device, which discharges the energy storage capacitor, and the primary winding of the ignition coil. The inductance value of the inductor is selected so that when combined with the inductance value of the primary winding of the ignition coil the total inductance thereof will provide an inductive reactance preferably approximately equal to the capacitive reactance of the energy storage capacitor for a given frequency. The time duration of one-half cycle of this given frequency is then selected to be the approximate time duration of an energizing current pulse through the primary winding of the ignition coil and, because of the tight coupling of the ignition coil between its primary and secondary windings, is also the approximate time duration of the spark discharge produced at the secondary winding. It should be understood that the inductive reactance is to be determined during the spark discharge at the secondary winding of the ignition coil and not during conditions of no spark discharge. Therefore, only during the spark discharge at the spaced-apart electrodes will the energy storage capacitor, and the inductance offered by the primary winding of the ignition coil, and the added inductance connected in series therewith, act as a resonant circuit substantially to increase the time duration of the spark discharge. This increased time duration of the spark discharge will have a desirable affect on the starting capabilities of an internal combustion engine.

In another embodiment of the illustrated invention means are provided to apply additional current flow through the primary winding of the ignition-coil to commence substantially immediately after the discharge of the energy storage capacitor or upon substantial discharge thereof. This additional current flow causes an aiding magnetic field to be developed within the ignition coil during the period of time when a spark discharge is established across the spaced-apart electrodes of a spark plug. This additional current flow will establish a spark discharge for a period of time similar to that provided by adding an additional inductance in series with the primary winding of the ignition coil, as mentioned hereinabove. Preferably, the additional current flow to the primary winding of the ignition coil is provided by a current control device which is triggered to its low-resistance current-conducting condition in response to the discharge of the energy storage capacitor. The current control device remains conductive until the energy storage capacitor is again being charged with a subsequent energy pulse in readiness to again be discharged into the primary winding of the ignition coil.

Most advantageously, the current control device is a siliconcontrolled rectifier having its gate electrode connected to its anode through a resistor of a given predetermined resistance value which is selected to cause firing of the silicon-controlled rectifier at the precise moment in time. When the circuit arrangement of this inventionis used in conjunction with a capacitor discharge ignition system which utilizes a single swing-blocking oscillator to apply energy pulses to the energy storage capacitor, the silicon-controlled rectifier which supplies the additional current to the primary winding of the ignition coil is commutated to an off condition by a reversal of voltage which is generated within the single swing-blocking oscillator. However, it will be understood that the broad and novel conceptsof this invention can be used in connection with capacitor discharge ignition systems of various kinds and that commutation to an off condition of the silicon controlled rectifier which supplies the additional current can be accomplished by any suitable and well-known means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing the essential portions of a capacitor discharge circuit illustrating one embodiment of this invention;

FIG. 2 is a graphical representation of a high-voltage spark discharge generated at the spaced-apart electrodes of FIG. 1 showing both the uncontrolled short duration discharge of a conventional capacitor discharge ignition system and an extended, controlled discharge of the capacitor discharge ignition system incorporating the features of this invention;

FIG. 3 is a schematic diagram illustrating still another embodiment of this invention wherein means are provided for applying additional current through the primary winding of the spark coil substantially immediately after the rapid discharge of the energy storage capacitor;

FIG. 4.illustrates a series of waveforms at various circuit points within the circuit of FIG. 3.

. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. I there is seen the essential portion of the capacitor discharge circuit required for a complete understanding of the present invention, and designated generally byreference numeral 10. Here, anenergy storage capacitor 12 is connected across asecondary winding 14a of atransformer 14, the other windings thereof not being shown and are of any suitable configuration. Connected in series with thecapacitor 12 andsecondary winding 14a is adiode 16 which serves to provide a blocking element in series with thecapacitor 12 and secondary winding 14a so that the charge oncapacitor 12 remains until discharged into a primary winding 18a of anignition coil 18. The energy pulse oncapacitor 12 is delivered to the primary winding 18a through a current control device, here illustrated as the silicon-controlledrectifier 20, whichacts as a switch in response to external pulse signal information applied to a pulse-formingtransformer 22.

Most advantageously, aninductance element 24 is connected in series with the silicon-controlledrectifier 20 and the primary winding 18a of theignition coil 18 and serves to extend the time duration of a spark discharge developed between spaced-apart electrodes 26, which may be the spark gap in one or more spark plugs of an internal combustion engine. The high-voltage spark discharge at thespark gap 26 is delivered thereto by a secondary winding 18b of theignition coil 18. Upon discharge of capacitor 12 a slight current flow will pass through adiode 28 which has its cathode connected to the juncture ofcapacitor 12 anddiode 16, in a well-known manner.

The inductance value of theinductance element 24 is preferably selected so as to assist in sustaining current flow through the primary winding 18a oftheignition coil 18 during the period of time when a spark discharge exists between the spaced-apart electrodes 26. Preferably, the inductance value of theinductance element 24 is selected so that when added with the inductance value of theprimary winding 180 they combine to provide an inductive reactance approximately equal to the capacitive reactance of theenergy storage capacitor 12 at a given frequency; This provides a resonant circuit betweencapacitor 12,inductance element 24 and primary winding 18a during the period of time when the silicon-controlledrectifier 20 is conductive and a spark discharge has been initiated between the spaced-apart electrodes 26. In one arrangement it was found that an inductance value of 30 millihenrles provided good results when used with an Ignition coll having a primary winding Inductance of approximately 9.3 millihenries. The improved spark duration is best illustrated in FIG. 2 wherein the short-duration uncontrolled spark discharge obtained from a conventional capacitor discharge ignition system is designated by reference numeral 26a, and the increased duration controlled spark discharge obtained from the circuit of FIG. 1 is designated byreference numeral 26b.

To prevent ringing oscillations within the primary winding 18a adiode 30 is connected in parallel with the primary winding and theinductance element 24, this diode being rendered conductive upon the reversal of voltage across theinductance element 24 and the primary winding 18a. Aprotection device 32 is connected in parallel with thediode 30 and serves to prevent reverse voltage breakdown of thediode 30. Theprotection device 32 preferably is a bidirectional thresholdersswitching device, but it may be any suitable voltage-dependent resistance element having a characteristic which will prevent excess voltage from appearing across thediode 30.

Referring now to FIG. 3 there is seen an alternate arrangement of this invention wherein the spark duration at the spaced-apart electrodes 26 is sustained beyond that normally obtained from a capacitor discharge ignition system by providing additional current flow through the primary winding 18a by means of acurrent duration circuit 40. Preferably, the cur- 'rent duration circuit 40 comprises a current control device,

such as a silicon-controlled rectifier 42, which has its gate electrode 42a connected to itsanode 42b by means of aresistor 44. The resistance value of theresistor 44 is selected to cause the silicon-controlled rectifier 42 to be rendered conductive at a point in time substantially immediately following the discharge ofcapacitor 12 into the primary winding 18a of theignition coil 18. It should be noted that in this embodiment theinductance element 24 may be eliminated.

Battery potential, for example, that provided by the battery of an automobile, is applied to acircuit point 46 and to theanode 42b of the silicon-controlled rectifier 42 through a power-switchingtransistor 48 which forms a single swingblocking oscillator with thetransformer 14. The emitter electrode oftransistor 48 is also connected to a pair ofprimary windings 14b and 140 of thetransformer 14 which form a stepup transformer with respect to thesecondarywinding 14a, and primary winding 140 also serves as a feedback loop to the base electrode oftransistor 48 through a parallel network including aresistor 50 and adiode 52 connected in series with another resistor54. The feedback network from primary winding 14c serves as a regenerative feedback loop to causetransistor 48 rapidly to become conductive to a saturated condition to apply a current pulse to the primary winding 14b and upon sensing a reduction of the rate of change of the magnetic field within thetransformer 14 also serves rapidly to render atransistor 48 nonconductive. The single swing blocking oscillator formed bytransistor 48 andtransformer 14 applies an energy pulse to theenergy storage capacitor 12 which is then discharged into the primary winding 18a oftheignition coil 18 by means of the silicon-controlledrectifier 20. As seen in FIG. 4, the curve 60 represents the emitter voltage oftransistor 48 as taken from the circuit point connected to theprimary windings 14b and Me of thetransformer 14. At the point in time t,transistor 48 is rendered conductive as indicated by reference numeral 600. This point in time corresponds to the discharge ofcapacitor 12 as indicated by the energy pulse applied to the primary winding 18a and is illustrated by thecurve 62 which is a high-voltage pulse rapidly decreasing to aslight depression 620 within thecurve 62. It is this discharge of thecapacitor 12 which causestransistor 48 to be rendered conducive as illustrated by the curve 60. However, it will be noted that conduction oftransistor 48 also applies battery potential to theanode 42b of the silicon-controlled rectifier 42 to apply additional current through the primary winding 18a as illustrated by thelinear portion 62b of FIG. 4. The regenerative cutoff voltage developed intransformer 14 is applied to the emitter electrode oftransistor 48, as indicated by thecurved portion 60b of FIG. 4 to rendertransistor 48 nonconductive which, in turn, removes the battery potential from the siliconcontrolled rectifier 42 to terminate the additional current flow through primary winding 18a, as indicated by .therapid cutoff portion 62c of thecurve 62.

Here, the spark discharge between the spaced-apartelectrode 26 is illustrated by thecurve 64. A slight ringing action indicated by the series of curves 6411- which are contiguous with thecurve 64 represent the tendency of theignition coil 18 to cause diminishing of the spark discharge duration along the dotted curve 66, which indicates the normal discharge path of a conventional capacitor discharge ignition system. However, because of the added current flow through the primary winding 18a which is transformer coupled to the secondary winding at a point in time when a spark discharge is already established, the short-duration pulse which would ordinarily occur, as indicated by the dotted curve 66, is extended into a long-duration pulse indicted by thecurve 64,

and the advantageous results of this invention are obtained.

FIG. 3 also illustrates adiode 68 connected in parallel with the primary winding of the pulse-formingtransformer 22 which serves to reduce kickback voltage from occurring in the transformer, and aresistor 70 is connected in series with the primary winding-of thepulse transformer 22 to apply the operating potential thereto when a breaker-point assembly, no shown, is in the closed circuit condition. The opening of the breaker-point assembly applies a trigger pulse to the gate cathode circuit of silicon-controlled rectifier in a conventional and well-known manner to render the same conductive. Accordingly, when using either of the illustrated embodiments disclosed herein, the novel concepts of this invention provide means for substantially increasing the time duration of a spark discharge created between spaced-apart electrodes when such spark is generated from a capacitor discharge ignition system. lclaim: l. A capacitor discharge ignition system for generating spark-producing potentials at the primary winding of an ignition coil so that a spark discharge is produced between electrodes connected to the secondary winding thereof, comprismg:

an energy storage capacitor for receiving and storing a highvoltage electrical energy pulse; an energy supply circuit coupled to said energy storage capacitor for delivering thereto a high-voltage electrical energy pulse substantially immediately after a previous energy pulse has been discharged therefrom and applied to the primary winding of the ignition coil;

control-switching means connected to said energy storage capacitor and arranged for connection to the primary winding of the ignition coil;

external pulse signal information means coupled to said control-switching means to render the same conductive in response thereto substantially instantaneously to discharge said energy storage capacitor into the primary winding of the ignition coil within a relatively short predetermined time interval to initiate a spark discharge between the electrode connected to the secondary winding; and

means connected in circuit with said control-switching means and arranged for connection to the primary winding of the ignition coil, said means being substantially immediately responsive to the discharge of said energy storage capacitor to extend the duration of current flow through the primary winding of the ignition coil beyond that of said relatively short predetermined time interval to increase the duration of the spark discharge produced between the electrodes connected to the secondary winding thereof. 7

2. The capacitor discharge ignition system of claim I wherein said means is an inductance element connected in series between said control switching means and the primary winding ofthe ignition coil.

3. The capacitor discharge ignition system of claim 1 wherein said means is an inductance element connected in series with said control-switching means and the primary winding of the ignition coil, said inductance element having an inductance value such that when added to the inductance value of the primary winding ignition coil as provided during the spark discharge at the secondary winding thereof provides an inductive reactance substantially equal to the capacitive reactance provided by said energy storage capacitor for a given frequency.

4. The capacitor discharge ignition system of a 1 wherein said means includes a current control device connected in circuit with the primary winding of the ignition coil, said current control device being rendered conductive upon discharge of said energy storage capacitor into the primary winding of the ignition coil to supply added current flow through the winding winding after a spark discharge ignition been established between the electrodes connected to the secondary winding of the ignition coil, said additional current flow continuing for a predetermined period of time to extend the time duration of the spark discharge between the electrodes beyond that normally obtained from a conventional capacitor discharge ignition system.

5. The capacitor discharge ignition system of claim 4 wherein said current control device is a silicon-controlled rectifier which is rendered conductive in response to the discharge of said energy storage capacitor.

6. The capacitor discharge ignition system of claim 5 wherein said silicon-controlled rectifier has its gate electrode connected to its anode by a resistance element having a resistance value to cause conduction of the silicon-controlled rectifier at a preselected point in time at which said energy storage capacitor is substantially discharged.

7. The capacitor discharge ignition system of claim 1 wherein said energy supply circuit includes a single swingblocking oscillator having a step-up transformer, the primary winding of said step-up transformer being connected to a power transistor which is rendered conductive upon sensing the discharge of said energy storage capacitor to apply a subsequent pulse of energy to said energy storage capacitor, and said means includes a silicon-controlled rectifier connected between said power transitor and the primary winding of the ignition coil to apply additional current through the primary winding substantially immediately following the discharge of said energy storage capacitor and during an established spark discharge between the electrodes connected to the secondary winding of the ignition coil, said additional current flow causing an increase in the spark duration between the electrodes.

Claims (7)

1. A capacitor discharge ignition system for generating sparkproducing potentials at the primary winding of an ignition coil so that a spark discharge is produced between electrodes connected to the secondary winding thereof, comprising: an energy storage capacitor for receiving and storing a highvoltage electrical energy pulse; an energy supply circuit coupled to said energy storage capacitor for delivering thereto a high-voltage electrical energy pulse substantially immediately after a previous energy pulse has been discharged therefrom and applied to the primary winding of the ignition coil; control-switching means connected to said energy storage capacitor and arranged for connection to the primary winding of the ignition coil; external pulse signal information means coupled to said controlswitching means to render the same conductive in response thereto substantially instantaneously to discharge said energy storage capacitor into the primary winding of the ignition coil within a relatively short predetermined time interval to initiate a spark discharge between the electrode connected to the secondary winding; and means connected in circuit with said control-switching means and arranged for connection to the primary winding of the ignition coil, said means being substantially immediately responsive to the discharge of said energy storage capacitor to extend the duration of current flow through the primary winding of the ignition coil beyond that of said relatively short predetermined time interval to increase the duration of the spark discharge produced between the electrodes connected to the secondary winding thereof.

2. The capacitor discharge ignition system of claim 1 wherein said means is an inductance element connected in series between said control switching means and the primary winding of the ignition coil.

3. The capacitor discharge ignition system of claim 1 wherein said means is an inductance element connected in series with said control-switching means and the primary winding of the ignition coil, said inductance element having an inductance value such that when added to the inductance value of the primary winding ignition coil as provided during the spark discharge at the secondary winding thereof provides an inductive reactance substantially equal to the capacitive reactance provided by said energy storage capacitor for a given frequency.

4. The capacitor discharge ignition system of a 1 wherein said means includes a current control device connected in circuit with the primary winding of the ignition coil, said current control device being rendered conductive upon discharge of said energy storage capacitor into the primary winding of the ignition coil to supply added current flow through the winding winding after a spark discharge ignition been established between the electrodes connected to the secondary winding of the ignition coil, said additional current flow continuing for a predetermined period of time to extend the time duration of the spark discharge between the electrodes beyond that normally obtained from a conventional capacitor discharge ignition system.

5. The capacitor discharge ignition system of claim 4 wherein said current control device is a silicon-controlled rectifier which is rendered conduCtive in response to the discharge of said energy storage capacitor.

6. The capacitor discharge ignition system of claim 5 wherein said silicon-controlled rectifier has its gate electrode connected to its anode by a resistance element having a resistance value to cause conduction of the silicon-controlled rectifier at a preselected point in time at which said energy storage capacitor is substantially discharged.

7. The capacitor discharge ignition system of claim 1 wherein said energy supply circuit includes a single swing-blocking oscillator having a step-up transformer, the primary winding of said step-up transformer being connected to a power transistor which is rendered conductive upon sensing the discharge of said energy storage capacitor to apply a subsequent pulse of energy to said energy storage capacitor, and said means includes a silicon-controlled rectifier connected between said power transitor and the primary winding of the ignition coil to apply additional current through the primary winding substantially immediately following the discharge of said energy storage capacitor and during an established spark discharge between the electrodes connected to the secondary winding of the ignition coil, said additional current flow causing an increase in the spark duration between the electrodes.

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