US3654910A

US3654910A - Capacitor discharge ignition circuit

Info

Publication number: US3654910A
Application number: US62398A
Authority: US
Inventors: Andrew Kuehn
Original assignee: SYSTEMMATICS Inc
Current assignee: SYSTEMMATICS Inc
Priority date: 1970-08-10
Filing date: 1970-08-10
Publication date: 1972-04-11
Anticipated expiration: 1989-04-11
Also published as: DE2131762C3; CA928775A; DE2131762B2; DE2131762A1

Abstract

A capacitor discharge ignition circuit for an internal combustion engine, the active components of which are substantially entirely solid state devices. An energy generation circuit is provided which includes a re-generative pulse amplifier and saturable transformer to convert the normal battery potential to a higher voltage. A capacitive energy storage circuit is coupled to the energy generation circuit and a triggerable switching device permits the stored energy to be discharged through the primary winding of the ignition coil. A triggering circuit which preferably has variable timing properties is coupled to the ignition breaker points and is used to time the triggering of the switching device.

Description

United States Patent I Kuehn, IH [451 Apr. 11, 1972 541 CAPACITOR DISCHARGE IGNITION 3,564,581 2/1971 Winterbum ..123/14s1z CIRCUIT 3,534,719 10/1970 Minks ..123/14s E [72] Inventor: Andrew Kuehn, Ill, St. Paul, Minn. Primary Examiner Laurence M. Goodridge [73] Assignee: Systemmatics, Inc., St. Paul, Minn. Attorney-Burd, Braddock & Bartz [22] Filed: Aug. 10, I970 [57] ABSTRACT [211 App, 62398 A capacitor discharge ignition circuit for an internal combustion engine, the active components of which are substan- [52] U.S. Cl ..123/l48 E, 315/209 tially entirely solid state devices. An energy generation circuit [51] Int. Cl ..F02p 3/06 is rovided which includes a re-generative pulse amplifier and Field 01 Search 5 1 213 saturable transformer to convert the normal battery potential to a higher voltage. A capacitive energy storage circuit is cou- [561 References Cmd pled to the energy generation circuit and a triggerable UNITED STATES PATENTS switching device permits the storedenergy to be discharged through the primary wmdmg of the 1gn1t1on c011. A trrggermg 3,312,860 1 967 S u ..3 15/209 X circuit which preferably has variable timing properties is cou- 3,413,988 12/1963 LFWIS 61 1 23/148 E pled to the ignition breaker points and is used to time the trig- 3 1 FlSheI' ..3 1 ge ing of the witching device. 3,487,822 l/l970 l-lufton et al. ....l23/148 E 3,500,808 3/1970 llinski ..l23/ 148 E 9 Claims, 3 Drawing Figures IO l2 l4 L 1 F I is l l 1.54 32 so A, 52 54 se| az l I as 60 I I 1 1 64 55 1 so I 1 68 76 I I 1 70 I I 84 l ee 74 I 94 l 1 3 1 L'Z 3 92 1- 4 102 l 96 PATENTEDAPR 1 1 |972 SHEET 1 [1F 2 INVENTOR ANDREW KUEH/V, m

BY M W 15%;

Fig.

ATTORNEYS PATENTEDAFR 1 I I972 3, 654, 91 U I I06 I20 I22 I24 KEY c M k 4 9 TO SCR SWITCH as INVENTOR ANDREW KUEH/V, ZZT

ATTORNEYS CAPACITOR DISCHARGE IGNITION CIRCUIT BACKGROUND OF THE INVENTION This invention relates generally to an ignition control circuit for an internal combustion engine and more specifically to a solid state capacitor discharge ignition unit which functions to generate an intermediate voltage during one ignition firing cycle of the system which is then discharged through the ignition coil during the next succeeding ignition firing cycle. The intermediate voltage is at a potential substantially higher than the engines battery potential, but is also substantially less than the voltage developed across the secondary winding of the ignition coil. This intermediate voltage is of a magnitude to give sufficient firing voltage to the engine spark plugs by direct transformation of voltage levels by the ignition coil such that the coil acts essentially as a pulse transformer rather than as an inductor with transformation.

The system offers the advantage of maintaining a substantially constant transfer of energy for varying states of battery charge. Further, the use of a transistorized triggering circuit for the semiconductor switch used to discharge the stored energy through the ignition coil, provides a more positively shaped pulse for triggering, with this in turn providing a high ignition voltage to be available during cranking. Also, by providing a variable timing control for the triggering circuit, a special retard function is obtained that is adjustable to fit specific engine requirements.

These and other objects and advantages will become apparent to those skilled in the art upon reading the following detailed description of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a preferred embodiment of the capacitor discharge ignition circuit of the present inventron;

FIG. 2 is a variable time delay circuit suitable for use in the triggering network of FIG. 1; and

FIG. 3 is an alternative arrangement for the variable time delay circuit of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 in which is shown a schematic diagram of the capacitor discharge ignition circuit, this circuit comprising an energy generation circuit shown enclosed by dashed line 10, an energy storage circuit enclosed by dashed line 12, a discharge circuit shown enclosed by dashed line 14, and a triggering circuit shown enclosed by dashed line 16.

Referring first to the energy generation circuit 10, this portion of the system comprises a transformer indicated generally by numeral 18 and a transistor amplifier indicated generally by numeral 20. The transformer 18 includes a saturable core 22 on which is wound a primary winding 24, a secondary winding 26 and a feedback winding 28. Primary winding 24 has a first terminal 30 connected by a conductor 32 to a terminal 34. The second terminal 36 of primary winding 24 is connected through a semiconductor diode 38 to the emitter electrode 40 of transistor amplifier 20. The collector electrode 42 of transistor 20 is connected to a point of fixed potential (ground). One terminal of the feedback winding 28 is also connected to the tenninal 36 with the other terminal 44 of feedback winding 28 being connected through a resistor 46 to the base electrode 48 of transistor amplifier 20. The terminal 34 is adapted to be connected to the positive terminal of the direct current storage battery normally associated with the engine. The negative .terminal of the battery is connected to ground.

The secondary winding 26 of transformer 18 has a first terminal 50 connected by a conductor 52 to

first terminals

54 and 56 of a pair of

condensers

58 and 60. The

condensers

58 and 60 comprise the significant portion of the energy storage circuit 12. The other terminal 62 of secondary winding 26 is coupled by means of a parallel circuit including a resistor 64 minal 68 forming a junction. The cathode electrode of diode 66 is connected to terminal or junction 68 by conductor 70. A parallel circuit including resistor 72 and diode 74 is disposed between the junction 68 and the other terminal 76 of condenser 60, tenninal 76 also forming a junction.

The energy discharge circuit 14 includes the load 78 which in this instance comprises the primary winding of the induction coil of the ignition system, with resistor 80 being connected in parallel with the primary winding 78. The parallel combination of resistor 80 and primary winding 78 is connected by a conductor 82 to the junction 56 and to ground by a conductor 84. Further included in the discharge circuit is a silicon controlled rectifier (SCR) indicated generally by numeral 86 having an anode electrode 88, a cathode electrode 90 and a trigger electrode 92. The anode 88 is connected by a conductor 94 to the junction 76. The cathode electrode 90 is coupled through diode 96 to a grounded terminal 98. Terminal 98 is also coupled through diode 100 to the junction 76. Further, a resistor 102 connects the trigger electrode 92 of the silicon controlled rectifier 86 to the grounded terminal 98.

Included in the triggering circuit shown enclosed by dashed line 16 is a semiconductor switching device indicated generally by numeral 104, a capacitor 106, the ignition system breaker points 108 with the conventional capacitor 109, optionally utilized, as well as other components interconnecting these principal components of the triggering circuit.

More specifically, the semiconductor switching device 104 (here shown as a NPN transistor) has a pair of

output electrodes

110 and 112 and a control electrode 114. The

output electrodes

110 and 112 are connected in series with the capacitor 106 between a grounded terminal 116 and the cathode electrode 90 of the silicon controlled rectifier switching device 86. A key switch terminal 118 is adapted to be connected to a source of positive potential which may be the positive terminal of the engines storage battery. Terminal 118 is coupled through a resistor 120 and a diode 122 to a junction 124 between the collector electrode 110 of semiconductor switching device 104 and a terminal of the capacitor 106. The key switch terminal 118 is also coupled through a resistor 126 to the ungrounded terminal 128 of the breaker points 108. This ungrounded terminal 128 is also coupled to a junction 130 formed between first terminals of a resistor 132, the anode of diode 134 and the cathode of diode 136. The other terminal of resistor 132 is coupled through a capacitor 138 by a conductor 140 to the junction 76. A capacitor 142 is coupled across the other terminals of the

diodes

134 and 136, the cathode and anode respectively. A resistor 144 couples the junction between the resistor I32 and the diode 134 to the base or control electrode 114 of the semiconductor switching device 104. A resistor 146 is connected between the control electrode 114 and the grounded terminal 116 of the semiconductor switching device 104.

The onoff control circuit of the system, shown by dashed line 17 includes a first transistor amplifier 148, a second transistor amplifier 150 and the

coupling resistors

152, 154 and 156. The resistor 152 couples the collector electrode of transistor amplifier 148 to the junction 158 formed between the anode of diode 134 and a terminal of resistor 144. Coupling resistor 154 connects the emitter electrode of transistor amplifier 150 to a ground terminal 160. Ground terminal 160 is coupled through a diode 162 to the key switch terminal 118. Finally, the coupling resistor 156 connects the collector electrode of transistor 150 to the base electrode of transistor amplifier 148. The emitter electrode of transistor 148 is coupled to the positive terminal of the battery by means of conductor 164.

The junction 36 between the primary winding 24 and the feedback winding 28 of transformer 18 is coupled through a capacitor 37 to a junction point 39 to which is connected a first terminal of a resistor 41 and the anode electrode of a diode 43. The cathode of diode 43 is connected to the juncand a diode 66 to the other terminal 68 of condenser 58, ter- 75 tion 76.

Now that the details of the circuit components and interconnections thereof have been set forth in detail, consideration will be given to the mode of operation of the preferred embodiment of the present invention.

operation FIG. 1

The general purpose of this system is to generate an intermediate voltage during one firing cycle of the engines ignition system that is discharged during the next firing cycle through the ignition coil. The intermediate voltage is of a magnitude to give sufficient firing voltage through the spark plugs of the engine due to direct transformation of voltage levels by the ignition coil. With this arrangement, the coil then becomes a pulse transformer instead of being an inductor with transformation as it is in prior art systems.

Initially, it is to be assumed that the positive terminal of the battery used with the system is connected to the terminal 34 while the negative terminal of the battery is connected to ground. The energy generation circuit functions to convert battery power to an intermediate voltage which is at a higher level than that of the battery. This higher intermediate voltage is stored in the energy storage circuit 12 for later discharge through the ignition coil 78. The energy generation circuit includes the transformer 18 and the semiconductor amplifier 20.

When the key switch 118 is turned on, current flows through resistor 41 and diode 43 to charge the capacitor 60 in the manner indicated by the polarity markings adjacent to it. When capacitor 60 is discharged through the discharge circuit 14, in a manner to be described hereinbelow, a current pulse is drawn through the capacitor 37 from the battery terminal 34 through the primary winding 24 through the capacitor 37 and the diode 43, through conductor 94 and the silicon control rectifier 86 and diode 96 to ground. The flow of current through the primary winding produced by this pulse induces a voltage in the feedback winding 28 of transformer 18 and this feedback voltage is of a polarity (see polarity markings on the transformer) to render the transistor amplifier 20 more heavily conducting. This lowers the impedance of the amplifier 20 thereby permitting a greater current flow through the conductor 32, the primary winding 24, the diode 38 and the emitter to collector path of the transistor amplifier 20. Thus, it can be seen that the feedback winding and the transistor act in a regenerative fashion to produce rapid saturation of the saturable core transformer 18. The flow of current through the primary winding 24 and the transistor amplifier 20 continues until the transformer core is near saturation at which time the feedback current produced by the feedback winding 28 is markedly decreased. The transistor then cuts off and current ceases to flow through the primary winding 24.

During this period of re-generative action prior to transformer saturation, very little current flows in the secondary winding 26. As soon as the current through the primary winding 24 cuts off due to saturation, the energy stored in the primary inductance is transformed to the secondary winding 26, first flowing through diode 66 and conductor 70 to charge capacitor 58. When the charge on capacitor 58 equals the' residual charge on capacitor 60, the current flowing through the secondary winding 26 flows through diode 66, diode 74 to charge

capacitors

60 and 58. The resistor 64 connected in parallel with the diode 66 serves as a bleed resistor for capacitor 58 to allow this capacitor to charge in the direction of induced voltage during primary winding current flow. This allows the secondary current to flow in the direction of diode polarity immediately upon turn-off of the current flow through the primary winding occasioned by transformer saturation. The action of the bleed resistor 64 then reduces the turn-off voltage reflected to the primary winding and applied across the emitter to collector junction of transistor 20 to an acceptable level, thereby preventing voltage breakdown of the transistor.

Transistor 20 is preferably low voltage, high conduction transistor, such as a high current germanium unit. By using diode 38 in series with the emitter-base circuit of transistor 20, any transistor leakage at elevated temperatures acts as a reverse bias further restraining the leakage flow. The diode 38 also serves the function of providing a fixed voltage off-set in the feedback circuit to thereby minimize the chance of the inductance of the primary winding resonating with circuit capacity to produce self-oscillations.

The above cycle of operation repeats itself for each firing of the silicon controlled rectifier (SCR) 86, thus re-charging the capacitor 60 to the desired potential after each firing event.

The resistor 72 serves to bleed off the charge on capacitor 60 when the system is shut down.

The resistor connected in parallel with the primary winding of the induction coil 78 is a protecting resistor which provides a discharge path for the

capacitors

58 and 60 in the event the primary winding 78 is opened or disconnected. The value of resistor 80 is selected so as to permit the SCR 86 to remain in conduction for a maximum period with minimum reduction of coil output so that the energy generation circuit will not be triggered while there is a significant voltage charge on

capacitors

58 and 60. With a limited charge on the capacitors, the turn-off voltage on the primary winding of transformer 18 will be minimized at the termination of the regeneration cycle to thereby prevent voltage breakdown of transistor 20.

The trigger and discharge circuit enclosed by dashed line 14 serves to dump the charge stored in the

capacitors

58 and 60 through the primary winding 78 of the ignition coil whenever the SCR 86 is triggered into conduction. Specifically, when SCR 86 is switched on so as to present a low impedance the charge on capacitor 60 flows to the junction 76, through conductor 94 and from the anode 88 to cathode 90 electrodes of SCR 86, through diode 96 and conductor 84, through the primary winding 78 of the coil and a conductor 82 to the other terminal 56 of the capacitor 60. By using diode 96 poled as illustrated in the cathode to ground circuit, a negative pulse can be used to trigger the SCR into conduction.

The SCR 86 is turned on when a negative pulse from the capacitor 106 in the triggering circuit 16 is applied to the cathode electrode of the SCR. More specifically, when a negative pulse is applied to the cathode 90 of SCR 86, a current flows from ground 98 through the resistor 102 connected to the gate electrode 92 of the SCR. As mentioned above, this turns the SCR on and permits the substantially larger discharge current from the capacitor 60 to flow therethrough and through the primary winding 78 of the ignition coil.

Because the ignition coil is inductive in nature, the current flow cannot cease immediately upon the discharge of

capacitors

58 and 60. Current continues to flow until a peak reverse voltage appears on

capacitors

58 and 60. At this point, capacitor 60 only reverses the direction of current flow through the ignition coil and through the diode until it is charged in a forward direction to a voltage which is a function of the unused energy recovered from this cycle of oscillation. During the reverse flow, SCR 86 is rendered non-conductive and, since the pulse has been removed from its gate electrode 92, SCR 86 clamps off and traps the residual charge on the capacitor 60. Capacitor 58, however, remains reverse charged to aid in removing voltage transients from the energy generation circuit 10. Resistor 132 and capacitor 138 tend to reduce the re-application of potential to SCR 86 for triggering purposes.

To provide reliable triggering of the SCR 86 under all operating conditions, a negative pulse triggering circuit 16 was provided. As is illustrated, the triggering circuit consists of resistor 120, diode 122, capacitor 106, resistor 102, diode 96 and semiconductor switch 104 which creates a principal firing pulse while resistor 126, the breaker points 108, diode 134, diode 136, resistor 144, resistor 146, and capacitor 142 control the conduction state of the semiconducting switching device 104.

When the key switch and diode is turned on, current also flows through

resistor

120 and 122, through capacitor 106 and diode 96 to charge the capacitor 106 when the breaker points 108 are closed. When the points open, current flows from the key switch 118 through resistor 126, through diode 134 charging capacitor 142. Current also flows through the resistor 144 and through the base 114 to emitter 112 circuit portion of transistor 104 which is connected in parallel with the resistor 146. The various component values are chosen to give a conduction rise rate for the base circuit of transistor 104 that insures a fast flow of current from ground through resistor 102, the gate to cathode junction of SCR 86, through capacitor 106 and transistor 104 to ground. Once the capacitor 106 is discharged, the collector electrode 110 of transistor 104 remains at essentially ground potential to prevent variations in the key switch voltage from re-triggering SCR 86 while the points 108 are open.

When the points 108 reclose, the charge on capacitor 142 maintains conduction in the base circuit of transistor 104 for a predetermined limited period to allow the points to come to rest, thereby obviating problems which may otherwise be caused by contact bounce. After this predetermined period has lapsed, conduction of current through transistor 104 ceases, and diode 134 blocks any back-flow of current to the points. When the transistor 104 is cut off, capacitor 106 again recharges in the manner previously described through resistor 120 and diode 122. The diode 122 provides a blocking action that allows capacitor 106 to take on the highest voltage applied to this circuit during the period in which the points 108 are closed. This offers an advantage in cold weather, especially during engine cranking when the battery voltage just before firing is at its lowest point.

The diode 136 serves as a by-pass for high potential signals that may be reflected back from the distributor during periods of high spark potential requirements. It protects diode 134 from voltage breakdown.

On some motor vehicles, a residual voltage may be fed back to the ignition circuit when the engine is running. This may be attributed to the voltage comparator circuit associated with the charge indicator light on the instrument panel which serves to indicate that the engines generating system is in a charging mode. It has been found that this voltage may be at a sufficiently high level to provide sufficient charging current in capacitor 106 to continue firing the SCR 86. To obviate this problem, the on-off control circuit 17 is provided. Circuit 17 comprises a voltage comparator circuit which senses when the key switch voltage drops below a predetermined reference level as compared to the battery voltage. When this happens, current flows continuously to the base of transistor 104 and prevents the capacitor 106 from re-charging, thus turning off the system.

With the key switch on, current flows through the base to emitter junction of transistor amplifier 150 thereby placing it in a conductive state. Since there is no resistor in the base circuit of the transistor, the voltage across resistor 154 is essentially equal to the battery voltage. Resistor 151 serves to stabilize the off" condition of transistor 150 when the key switch 118 is open and diode 162 provides a by-pass of any induction transient signals which may be occasioned by the opening of the key switch to prevent damage to transistor 150.

When the key switch voltage drops significantly below the battery voltage, current will flow from the battery terminal 34 through the emitter to base junction of transistor amplifier 148, through resistor 156, through the collector to emitter path of transistor 150 and through resistor 154 to the ground terminal 160. This provides current flow through the emitter to collector path of transistor 148 through the resistor 152 and through resistor 144 to the base circuit of transistor 104. This flow is continuous under the assumed condition and prevents capacitor 106 from charging hence the normal charging current for capacitor 106 which normally flows through resistor 120 and diode 122 is shunted to ground through the collector to emitter path of transistor 104. If the key switch voltage is zero, no current can flow to capacitor 106 from the key switch, thus

transistors

148 and 150 need only function between predetermined key switch voltage levels below battery voltage to a level which is insufficient to trigger the SCR 86 into conduction.

It is to be noted that by connecting the circuit from battery terminal 34 to the junction 158 which is common to capacitor 142 and resistor 144, that capacitor 142 serves as a filter for any short duration transient pulses introduced into the key switch circuit that might cause transistor 148 to conduct when the engine is running and the points are closed.

TIMING MODIFICATION CIRCUITS FIG. 2

In some applications it may prove desirable to provide a means for controlling the time in the cycle at which the SCR 86 is fired, thus providing for spark advance and retard" in the timing of the engine firing. FIG. 2 shows the manner in which a modest number of components may be added to the system of FIG. 1 in order to provide this feature. In FIG. 2, those components which are identical to those shown in FIG. 1 are given the same identifying numerals as were used in FIG. 1.

The timing delay circuits shown in FIG. 2, when employed, will retard the spark timing over a specified low RPM range of the engine and effectively will cut off above the given RPM range.

In FIG. 2, the transistor 166 is added in the base circuit of transistor 104. Specifically, the emitter to collector path of the transistor 166 is connected in series between the resistor 144 and the base junction 114 of transistor 104. The base electrode of transistor 166 is connected by means of a conductor 168 to a junction 170 to which is connected a first terminal of a resistor 172 and a resistor 174. The other terminal of resistor 172 is connected to ground. The other terminal of resistor 174 is connected to the emitter terminal of a transistor 176. The base electrode of transistor 176 is connected through a resistor 178 to the junction 130. The collector electrode of transistor 176 is coupled through a variable resistor 180 to the key switch terminal. Finally, a capacitor 182 couples the collector electrode of transistor 176 to the junction 130.

Transistor 166 will not conduct upon the opening of points 108 until such time that the voltage across resistor 172 is low enough to provide a sufficient flow of current from the points 108 through diode 134, through resistor 144, through the emitter to base junction of transistor 166 through resistor 172 to ground. Current flow through the emitter to base path of transistor 166 lowers the impedance presented in the emitter to collector path of the transistor 166 such that base current for the transistor 104 is provided. With base current provided to the transistor 104, it conducts and operates in the manner described in connection with FIG. 1 to effect a firing of the SCR 86.

Delay in the conduction of transistor 166 is caused by a charge on the capacitor 182 flowing through transistor 176 and the

resistors

174 and 172 when the points 108 are near battery voltage (points open). Resistor 178 causes transistor 176 to be conductive when the points 108 are opened but nonconductive when the points are closed.

When the points 108 are closed, the junction of capacitor 182 and resistor 178 will be at ground potential and capacitor 182 will charge at a rate determined by the RC time constant of resistor 180 and capacitor 182. Provided the charge on capacitor 182 is sufficient to cause the voltage across resistor 172 to exceed the junction voltage of transistor 166, transistor 166 will be held non-conducting until such time that capacitor 182 is nearly discharged. Capacitor 182 continues to provide current until it is reverse charged. With this reverse charge, if the dwell period is insufficient to give a forward charge on capacitor 182, no delay will take place on the triggering of the transistor 104. Resistor 174 is a stabilizing and restricting resistor to control the flow of charge from the capacitor 182 to ground.

The delay provided by the circuit of FIG. 2 is useful during starting and low RPM conditions to create a retard that prevents pre-ignition during cranking and exhaust emission control during idle. The circuit can be adjusted so as to be inoperative at any desired RPM value so as to allow the normal timing controls to be effective during acceleration and power pulling use of the engine.

One factor in the calibration of the circuit of FIG. 2 is the dwell period, i.e., the period that the breaker points are closed between firings expressed in degrees of distributor rotation or percentage of period between firing. The embodiment of FIG. 3 shows a similar circuit for controlling the timing of the firing of the SCR 86, but one in which the dwell period is no longer a factor of calibration. Again, in FIG. 3, those components which have already been described in connection with FIGS. 1 and 2 have the same numerical identifiers as used in those Figures.

The circuit of FIG. 3 is quite similar to that of FIG. 2 except for the addition of an additional pair of

transistor amplifiers

184 and 186.

Transistors

184 and 186 can be one multiple junction device or in the alternative, two two-junction devices. The emitter electrode of transistor 184 is connected to the junction 130 and the base electrode is connected through a resistor 188 to this same junction. The collector electrode of transistor 184 is connected to the base electrode of transistor 186 and through a resistor 190 to ground. The collector of transistor 186 is connected to the base electrode of transistor 184. A resistor 192 couples the emitter electrode of transistor 186 to its base electrode and the emitter electrode of transistor 186 is connected to a first terminal of the timing capacitor 182.

Besides being connected to the base electrode of the transistor 184, the collector electrode of transistor 186 is coupled through a resistor 194 and a capacitor 196 to ground.

As was mentioned above, the circuit of FIG. 3 is very similar to that of FIG. 2, but with the addition of the

transistors

184 and 186 to allow the capacitor 182 to begin re-charging as soon as it has initially discharged due to the opening of the points. When the points open, current from the point circuit flows through the emitter to base junction of transistor 184 through resistor 194 and capacitor 196 to ground. This causes transistor 184 to conduct through its collector to the base of transistor 186, through the base to emitter path of transistor 186 and through the capacitor 182, a diode 198, the collector to emitter path of transistor 176 and

resistors

172 and 174 to ground. The effect on the discharge of capacitor 182 is as described before. The collector circuit of transistor 186 maintains the current flow through transistor 184. As soon as capacitor 182 is discharged, thereby allowing transistor 166 to conduct and fire the circuit, current continues to flow through capacitor 182 until charged in a reverse direction. When capacitor 182 is reverse charged,

transistors

186 and 184 turn off and the capacitor 182 begins to discharge because of the current from the key switch through resistor 180, capacitor 182, resistor 192 and 190 to ground. If the charge rate is sufficient to put a forward charge on capacitor 182, then it will cause the retard effect to occur when the points open on the next firing cycle. If the charge rate is not sufficient to place a forward charge on capacitor 182, then the circuit has no effect on the timing. As the re-charge of capacitor 182 in the forward direction starts as soon as it is discharged, the dwell period has no effect on the retard period. Diode 198 prevents capacitor 182 from immediately discharging its reverse charge through the resistors 192 and 190, and the base to collector junction of transistor 176.

While the circuit forming the preferred embodiment of this invention whereby transistorized control of the SCR triggering circuit is employed, gives a more positive shaped pulse for triggering, and has the advantage of locking in the highest available voltage during cranking. Also, it allows one to continue using the conventional capacitor across the breaker points in the ignition system, making the system easily converted from a discharge ignition to conventional ignition for servicing the system. Furthermore, by providing a fixed delay in restoring the charge on the capacitor 106, the effect of contact bounce is eliminated instead of merely being filtered out. I-Ience, double firing of the SCR is avoided. Finally, the timing modification circuits of FIGS. 2 and 3 can provide a special retard function that can be made adjustable to fit specific engine requirements.

While there has been described and illustrated a preferred embodiment of this invention, it will become apparent to those skilled in the art that various modifications and changes can be made. For example, if a positive ground system is desired, it is advantageous to discharge the capacitor 60 through a gated semiconductor switch (SCR 86) to ground then through the primary winding of the induction coil. In this way, any moisture or leakage path to ground on the primary winding of the induction coil would not cause capacitor 60 to be discharged between firings. For a positive ground system,it is only necessary that the polarities of all semiconductors be reversed and that the battery polarity be reversed. The SCR device in the form of a triac or other bi-polar device which may be utilized, may still be triggered either negatively or positively using principles set forth in the foregoing specification. Accordingly, the invention described herein should only be limited in accordance with the scope of the appended claims.

I claim:

1. In an ignition control circuit for an internal combustion engine comprising, in combination:

a. a voltage generating circuit adapted to be connected to a source of direct current at a first potential for generating at an output voltage of a substantially higher potential;

b. energy storage means coupled to said output of said voltage generating means for at least temporarily storing an electrical charge;

c. means including triggerable switching means adapted to couple said energy storage means in series with the primary winding of an induction coil; and

d. triggering means responsive to the opening and closing of ignition breaker points for applying triggering signals to said triggerable switching means such that when said triggerable switching means receives a triggering signal, the charge in said energy storage means is caused to flow through said primary winding for a predetermined time period, the improvement comprising:

1. said voltage generating circuit including a saturable transformer means having primary and secondary windings with means directly coupling said primary winding to said source of direct current potential; and

2. said triggering means comprising a semiconductor switching means having a pair of'output electrodes and a control electrode, a capacitor connected in series with said pair of output electrodes and a control electrode, a capacitor connected in series with said pair of output electrodes and said triggerable SWITCHING means; means connecting said control electrode to said ignition breaker points; means for charging said capacitor to a predetermined voltage when said breaker points are closed and for rendering said semiconductor switching means conductive when said points are open.

2. Apparatus as in claim 1 wherein said saturable transformer comprises a primary winding, a secondary winding and a feedback winding; semiconductor current controlling means having first, second and control electrodes; means connecting said first and second electrodes in series circuit with said primary winding and across a source of direct current; means connecting said feedback winding to said control electrode, such that when a current pulse flows through said primary winding, a voltage is induced in said feedback winding to enable additional current to flow through said primary winding and said semiconductor current controlling means in a regenerative manner to induce a voltage of a high potential across said secondary winding.

3. Apparatus as in claim 2 wherein said energy storage means is operatively coupled to said secondary winding.

4. Apparatus as in claim 3 wherein said energy storage means comprises at least one capacitor having first and second terminals; means connecting one of said terminals to one terminal of said secondary winding and a unidirectional current conducting device coupling said second terminal to the other terminal of said secondary winding.

5. Apparatus as in claim 1 wherein said triggerable switching means comprises a silicon controlled rectifier having a first and a second electrode and a trigger electrode, said first and second electrodes being connected in series circuit with said primary winding of said induction coil and said energy storage means.

6. Apparatus as in claim 5 and further including means for coupling said trigger electrode to said triggering means.

7. Apparatus as in claim 1 wherein said triggerable switching means comprises a triac having a pair of output electrodes connected in series circuit with said primary winding of said induction coil and said energy storage means.

8. Apparatus as in claim 7 wherein said trigger electrode is coupled to said triggering means.

9. Apparatus as in claim 1 wherein said means connecting said control electrode to said ignition breaker points includes a time delay network to maintain said semiconductor switching means non-conductive for a predetermined period following the opening of said ignition breaker points.

3 33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N 3 ,654 ,910 Dated April 11 1972 lnventofls) Andrew Kuehn III It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 1, after "switch", -ll8 should be added and and diode" should be omitted.

Column 5, line 2, before "122", -diode should be added.

Signed and sealed this 5th day of September 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK Commissioner of Patents EDWARD M FLETCHER J R Attesting Officer

Claims

1. In an ignition control circuit for an internal combustion engine comprising, in combination: a. a voltage generating circuit adapted to be connected to a source of direct current at a first potential for generating at an output voltage of a substantially higher potential; b. energy storage means coupled to said output of said voltage generating means for at least temporarily storing an electrical charge; c. means including triggerable switching means adapted to couple said energy storage means in series with the primary winding of an induction coil; and d. triggering means responsive to the opening and closing of ignition breaker points for applying triggering signals to said triggerable switching means such that when said triggerable switching means receives a triggering signal, the charge in said energy storage means is caused to flow through said primary winding for a predetermined time period, the improvement comprising: 1. said voltage generating circuit including a saturable transformer means having primary and secondary windings with means directly coupling said primary winding to said source of direct current potential; and 2. said triggering means comprising a semiconductor switching means having a pair of output electrodes and a control electrode, a capacitor connected in series with said pair of output electrodes and a control electrode, a capacitor connected in series with said pair of output electrodes and said triggerable SWITCHING means; means connecting said control electrode to said ignition breaker points; means for charging said capacitor to a predetermined voltage when said breaker points are closed and for rendering said semiconductor switching means conductive when said points are open.

2. said triggering means comprising a semiconductor switching means having a pair of output electrodes and a control electrode, a capacitor connected in series with said pair of output electrodes and a control electrode, a capacitor connected in series with said pair of output electrodes and said triggerable SWITCHING means; means connecting said control electrode to said ignition breaker points; means for charging said capacitor to a predetermined voltage when said breaker points are closed and for rendering said semiconductor switching means conductive when said points are open.