US3741183A

US3741183A - Capacitor discharge ignition system

Info

Publication number: US3741183A
Application number: US00886972A
Authority: US
Inventors: T Sturm
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-12-22
Filing date: 1969-12-22
Publication date: 1973-06-26
Anticipated expiration: 1990-06-26

Abstract

An improved capacitor discharge ignition system for internal combustion engines, wherein the ignition system utilizes a discharge capacitor power source placed in shunt with the primary winding of a transformer which automatically turns off upon saturation thereof so that the magnetic field collapses and the secondary winding of the transformer produces a pulse current to charge the capacitor. The capacitor is subsequently placed in shunt with the primary winding of a pulse transformer so that the secondary winding thereof delivers a high voltage spark to the distributor and ultimately the spark plugs of an engine. In the ignition system of this invention the capacitor discharge sequence and the transformer charging sequence are commenced simultaneously so that a maximum number of sparks are capable of being produced in the minimum amount of time.

Description

United States Patent 1191 Sturm 1 June 26, 1973 CAPACITOR DISCHARGE IGNITION OTHER PUBLICATIONS SYSTEM P 1 El t C I 't' S t b [76] Inventor: Theodore F. Sturm, 44900 Viejo iss 8;? gm m ys y Drive, l-lemet, Calif. 92343 Filfidl 1969 Primary Examiner-Laurence M. Goodridge Assistant Examiner-Ronald B. Cox [21] Appl' 886972 Attorney-Roman A. Di Meo [52] US. Cl 123/148 E 51 Int. Cl. F02p 1/00 [57] ABSTRACT [58] Field of Search 123/148 C An improved capacitor discharge ignition system for internal combustion engines, wherein the ignition sys- [5 6] References Cited tern utilizes a discharge capacitor power source placed UNITED STATES PATENTS in shunt with the primary winding of a transformer 3 263,124 7/1966 Stuermer 315/212 which aummaficany off saturation them 271,593 9/1966 devilbiss 0 307/252 so that the magnetic field collapses and the secondary 3,312,860 4/1967 3mm 315/223 winding of the transformer produces a pulse current to 3,331,986 7/1967 Hardin.... 315/200 charge the capacitor. The capacitor is subsequently 3,418,988 12/1968 Lewis 123/148 placed in shunt with the primary winding of a pulse ,500, /19 l s i /148 transformer so that the secondary winding thereof de- 3'242,420 1966 f y 123/148 livers a high voltage spark to the distributor and ulti- 3399876 H1967 23/148 mately the spark plugs of an engine. In the ignition sysa gfgs tem of this invention the capacitor discharge sequence 3 383 556 5/1968 Tarter...:::::: :11: 123/148 and the .transformer charging sequence are 3:398:353 8/1968 Noddin 123,148 menced simultaneously so that a maximum number of 3,415,234 12/1968 Dammann 123/148 Sparks are capable 0f being Produced in the minimum 3,487,822 l/l970 Hufton 123/148 amount of time. 3,520,288 7/1970 Dusenberry.... 123/148 3,543,109 11/1970 Minks 123/148' 1 Clam, 8 Drawmg Flgul'es PAIENIEDauuzs I975 v 3.741.183

sum

2 or 2 INVENTOR THEOQOA A'57UPM /4 ATTQQ/VEY 1 CAPACITOR DISCHARGE IGNITION SYSTEM In typical capacitor discharge ignition systems, energy in the form of an electrical charge is stored in a capacitor (also referred to as a condenser.) Such stored energy may be maintained without appreciable loss for a considerable time without the further expenditure of energy due to the insulation properties of the dielectric between the plates of the capacitor.

When a spark is desired for igniting a fuel charge in an internal combustion engine, the capacitor is switched in shunt with a pulse transformer primary windin g while the secondary winding delivers a stepped up voltage to the point of energy use, i.e., a conventional spark plug. According to the published state of the art, a thyratron tube or a semiconductor regenerative device such as a semiconductor controlled rectifier (hereinafter referred to as SCR) is normally used to perform the switching function.

In order to accomplish the foregoing economically and without the use of special parts, the preferred voltage to which the capacitor is charged is in the several hundred volts range, i.e., 300 or 400 volts. Since the electrical power sources normally associated with internal combustion engines produce from 6 to 24 volts, a means for charging the capacitor is required.

In conventional multicylinder engines which are operable at high speeds, the time interval between demands for igniting sparks are extremely short, i.e. 2 milliseconds. Accordingly, the minimum cycling time for the ignition system, namely t, 2 must be equal to or less than the aforesaid spark demand time interval. To conserve and maximize the use of the available time, this invention utilizes a switching sequence wherein both the capacitor discharging switch (normally a SCR) and the transformer charging switch (normally a transistor) are simultaneously triggered into conduction upon a signal from the engine timing device (spark demand).

Although there are a number of methods for charging the capacitor, this invention uses a transformer in combination with a switch and diode rectifier. The switch connects the primary winding of this transformer to a source of direct current voltage, such as a conventional storage battery, which causes current in the primary to rise proportionally with time lapse (not taking into account the second order effects of ohmic resistance). The rate of rise of the current in the primary winding IS where V is the voltage of the battery or power source and L the inductance of the primary winding.

According to the invention, means are provided to open the switch when the current reaches a desired value I. At this moment an amount of energy which is stored in the primary winding will transfer through the secondary winding and the rectifier to charge the storage capacitor (having C capacitance). Such energy transfer requires a time interval which is the duration of one-quarter cycle of the natural frequency of the tuned circuit formed by the inductance of the secondary winding and the capacitor. The energy inductively stored in the transformer is, in Joules, equal to 9% L! (L is inductance and l is current). The switch is kept closed for a time interval t IL/V (l is current, L is inductance and V is voltage).

Triggering the SCR results in an oscillatory discharge of the storage capacitor through the pulse transformer and a spark at its output. The simultaneous triggering of the transistor commences the time interval t, during which energy stores in the transformer. Before the transistor is switched off (when t terminates and t commences), the SCR returns to a nonconduction state. Times are in the order of t, about 1.3 milliseconds, t about 0.6 milliseconds, and capacitor discharge (spark) time about 0.005 to 0.5 milliseconds, depending upon the characteristics of the pulse transformer. Accordingly, it is an object of this invention to provide a simple, inexpensive ignition system for internal combustion engines capable of high efficiency and increased component life.

Another object is to provide a simple, inexpensive capacitor discharge ignition system which produces higher spark rates than heretofore obtained yet producing less heat and electrical loss in the system.

A further object is to provide a simple, inexpensive capacitor discharge ignition system which requires less time between firings and which requires less power for a given firing speed.

Still another object is to provide a simple, inexpensive capacitor discharge ignition system which can be utilized with higher engine speeds.

Yet another object is to provide a simple, inexpensive capacitor discharge ignition system which includes a charging circuit and a discharge circuit for discharging energy into a spark producing circuit, wherein the charging circuit and the discharge circuit are simultaneously activated by a command signal in synchronism with the internal combustion engine.

Another object is to provide a simple, inexpensive capacitor discharge ignition system, wherein the charging circuit and the discharging circuit are activated without the use of added means to generate a command signal to the charging circuit.

Still another object is to provide a simple, inexpensive capacitor discharge ignition system having substantially constant firing spark energy over a large environmental temperature range and which is insensitive to voltage fluctuations of the source voltage.

Yet another object is to provide a simple, inexpensive capacitor discharge ignition system which cannot be falsely triggered by voltage transients from the source voltage.

Another object is to provide a simple, inexpensive capacitor discharge ignition system which permits retrofitting to the internal combustion engine without removing the capacitor which normally shunts the contact points.

Still another object is to provide a simple, inexpensive capacitor discharge ignition system which prevents the return of the capacitor energy in the charging circuit to the voltage source.

Yet another object is to provide a simple, inexpensive capacitor discharge ignition system which produces a signal that indicates the speed of the internal combustion engine.

Another object is to provide a simple, inexpensive capacitor discharge ignition system which can be activated by command signals from synchronous magnetic, contact, capacitive or optical means.

Other objects and advantages will be readily apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an ignition system utilizing the elements of the invention herein and which also provides for an extremely economical tachometer;

FIG. 2 is a set of curves illustrating the time relationships during the operation of the system of FIG. 1;

FIG. 3 shown another variation of the circuit of FIG. 1;

FIG. 4 is a set of curves illustrating the waveforms and time relationships occurring during the operation of the system of FIG. 3;

FIG. 5 is a schematic diagram of an alternate circuit of the ignition system of FIG. 1;

FIG. 6 is a variation of the circuit of FIG. 5;

FIG. 7 is still another variation of the circuit shown in FIG. 1; and I FIG. 8 is another variation of the circuit of FIG. 1, except that the circuit of the SCR is replaced with a lightactivated switch circuit.

Referring more particularly to FIG. 1, a schematic diagram of a circuit is shown where the triggering action is derived from conventional cam-operated breaker points, with the cam mechanically driven in synchronism with the engine. In the circuit of FIG. 1, triggering is enabled when ignition switch 39 is closed.

The triggering circuit functions as follows. When contact 38 is closed, battery current through

resistors

36 and 35 is bypassed to ground 38g. Another portion of the current flows through resistor 40 and ground 403. A third portion of the battery current passes through the emitter and collector of transistor 41 (PNP type). This latter current then flows through

resistors

34 and 32 to positively charge plate 31a of capacitor 31 while the charge from the opposite plate 31b returns to ground 31g. There is a negative battery voltage at the anode of diode 42, keeping this diode nonconductive. Transistor 37, having no forward bias to its base, will not conduct through its collector, thereby keeping the triggering current from reaching either the gate 17 of SCR or the base 25b of transistor 25.

When capacitor 31 has accumulated a sufficient charge and contact 38 is opened, the following occurs. No battery current flows through the base of transistor 41, causing the collector of transistor 41 to stop conduction of current. This enables the current from condenser 31 to pass through the emitter and base of transistor 37, diode 43 and resistor 40 to ground 40g. Thus, transistor 37 is able to conduct a strong collector current from condenser 31 through resistor 30, diode 46 and the base and emitter of power transistor 25 to ground 25g. Part of this collector current conducted by transistor 37 passes through resistor 47 through gate 17 of SCR 15, thereby triggering said SCR 15 into conduction. The current which originated on plate 31a of condenser 31 and flowed to ground 25g is returned to plate 3lb'of condenser 31 via ground 31g.

As can be seen, capacitor 31 delivers current through three parallel paths: (1) through resistor 32, diode 43 and resistor 40 to ground 40g,- 2) through the emitter and base of transistor 37, diode 43 and resistor 40 to ground 40g (this current enables heavy conduction between the emitter and collector of transistor 37); and (3) through the collector of transistor 37, which is also split into two portions, one going via resistor 47 to the gate 17 of the SCR 15 thereby triggering it into conduction. the other simultaneously going via resistor 30 and diode 46 to the base 25!; of transistor switch 25 thereby latching it into conduction to commence time interval t Capacitor 31 is discharged in a fraction of the time interval During time interval t there exists appreciable positive voltage at the base of switch 25. The purpose of diode 46 is to keep this voltage from furnishing gate current to the SCR 15.

The capacitor discharge circuit functions as follows. When SCR 15 has been triggered, capacitor 14 is shunted to the primary winding 12 of pulse transformer 11 and to diode 48. The charge on capacitor 14 is so polarized that diode 48 will not conduct at first, but the current will build up in primary winding 12. This current has a sinusoidal waveform until one-fourth of one cycle'has elapsed. During this same time period, the voltage across capacitor 14 (and primary winding 12) follows a cosine waveform. As the capacitor voltage reaches a value of zero, the current in primary winding 12 is at the maximum and all energy has been transferred'from the capacitor into the pulse transformer. As the voltage attempts to reverse its polarity, diode 48 starts conducting and diverts the current thereby forcing SCR 15 out of conduction. The current keeps running through the primary winding 12 and decays gradually as the energy dissipates. This current actually consists of two components: (1) a magnetizing current which assumedly runs through the primary winding 12, and (2) a useful current which, in accordance with long established principles, may be assumed to run through a stray reactance to an ideal transformer which is loaded with a capacitance and the spark gap of the spark plug. Since the primary inductance is quite large compared to the stray reactance, the useful component (2) far exceeds the magnetizing current (1). Thus, the useful component (2) of the current, supported by the diode 48, results in a strong and relatively prolonged secondary current maintaining the are at the spark gap discharge. Such a discharge is quite hot and, therefore, particularly suited to providing ignition of the fuel-air mixture in an engine.

In the embodiment of FIG. 1, without capacitor 44 and resistor 45, the collector-to-base capacitance of transistor 25 would permit a positive voltage transient on the battery line to cause base current to flow in transistor 25 and thus commence a charge cycle, without providing turn-on of the SCR 15. If repeated, the energy accumulating in capacitor 14 can reach a level to destructively break down the SCR 15 resulting also in an untimely spark. The capacitor 44, however, precludes the base voltage of transistor 25 from reaching high enough levels to turn on transistor 25. Resistor 45 drains capacitor 44 so that the voltage at the base cannot be raised by any transient to a level sufficient to turn on transistor 25.

From the circuit embodiment of FIG. 1 a means for deriving accurate tachometer signals is also obtained. Since this system allows the current in primary winding 22 of transformer 21 to rise until it is cut off at a well defined and invariable level, transformer 21, when discharging, will show an invariable number of voltseconds (see time interval t, in FIGS. 2(b) and 4( b). DtTring time interval t this voltage is passed by diode 49 from lead 49a to an averaging type voltmeter consisting of resistor 50 and a measuring movement 51. Resistor 50 may be calibrated to fully deflect the meter at a desired engine speed. Thus, since all other elements already exist in the embodiment of FIG. 1, an accurate tachometer of unusual economy is provided by the addition of diode 49, resistor 50 and measuring movement 51 in the circuit arrangement disclosed.

FIGS. 2(a) and 2(b) illustrate the waveforms and time (t) relationships resulting from operation of the circuit of FIG. 1. In FIGS. 2(a) and 2(b), the action of the triggering contact 38 and the voltage at the collector 250 of transistor 25, respectively, are depicted. FIG. 2(c) illustrates the voltage at the junction of secondary winding 12 of pulse transformer 11, capacitor 14, secondary winding 24 of transformer 21 and diode 48. FIG. 2(d) shows the waveform of the voltage at the spark gap 10.

FIG. 3 illustrates another embodiment of the circuit of FIG. 1. In this embodiment the triggering circuit is modified by deleting resistors 36 and 40,

diodes

42 and 43 and transistor 41. Inserted in the circuit are resistor 52 and a NPN type transistor 33 is substituted for PNP type transistor 41.

While engine driven contact 38 is closed (prior to the demand for a spark), current through resistor 35 is bypassed to ground 38g so that transistor 33 is nonconductive. This permits current to run through

resistors

34 and 32 to charge the lower plate of capacitor 31 positively while the charge from the upper plate is enabled to return to ground 18g through diode 18.

When contact 38 is opened, current through resistor 35 runs through the base 33b of transistor 33 so that transistor 33 is able to carry a strong collector current. The collector current consists of three components: l battery current through resistor 34; (2) current from condenser 31 through resistor 32; and, (3) current from condenser 31 through emitter and base of transistor 37 and resistor 52. The last mentioned component enables transistor 37 to conduct a strong collector current from condenser 31 through resistor 30 and the base 25b to emitter junction of power transistor 25 to ground 25g. This strong collector current from condenser 31, in addition to' the current components (2) and (3) which originated on the lower plate of condenser 31 and fed to ground 25g, is returned to the upper plate of condenser 31 via ground 18g through gate 17 and cathode 16 of the SCR 15.

The current passing through the base emitter junction of transistor 25 (NPN type) enables said transistor to conduct collector current from the battery through primary winding 22 of saturable transformer'21. As a result, a voltage is induced in the feedback winding 23 so as to send current through diode 26 and resistor 27 into the base 25b of transistor 25. This action latches the transistor 25 in a conducting state even after condenser 31 has been discharged. Voltage induced in secondary winding 24 has a polarity whereby diode blocks any current flow therein.

The current in primary winding 22 will essentially increase linearly with time as long as the transformer is unsaturated, assuming sufficient current gain in the transistor 25. Upon the commencement of saturation of the transformer, the current will attempt to rise more rapidly and to a higher level. Since transistor has a limited base current and a finite current gain, the transistor will of necessity become unsaturated which means that the voltage deployed across primary winding 22 will collapse. Since this results in less base drive current being furnished, regenerative action will unlatch transistor 25 and interrupt the current flow in its collector. It should be noted that all of the foregoing sequence occurs in the time interval hereinabove referred to as t,.

When transistor 25 is triggered into conduction, the SCR 15 is also triggered. When this initially occurred and ignition switch 39 was turned on, storage capacitor 14 was not yet charged so that SCR 15 could not conduct any current out of capacitor 14. If, however, capacitor 14 is charged with its left side positive, as will be hereinafter explained, and SCR 15 is triggered on, the positive plate 14a of capacitor 14 is connected to ground 18g via SCR 15 and diode 18. Thus, its negative plate 14b is placed in shunt with primary winding 12 of pulse transformer 11.

In the closed circuit consisting of capacitor 14, SCR 15, diode l8 and primary winding 12 of pulse transformer 11, a current will commence to flow which has a sinusoidal waveform. After completion of one-half of the wave and the current waveform attempts to pass through zero, the SCR will return to its nonconducting state since the triggering pulse has already decayed. During the first quarter wave, the energy stored in the capacitor 14 is transferred into the inductance of the pulse transformer 11. A large portion of the energy is consumed in causing a spark discharge across the spark plug 10.

During the second quarter wave, any remaining energy is transferred back into capacitor 14 by charging it to the opposite polarity. By the use of optional diode 19, the energy which is again in capacitor 14 is given the opportunity to discharge over primary winding 12 even without the conduction benefit of SCR 15. This will take place during the second half of the sine wave and will permit another discharge spark across the spark plug 10.

It should be noted, however, that another action occurs while capacitor 14 has a negative charge on plate 140. This negative polarity renders diode 20 conductive and places the capacitor voltage across secondary winding 24 of the saturating transformer 21, causing the dotted end in all transformer windings to be positive. In particular, this means that the direction of current flow in primary winding 22 attempts to reverse. This reversal of the current direction is eased by the forward conduction by Zener diode 29 which is in parallel with transistor 25.

Considering again the generation of the igniting spark, it should be noted that primary winding 12 of the pulse transformer 1 1 is in shunt with the relatively large capacitance of capacitor 14 so that the current through the said primary winding would only be able to build up relatively slowly. On the other hand, according to well known principles, the reflected capacitance of the secondary winding 13 may be assumed to be connected across the winding 12 by a small inductance commonly referred to as stray reactance. This stray reactance has a value of l to 20 per cent of the primary inductance, depending upon the particular transformer design. It should further be noted that the voltage across the shunt (parasitic) capacitance of the secondary winding 13 can rise relatively quickly because of the small value of the stray reactance. While this feature is not novel with this invention, it permits a higher rate of voltage rise than most ignition systems and thereby is instrumental in firing plugs whose insulation is poor because of fouling.

The manner by which storage capacitor 14 receives its charge is as follows. At the end of time interval t,

when transistor 25 ceases to conduct, the magnetic field of transformer 21 will begin to collapse. Assuming that the transformer has no stray reactance, i.e., alllines of force that link one winding link all the other windings as well, the collapsing field will induce voltages in the windings which have negative polarity at the end where the dot is shown. This polarity renders diode 20 conductive and thereby capacitor 14 is in shunt with secondary winding 24 and becomes charged. It is at this moment that time interval t, commences. The voltage in all windings will then. be sinusoidal with the frequency determined by the resonance frequency of capacitor 14 in conjunction with theinductance of secondarywinding 24.

Time interval equals a quarter cycle at the end of which diode 20 is again nonconductive. It should be noted that during time interval t diode 26 is in reverse bias so that no energy is extracted from it. A small amount of energy is dissipated in resistor 28. The purpose of resistor 28 is to dampen oscillations of the transformer with its own parasitic winding capacitance. Such oscillations would occur at the end of time interval I, when these parasitic capacitances are charged to a high voltage. If these oscillations are inadequately dampened, any remaining energy after the quarter cycle is completed would turn on transistor 25 resulting in uncontrolled oscillations. However, as aforesaid, this is eventually prevented by resistor 28.

It should be further noted that transformer 21 cannot be economically constructed whereby it is 100 percent free of stray reactance. The energy stored in this stray reactance while primary current I still flows, will attempt to create ahigh voltage spike" at the collector of transistor 25 when it is turned off. If this were permitted, transistor 25 may be destroyed by a secondary breakdown. Diode 29 is a Zener diode which limits this spike to a harmless value. This would also be achieved if Zener diode 29 were connected to the base 25b of transistor 25 instead of to ground 29g. In this case, the bulk of the energy absorption would be performed by the transistor 25. I

FIGS. 4(a) through 4(d) which are similar to FIGS. 2(a) through 2(d) illustrate several waveforms and time (t) relationships derived as a result of the use of the instant invention hereinabove described in FIG. 3, wherein:

4(a) indicates the action of the triggering contact 38;

4(b) depicts the voltage at the collector 25c of transistor 25;

4(c) shows the voltage at the junction of secondary winding 12 of pulse transformer 11; and

4(d)' shows the voltage at the spark plug, which sparks before the voltage has an opportunity to reach its maximum (otherwise it would not spark because of insufficient'voltage or excessive spark gap width).

FIG. shows still another method of triggering the system of the instant invention. Here the power transistor 25 has PNP polarity. When the timing contact 38 is closed, battery current will flowvia resistor 53 and divide into two portions, one through diode 54, the other through primary winding 56 of the triggering transformer 55 and then to contact 38 and ground 38g. The inductance of primary winding 56 causes the current through said winding to rise relatively slowly. Voltage induced in secondary winding 57 will not cause a current to flow because both the emitter base junction of transistor 25 and the gate junction of SCR 15 are reverse biased by that voltage.

If contact 38 is now opened to obtain a spark, the collapsing magnetic field of triggering transformer 55 causes opposite polarity voltages to occur in both its primary and secondary windings. Thus, diode 54 will not conduct, whereas the emitter-base junction of transistor 25 and the gate-cathode junction of SCR 15 will conduct triggering current. Accordingly, a spark will occur which was immediately preceded by the transistor 25 latching into conduction, as was described relative to the circuit shown in FIG. 3. In all other respects the two circuits are similar.

FIG. 6 depicts a variation of the circuit shown in FIG. 5 which permits the use of a more economical NPN power transistor 25. In this variation, diode 18 used in FIG. 3, and new diode 58 which was not required in the variation of FIG. 5, are utilized here. As was hereinbefore indicated, the transistor (or other switch) is opened at the end of time interval t when the primary current in transformer 21 reaches a predetermined value I. In the circuit of FIG. 6 as well as those of FIGS. 1, 3 and 5, this current value is determined by the saturation of the transformer core.

FIG. 7 illustrates still another variation to the circuits of FIGS. 1, 3, 5 and 6. In this circuit variation the of current will be interrupted before saturation is reached. This can lead to significantly reduced iron losses (energy losses in the iron core). When the current which leaves the emitter or transistor (NPN type) 25 exceeds the cut-off limit and reaches ground through resistor 59, the .voltage drop across resistor 59 exceeds the base-emitter conduction threshold voltage of transistor 60 and causes its collector to absorb a major portion of the feedback (latch-on) current coming from resistor 27. This would absorb the base drive current which would be needed by transistor 25 to keep it in conduction. Regenerative action will therefore unlatch transistor 25 and interrupt the primary current of transformer 21 as is intended without any reliance on saturation of the transformer core.

A further variation from the previously disclosed circuits is also shown in FIG. 7. Specifically, rectifying diode 20 is replaced with the components SCR 61, diode 62, resistor 63 and capacitor 64. Although this circuit is more complicated and more expensive than those of FIGS. 1, 3, 5 and 6, it provides an important advantage. In this circuit, SCR 61 has its gate so connected that voltage of capacitor 14, regardless of polarity, cannot trigger said gate. However, when secondary winding 24 becomes negative on its dotted side and SCR 61 is not yet conducting at the beginning of time interval t,, a very high rate of voltage rise occurs because of the absence of load except for the path consisting of capacitor 64, diode 62 and gate-cathode junction of SCR 61. Therefore, despite the small value of the capacitance of capacitor 64, a very strong current will be fed to the gate of SCR 61 and very quickly trigger the SCR 61 into forward conduction.

Continuing from this moment throughout time interval SCR 61 will act exactly as did diode 20. It should be noted that this circuit assures proper charging of capacitor 14 without permitting delivery of energy from the capacitor to the transformer, thereby avoiding the problem wherein the negative voltage on capacitor 14 during a spark discharge could reach the power transformer through diode 20 and do unnecessary double triggering of 25 as well as feed energy from the capacitor discharge to the battery.

FIG. 8 depicts a suitable circuit which uses a source of light 65 (e.g. an incandescent bulb, a galliumarsenide infrared emitter or some other suitable light source), an engine driven shutter 66 which is synchronized so as to block the light unless a spark is demanded, and a light activated switch 67 (hereinafter referred to as LAS) which latches into conduction if irradiated and unlatches when current flow ceases. The LAS when compared with other light sensors has the advantage of being able to carry very appreciable current after irradiation has triggered it on.

A LAS is very similar to an SCR, as both are PNPN four layer semiconductor devices. An SCR is normally contained in an opaque case, and is triggered by the application of a small electrical signal to its gate-cathode junction. A LAS, however, has a transparent window in its case and the incidence of light initiates conduction thereof.

In FIG. 8, when the light source 65 is energized and the shutter 66 moved to admit light to the LAS 67, positive current will run from the battery through the gatecathode of SCR l5, resistor 68, LAS 67, capacitor 69, and base-emitter of transistor 25 to ground 25g. The initial surge of this current is limited by resistor 68. The current will trigger both transistor 25 and SCR 15 into simultaneous conduction. When transistor 25 latches on, winding 70 has positive polarity on its dotted side. Its number of turns is such that the voltage now produced slightly exceeds the battery voltage. Thus, diode 71 conducts and assists the current through LAS 67 in charging capacitor 69 until the current through LAS 67 ceases and the LAS resumes its normal nonconductive state.

When time interval 1, has elapsed and t has commenced, all transformer windings reverse their polarity, as does winding 70 which now is negative on its dotted side. This will cause capacitor 72 to be charged via diode 73. The polarity of the voltage across diode 73 is such as to reverse-bias the base-emitter junction of transistor 74 rendering it nonconductive. After termination of time interval t the charge now contained in capacitor 72 drives a base current into transistor 74 by going from plate 72a of capacitor 72 via resistor 75,

base-emitter junction of 74 and Winding 70 (now dormant) to plate 72b of capacitor 72. By this action, transistor 74 is enabled to carry a strong collector-emitter current which will discharge capacitor 69. If at this time the shutter has interrupted the light to the LAS 67, the device is restored to its initial condition and is ready to repeat the sequence as soon as light is admitted by shutter 66.

However, if the light continues to shine on LAS 67 when transistor 74 conducts, the triggering current will turn on both the SCR l5 and the transistor 25. The system will in this case recycle indefinitely and produce a shower of sparks at spark gap 10. This mode of operation may occur during starting (cranking) an engine or even during slow idling. The slot 660 in shutter 66 is narrow enough to shut off the light in the time interval I, when the engine speed is somewhat higher. This ability to provide multiple sparks when cranking will improve the certainty of starting an engine. In all other respects the circuit functions similarly to that disclosed in FIG. 1.

While several embodiments of the invention have been described, it is understood that the particular embodiments of the invention herein disclosed are for illustrative purposes only and that various changes may be made therein without departing from the principles of the invention.

I claim: 1

1. A capacitor discharge ignition system for an internal combustion engine, the combination including, a spark producing circuit having an ignition capacitor, discharging means coupled to said ignition capacitor for discharging the same in synchronism with the engine to produce sparking pulses, said discharging means being activated by the application of a trigger pulse thereto, said discharging means including a semiconductive controller rectifier connected in series with said ignition capacitor, charging means coupled to said ignition capacitor for recharging said capacitor between discharges thereof, said charging means including a saturable pulse transformer means having primary winding means, feedback winding means and secondary winding means, for providing a charging pulse to said ignition capacitor upon the application of a trigger pulse to said transformer means, said charging means including a transistor means connected in series with the primary winding of said saturable transformer means, triggering means coupled to said charging means and said discharging means for simultaneously providing trigger pulses to said charging means and said discharging means so that said charging means is activated simultaneously with the discharging means, said triggering means including capacitor means connected to ground, transistor means coupled with said discharging and said charging means, said transistor means including a first transistor means and a second transistor means, said first transistor means having its collector electrode connected to the base electrode of said second transistor means, said second transistor means having its emitter electrode connected to said capacitor means, its collector electrode connected to the semiconductive controlled rectifier of of said discharging means and its base electrode connected to the transistor of the said charging means, diode means coupled with said discharging'means and said chargning means, said diode means including a first diode means interconnected between the emitter electrode of the first transistor and the emitter electrode of the second transistor whereby the cathode electrode of said first diode means is connected to the emitter electrode of the first transistor, and second diode means interconnected between the base electrode of the second transistor and the collector electrode of the first transistor whereby the cathode electrode of said second diode means is connected to the collector electrode means of the first transistor, and signal means for producing a command pulse coupled to the said first transistor means of the triggering means for providing said simultaneous trigger pulses.

l III 4 l

Claims

1. A capacitor discharge ignition system for an internal combustion engine, the combination including, a spark producing circuit having an ignition capacitor, discharging means coupled to said ignition capacitor for discharging the same in synchronism with the engine to produce sparking pulses, said discharging means being activated by the application of a trigger pulse thereto, said discharging means including a semiconductive controller rectifier connected in series with said ignition capacitor, charging means coupled to said ignition capacitor for recharging said capacitor between discharges thereof, said charging means including a saturable pulse transformer means having primary winding means, feedback winding means and secondary winding means, for providing a charging pulse to said ignition capacitor upon the application of a trigger pulse to said transformer means, said charging means including a transistor means connected in series with the primary winding of said saturable transformer means, triggering means coupled to said charging means and said discharging means for simultaneously providing trigger pulses to said charging means and said discharging means so that said charging means is activated simultaneously with the discharging means, said triggering means including capacitor means connected to ground, transistor means coupled with said discharging and said charging means, said transistor means including a first transistor means and a second transistor means, said first transistor means having its collector electrode connected to the base electrode of said second transistor means, said second transistor means having its emitter electrode connected to said capacitor means, its collector electrode connected to the semi-conductive controlled rectifier of of said discharging means and its base electrode connected to the transistor of the said charging means, diode means coupled with said discharging means and said chargning means, said diode means including a first diode means interconnected between the emitter electrode of the first transistor and the emitter electrode of the second Transistor whereby the cathode electrode of said first diode means is connected to the emitter electrode of the first transistor, and second diode means interconnected between the base electrode of the second transistor and the collector electrode of the first transistor whereby the cathode electrode of said second diode means is connected to the collector electrode means of the first transistor, and signal means for producing a command pulse coupled to the said first transistor means of the triggering means for providing said simultaneous trigger pulses.