Capacitor Discharge Type Ignition System For Internal Combustion Engines

Abstract

In a capacitor discharge type ignition system for internal combustion engines, which generates ignition sparks between electrodes of a spark plug by rapidly discharging a charged capacitor through the primary circuit of an ignition coil, the improvement residing in that the said primary circuit is provided with additional reactance elements so that said reactance elements constitute an oscillation circuit including said primary circuit, to thereby extend the duration of the ignition spark and ensure relative and effective operation of the ignition system.

Description

BACKGROUND OF THE INVENTION:

Field of the Invention

This invention relates to a capacitor discharge type ignition systems for internal combustion engines to control the electric spark caused to bridge the spark plug electrodes for igniting and firing the mixture of gasoline as the fuel and air.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 is a circuit diagram, partly in the block form, showing the conventional capacitor discharge type ignition system;

FIG. 2 is a circuit diagram of an embodiment of the capacitor discharge type ignition system according to the invention;

FIG. 3 is a circuit diagram of a second embodiment of the capacitor discharge type ignition system according to the invention;

FIG. 4 is a circuit diagram showing a modification of the gate circuit in the capacitor discharge type ignition system according to the invention;

FIG. 5 is a circuit diagram showing a modification of the DC-to-DC converter in the capacitor discharge type ignition system according to the invention;

FIG. 6 is a circuit diagram, partly in block form, showing a third embodiment of the capacitor discharge type ignition system according to the invention;

FIG. 7 is a graph showing the waveform of the current through the ignition coil in the embodiment of FIG. 6;

FIG. 8 is a circuit diagram, partly in block form, showing a fourth embodiment of the capacitor discharge type ignition system according to the invention;

FIG. 9 is a graph showing the waveform of the current through the ignition coil in the embodiment of FIG. 8; and

FIGS. 10 to 13 are circuit diagrams, partly in block form, showing further embodiments of the capacitor discharge type ignition system according to the invention.

DESCRIPTION OF THE PRIOR ART

The prior-art ignition system of the type, to which the invention pertains, comprises a DC-to-DC converter to step up a low DC source voltage to a high DC voltage and a capacitor charged and discharged in accordance with the output voltage of the DC-to-DC converter. The discharging circuit of the capacitor is constituted by connecting the primary winding of the ignition coil in series with a switching element such as a silicon controlled rectifier element. Upon triggering of the switching element the charge stored on the capacitor is discharged through the primary winding of the ignition coil to induce a high surge voltage across the secondary winding of the ignition coil. The induced high voltage is applied across the spark plug electrodes, causing an intensitive spark to bridge the gap between the spark plug electrodes to ignite the fuel-air mixture introduced into the cylinder of the internal combustion engine. FIG. 1 shows a typical example of the prior-art ignition system of the type just described. As shown in the figure, it comprises a battery source 1, a DC-to-DC converter 2, a capacitor 3 charged by the output voltage of the DC-to-DC converter 2, an ignition coil 4 having a primary winding 4a, a secondary winding 4b and an iron core 4c, a silicon controlled rectifying element 5 (hereinafter referred to as SCR), a gate circuit 6 delivering the gate signals to the gate of the SCR 5 in synchronism with the rotation of a rotary shaft related in phase to the rotation of the engine crankshaft not shown, and a spark plug 7 provided in the engine.

In the operation of the system just described, the SCR 5 is "off" in the absence of the gate signal at its gate, triggered when it receives the gate signal from the gate circuit 6 and cut off after the gate signal disappears. When the SCR is "off", the capacitor 3 is charged by the output voltage of the DC-to-DC converter 2. Thus, the terminal voltage built up across the capacitor 3 is substantially equal to the output voltage of the DC-to-DC converter 2. In this situation, as soon as the gate circuit 6 generates a gate signal to trigger the SCR 5, the charge accumulated on the capacitor 3 is rapidly discharged through the primary winding 4a of the ignition coil 4 and the SCR 5, thus inducing a high voltage across the secondary winding 4b of the ignition coil 4 to cause a spark between the electrodes of the spark plug 7. Thereafter, the capacitor 3 is reversely charged, that is the polarity of the voltage built up across the capacitor 3 is reversed, owing to the inductance of the primary winding 4a. The current in the primary winding 4a thus does not cease immediately after the capacitor 3 is completely discharged but reversely charges the capacitor 3, as the capacitor 3 and the primary winding 4a constitute a series-resonant circuit. Thus, the current continues to flow in the primary winding 4a in the same direction, until the terminal voltage developed across the capacitor 3 in the polarity opposite to that when the capacitor 3 is being discharged reaches a maximum value, at which time the SCR 5, reversely biased by the terminal voltage of the reversed polarity across the capacitor 3, and undergoes transition into the non-conduction state. At this time, the gate signal from the gate circuit 6 has already disappeared. Also, at this time the spark bridging the electrodes of the spark plug 7 disappears. The reversely charged capacitor 3 is thereafter discharged through the internal circuit of the DC-to-DC converter 2 and then re-charged from the DC-to-DC converter 2. The above sequence of operation is repeated to produce sparks between the electrodes of the spark plug 7 in accordance with the spark timing.

In the ignition system described above, the impedance of the primary winding 4a of the spark coil 4 is made extremely low to cause an extremely high current in the primary winding 4a when the capacitor 3 is discharged upon triggering of the SCR 5, so that a very strong high-voltage spark may be produced across the gap between the electrodes of the spark plug 7. However, as the capacitor 3 is rapidly discharged, the duration of the spark across the electrodes of the spark plug 7 is extremely short. This sometimes results in ignition failure, that is, the spark fails to continue sufficiently long to fire the mixture of fuel and air admitted into the engine cylinder. If the impedance of the primary winding 4a of the spark coil 4 is increased to extend the duration of the spark, however, the ignition current flowing between the electrodes of the spark plug is so decreased as not to ignite the mixture of fuel and air in the engine, particularly when the spark plug electrodes are contaminated with carbon. Also, since most of the energy stored in the ignition coil 4 as the capacitor 3 is discharged is consumed in producing the spark, only a fraction of the energy transferred to the ignition coil 4 is returned to the capacitor 3, so that the reverse terminal voltage across the capacitor 3 reversely biasing the SCR 5 is sometimes insufficient to cut off the SCR 5. If the SCR fails to be cut off and continues to be "on", the capacitor 3 cannot be re-charged in the next re-charging cycle, and only a constant current determined by the DC-to-DC converter 2 and the charging and discharging circuit flows through the primary winding 4a of the ignition coil 4. In this case, even if the gate circuit 6 delivers a gate signal to the SCR 5 in the condition state, a surge current will not be caused in the primary winding 4a of the ignition coil 4, since the capacitor 3 has not been charged but the constant current determined by the DC-to-DC converter 2 and the charging and discharging circuit has been flowing through the primary winding. Consequently, no high voltage is induced across the secondary winding 4b of the ignition coil 4 and no spark is produced across the electrodes of the spark plug 7, which is a serious disadvantage.

SUMMARY OF THE INVENTION

A principal object of the invention is to overcome the above disadvantages of the prior-art ignition system, that is, to sufficiently extend the duration of the spark and ensure the transition of the switching element into the non-conduction state after the extinction of the initial spark.

To achieve these ends, according to the invention there is provided a capacitor discharge type ignition system comprising a capacitor charged by the output voltage of a DC-to-DC converter, and a discharging circuit, through which the capacitor is discharged, and which includes the primary winding of the spark coil and a switching element connected in series with the primary winding and having a gate, wherein the charging circuit further includes at least one additional capacitor and at least one additional inductor coil to constitute an electric pulsation circuit together with the primary winding of the ignition coil, thereby extending the duration of the discharge current flowing through the primary winding of the ignition coil by a predetermined time interval.

These and other objects, features and effects of the invention will become more apparent from the following description of the preferred embodiments of the invention with reference to the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Throughout the drawing like component parts are designated by like reference numerals or symbols.

Referring now to FIG. 2, which shows a first embodiment of the capacitor discharge type ignition system according to the invention, numeral 11 designates a battery source and numeral 12 a blocking oscillator type DC-to-DC converter to step up the low DC voltage of the battery source 11 into a high DC voltage. The DC-to-DC converter 12 comprises a bias resistor 12a, a transistor 12b, a feedback resistor 12c, a feedback capacitor 12 d, a transformer 12e, and a capacitor 12f to mitigate the spike voltage induced across the secondary of the transformer 12e. Numeral 13 designates a first capacitor charged with the output voltage of the DC-to-DC converter 12, numeral 14 a diode, numeral 15 a second capacitor, and numeral 16 a saturable reactor. Numeral 17 designates an ignition coil including a primary winding 17a, a secondary winding having several ten times the number of turns of the primary and an iron core 17c. Numeral 18 designates a spark plug provided in an engine cylinder not shown for igniting the air-fuel mixture admitted into the cylinder. Numeral 19 designates an SCR, which is triggered to cause discharging of the electricity stored in the first capacitor 13 so as to provide current through the second capacitor 15 and the primary winding 17a of the ignition coil 17. Numeral 20 designates a gate circuit to deliver a gate signal (trigger signal) to the gate of the SCR 19. It comprises a switch 20a on-off operated by a shaft means (not shown) rotated in association with the engine crankshaft, a discharging resistor 20b, a capacitor 20c, a diode 20d and a current-regulating resistor 20e.

The operation of the ignition system just described, as the switch 20a, which is assumed to be open at the outset, is switched into the "on" state and then into the initial "off" state by the rotation of the rotary shaft in association with the engine crankshaft, will now be described in the mentioned order. While the switch 20a is open, the output voltage of the DC-to-DC converter 12 charges the first capacitor 13 to build up a high voltage thereacross. Since the switch 20a is open, the gate circuit 20 produces no gate signal, so that the SCR 19 is "off". In this situation, no current flows either in the saturable reactor 16 or in the primary winding 17a of the ignition coil 17, and the second capacitor 15 is not charged. Also, in this situation no spark is present across the electrodes of the spark plug 18. This situation holds until the switch 20a is closed, whereupon a gate signal current is caused to flow from the battery source 11 through the capacitor 20c and resistor 20e into the gate of the SCR 19, thus triggering the SCR 19. As a result, the charge accumulated in the first capacitor 13, developing a high voltage, is rapidly discharged through the discharging path consisting of the second capacitor 15, the primary winding 17a of the ignition coil 17 and the SCR 19. Although the discharging current from the first capacitor 13 partially flows through the other discharging path consisting of the diode 14 and the saturable reactor 16, a substantial part of the discharging current from the first capacitor 13 passes through the primary winding 17a of the ignition coil 17, because the reactance offered by the saturable reactor 16 is made large compared to the reactance offered by the primary winding 17a of the ignition coil 17. The large current flowing through the primary winding 17a of the ignition coil 17 thus induces a high surge voltage across the secondary winding 17b to produce a strong high-voltage spark bridging the electrodes of the spark plug 18. Subsequently, the second capacitor 15 begins to store charge, and a great quantity of charge is transferred from the first capacitor 13 to the second capacitor 15 and stored therein. The gate signal current to the SCR 19 is present only for a short time determined by the capacitor 20c and the resistor 20e of the gate circuit 20, and is already absent by the time the second capacitor 15 is charged to a maximum, at which time the current through the primary winding 17a of the ignition coil 17 is reduced to zero. The SCR 19 is cut off when the reverse bias voltage thereacross reaches a predetermined value, and is thereafter maintained "off" until a next gate signal appears at its gate. The charge built up in the second capacitor 15 is thus discharged through the diode 14, saturable reactor 16 and primary winding 17a of the ignition coil 17. The duration of this discharging is comparatively longer by virtue of a high reactance offered by the saturable reactor 16. The direction of the discharging current from the second capacitor 15 through the primary winding 17a of the ignition coil 17 is opposite to the direction of the discharging current caused from the first capacitor through the primary winding 17a of the ignition coil 17 upon triggering of the SCR 19. The spark caused across the electrodes of the spark plug 18 temporarily ceases at the time the direction of current through the primary winding 17a of the ignition coil 17 is inverted, but it is readily resumed with a fairly low voltage after the inversion of the direction of current through the primary winding 17a by virtue of the fact that ions produced by the previous sparking remain around the electrodes of the spark plug 18. The duration of the resumed spark is comparatively longer because of a relatively long period, during which the discharging current from the second capacitor 15 flows through the primary winding 17a of the ignition coil 17, thus insuring stable ignition of the air-fuel mixture. The first capacitor 13 begins to be re-charged by the output voltage of the DC-to-DC converter 12 when the SCR 19 is cut off, and the system becomes ready for the impression of a next gate signal on the gate of the SCR 19.

When the switch 20a of the gate circuit 20 is re-opened, the charge stored on the capacitor 20c is discharged through the discharging resistor 20b and the diode 20d to provide a trigger signal to the gate of the SCR 19. The above sequence of events is repeated to produce interelectrode sparks at the spark plug 18 in synchronism with the ignition timing for igniting and combusting the air-fuel mixture in the engine cylinder.

The duration of the spark caused by the discharging of the second capacitor 15 may be set to a suitable value by varying the reactance of the saturable reactor 16. This means that the diode 14 may be dispensed with if the period of the pulsating current is made sufficiently short as compared to the ignition cycle.

FIG. 3 shows a second embodiment of the ignition system according to the invention. In this embodiment, the primary winding of the ignition coil 17 is tapped at (a) for connection to the anode of the SCR 19.

In the operation of this construction, when the SCR 19 is triggered, the charge on the first capacitor 13 is discharged through the second capacitor 15, the primary winding portion 17a of the ignition coil 17 and the SCR 19 to induce a high voltage across the secondary winding 17b of the ignition coil 17, thus producing an interelectrode spark at the spark plug 18. The voltage drop across and the duration of the spark thus produced are apparently the same as those in the operation of the first embodiment. However, as the charge accumulated on the second capacitor 15 during the discharging of the first capacitor 13 is discharged through the diode 14, the saturable reactor 16, the auxiliary primary winding portion 17d and the primary winding portion 17a, the overall duration of the interelectrode spark caused this time at the spark plug 18 is extended beyond that in the operation of the first embodiment by an interval corresponding to the reactance of the auxiliary primary winding portion 17d. Thus, the duration of the spark caused by the discharging of the second capacitor 15 may be suitably set by varying the reactance of the saturable reactor 16 and that of the auxiliary primary winding portion 17d.

The gate control circuit 20 in the preceding embodiments of FIGS. 2 and 3 may be replaced with the one shown in FIG. 4. In this gate circuit, as a rotary magnet 20f is rotated in association with the engine crankshaft, high surge voltages are induced across a generator winding 20g to switch a transistor 20h. The switching of the transistor 20h gives rise to square-wave pulses at the collector thereof, which are differentiated by a differentiating circuit including a capacitor 20i and a resistor 20j to produce positive differentiated pulses. The resultant differentiated pulses are delivered as the gate signal to the gate of the SCR 19.

The DC-to-DC converter 12 in the preceding embodiments of FIGS. 2 and 3 may be replaced with the one shown in FIG. 5. As shown in the figure, it may be of the electromagnetic feedback self-sustaining multivibrator type, comprising a pair of transistors 12h and 12i, which are self-oscillated by the alternate positive feedback through a transformer 12j. In the DC-to-DC converter 12 of this type, the spike voltage removal capacitor 12 provided in the preceding embodiments of FIGS. 2 and 3 is unnecessary. Also, as the switching element to cause the discharging of the first capacitor 13 through the second capacitor 15 and the primary winding 17a of the ignition coil 17, the SCR 19 in the above embodiments of FIGS. 2 and 3 may be replaced with other semiconductor switching elements such as transistors or mechanical contact means.

FIG. 6 shows a third embodiment of the invention. As is seen from the figure, this embodiment is similar to the embodiment of FIG. 2 except for that a silicon symmetrical switch 22 (hereinafter referred to as SSS) is connected in parallel with the diode 14. In the embodiment of FIG. 2, the circuit consisting of the second capacitor 15, winding 17a, saturable reactor 16 and diode 14 cannot provide sustained electric oscillation because of the diode 14 connected in series therein. This means that current is caused through the primary winding 17a of the ignition coil 17 only twice in one ignition cycle. On the other hand, in the third embodiment of FIG. 6 by virtue of the bidirectional SSS 22 connected in parallel with the diode 14 alternate charging and discharging of the second capacitor 15 is repeated subsequent to a short period of conduction of the SCR 19, thus causing an alternating current in the primary winding 17a of the ignition coil 17. This alternating current, however, is gradually attenuated due to resistive loss in the charging and discharging circuit. Stated in another way, an attenuating oscillation is generated in the charging and discharging circuit subsequent to the cutting-off of the SCR 19. The peak terminal voltage across the second capacitor 15 for every half cycle of oscillation in one ignition cycle is successively decreased, and when the peak voltage across the capacitor 15 becomes too low for the SSS to breakdown, the SSS 22 is no longer triggered, so that the electric oscillation in the afore-said circuit ceases. When this situation is brought about, the capacitor 15 always has its terminal connected to the primary winding 17a of the ignition coil 17 positively polarized by virtue of the diode 14. As the attenuating alternating current flows through the primary winding 17a of the ignition coil 17, a corresponding attenuating alternating voltage is induced across the secondary winding 17b to cause a corresponding attenuating alternating arc current, i.e., the spark, through the gap between the electrodes of the spark plug 18. Thus, in the third embodiment the overall spark duration in one ignition cycle is extended as compared to the first embodiment.

In the above embodiments, the circuit parameters of the discharging circuit, through which the capacitor 13 is discharged, are preset to provide an appropriate duration of the attenuating oscillation in this circuit. The sufficient duration of the arc current between the electrodes of the spark plug in one ignition cycle is about 1 to 1.5 msec. Extending the duration of the arc current beyond this range by increasing the duration of the attenuating electromagnetic oscillation in the discharging circuit is useless and results in an increased power loss in the discharging circuit. Besides, if the duration of the attenuating oscillation, and hence the arc current, is not appropriately limited, the SCR 19 might be triggered for the next ignition cycle while there is still discharging current flowing from the second capacitor 15 through the diode 14, saturable reactor 16 and winding 17a. If this occurs, all the current from the DC-to-DC converter 12 and from the first capacitor 13 will flow through the route of the diode 14 and saturable reactor 16 into the SCR 19, causing no current through the primary winding 17a of the ignition coil 17 and hence no spark between the electrodes of the spark plug 18, thus resulting in ignition failure and eventually stopping the engine as this undesired situation takes place in the succeeding ignition cycles. This result is prevented by setting the duration of the attenuating electric oscillation in one ignition cycle to be 1 to 1.5 msec. as mentioned above, because the period of the ignition cycle is usually 2.5 to 3 msec.

FIG. 7 shows the waveform of the current through the primary winding 17a of the ignition coil 17 in the third embodiment. Current as indicated at (a) first flows through the primary winding 17a upon triggering of the SCR 19, and current as indicated at (b), (c), (d), (e) and (f) is subsequently caused to flow through the primary winding 17a by the attenuating electric oscillation in the circuit including the second capacitor 15, primary winding 17a and saturable reactor 16. As is seen from the figure, the current through the primary winding 17a of the ignition coil 17 is not continuous but pulsating or intermittent involving non-current intervals as indicated at (a'), (b'), (c'), (d') and (e'). This is attributable to a high impedance of the saturable reactor 16 offered when the saturable reactor 16 is not saturated while the current in the resonant circuit is less than a predetermined value. In effect, the current in the resonant circuit is restricted to a very small value until the core of the saturable reactor 16 is saturated. The electric oscillation would be continued to provide current as indicated at (g), (h) and (i), if the SSS 22 is short-circuited. By the action of the SSS 22, however, the electric oscillation continues only for an interval t.sub.a, and thereafter the peak value of the terminal voltage across the second capacitor 15 is no longer higher than the breakdown voltage of the SSS 22 and the electric oscillation ceases.

FIG. 8 shows a fourth embodiment of the ignition system according to the invention. This embodiment is similar to the third embodiment of FIG. 6 except for that in this embodiment a third capacitor 23 and a reactor 24 are connected to the output terminal of the DC-to-DC converter 12 and the first capacitor 13 is charged through the reactor 24.

To simplify the description, the resonant circuit comprising the second capacitor 15, primary winding 17a of the ignition coil 17, saturable reactor 16, diode 14 and SSS 22 is referred to as the first resonant circuit, and the resonant circuit comprising the third capacitor 23, reactor 24 and first capacitor 13 is referred to as the second resonant circuit. The period of oscillation of the second resonant circuit is determined by the capacitance of the first and third capacitors 13 and 23 and the inductance of the reactor 24. The electric oscillation in the first resonant circuit brings about periodic change of the terminal voltage across the first capacitor 13. As the first and second resonant circuits are connected to each other, they interfere with each other. As a result, the waveform of the electric oscillation in the second resonant circuit, that is, the current through the primary winding 17a of the ignition coil 17, is quite different from that described in connection with FIG. 7.

FIG. 9 shows such waveform of the current through the primary winding 17a of the ignition coil 17. In the Figure, A indicates current caused to pass through the primary winding 17a upon the triggering of the SCR 19, and B, C, D, E, F, G, H, I, J, K and L indicate the subsequent pulsating current through the primary winding 17a. As is seen, the oscillation is not a purely attenuating oscillation owing to the interfering influence of the second resonant circuit on the oscillation of the first resonant circuit. Similar to FIG. 7, reference symbols A', B', C', D', E', F', G', H', I', J' and K' indicate non-current intervals, during which negligeble current flows through the second resonant circuit because of a high impedance offered by the non-saturated saturable reactor 16. In FIG. 9, time interval t.sub.a corresponds to the duration of the oscillation in the third embodiment of FIG. 6, and time interval t.sub.b is the overall duration of the oscillation in the fourth embodiment of FIG. 8.

FIG. 10 shows a fifth embodiment of the invention. This embodiment includes a circuit having a breakdown character, which comprises a zener diode 22b and an SCR 22d and replaces the SSS 22 in the embodiment of FIG. 8. The operation of this embodiment is similar to the operation of the embodiment of FIG. 8. When the terminal voltage across the SCR 22d exceeds the zener voltage of the zener diode 22b, the zener diode is triggered to provide a voltage divided between resistors 22a and 22c to the gate of the SCR 22d, thus triggering the SCR 22d. When the SCR 22d is triggered, the zener diode 22b is short-circuited and the gate voltage disappears, but the SCR 22d continues to carry current until the forward voltage thereacross becomes very low. It will be seen that the zener voltage of the zener diode 22b in this embodiment corresponds to the breakdown voltage of the SSS 22 in the previous embodiment.

FIG. 11 shows a sixth embodiment of the invention. In this embodiment, the function of the first and second capacitors 13 and 15 is the same as in the preceding embodiments. This embodiment includes a third capacitor 25, a first saturable reactor 26 and a second saturable reactor 27.

In the operation of this embodiment, while the gate signal from the gate circuit 20 is absent at the gate of the SCR 19, the first capacitor 13 is charged to develop a high voltage by the output voltage of the DC-to-DC converter 12. During this time, as the SCR 19 is "off", no current is present in the first and second saturable reactors 26 and 27 and the primary winding 17a of the ignition coil 17. Also, no charge is stored on the second and third capacitors 15 and 25. In this situation, when the gate circuit 20 delivers a gate signal to trigger the SCR 19, the charge accumulated on the first capacitor 13 to develop a high voltage is rapidly discharged through the route consisting of the second capacitor 15, winding 17a and SCR 19 and the route consisting of the third capacitor 25, the first saturable reactor 26 and the SCR 19. Although the second saturable reactor 27 constitutes a third route of discharge of the capacitor 13, most of the discharging current from the first capacitor 13 passes through the route respectively consisting of the primary winding 17a of the ignition coil 17 and the saturable reactor 26, because the reactance of the second saturable reactor 27 is greater than the reactance of either the winding 17a or the first saturable reactor 26. The current passing through the primary winding 17a induces a high voltage across the secondary winding 17b of the ignition coil 17 to produce a high-tension spark bridging the electrodes of the spark plug 18. The polarity of the first capacitor 13 is subsequently reversed owing to the electric oscillation of the resonant circuit consisting of the third capacitor 25 and first saturable reactor 26, and the second and third capacitors 15 and 25 begin to store charge. By this time, the gate signal to the SCR 19 has already disappeared. By the time the charging of the second and third capacitors 15 and 25 is completed and the current through the primary winding 17a of the ignition coil 17 and the first saturable reactor 26 ceases, the SCR 19 is cut off as it is reversely biased with the reverse voltage developed on the first capacitor 13, and it remains until a subsequent gate signal is impressed on its gate. During the non-conduction of the SCR 19, the charge stored in the second and third capacitors 15 and 26 causes oscillatory currents to flow through the first and second saturable reactors 26 and 27 and the primary winding 17a of the ignition coil 17 to cause an extended pulsating arc current to pass across the gap between the electrodes of the spark plug 18 until the oscillatory current is attenuated to a certain level. After the cutting-off of the SCR 19, the first capacitor 13 begins to be charged by the output voltage of the DC-to-DC converter 12. The above sequence of events is repeated as the gate circuit 20 delivers successive gate pulse signals at a predetermined pulse frequency.

The duration of the pulsating current, or the duration of the spark, may be suitably preset by appropriately varying the capacitance of the second and third capacitors 15 and 25 and the inductance of the first and second saturable reactors to vary the frequency of the electric oscillation.

FIG. 12 shows a seventh embodiment of the invention. In the figure, numeral 28 designates a first reactor, numeral 29 a third capacitor charged by the output voltage of the DC-to-DC converter 12 through the first reactor 28, and numeral 30 a second reactor. The function of the first and second capacitors 13 and 15 and other similar components to those in the preceding embodiments is the same as described earlier.

In the operation of this embodiment, while the gate signal from the gate circuit 20 is absent at the gate of the SCR 19, the first and third capacitors 13 and 29 are charged to develop a high voltage by the output voltage of the DC-to-DC converter 12. As during this time the SCR is "off", no current is present in the second reactor 30 and the primary winding 17a of the ignition coil 17. Also, no charge is stored on the second capacitor 15. In this situation, when the gate circuit 20 delivers a gate signal to trigger the SCR 19, the charge accumulated on the first capacitor 13 to develop a high voltage is rapidly discharged through the route of the second capacitor 15, primary winding 17a of the ignition coil 17 and SCR 19. At the same time, the charge accumulated on the third capacitor 29 is also discharged through the second reactor 30 and SCR 19. Although the series connection of the first and second reactors 28 and 30 constitute a second route of discharge of the first capacitor 13, most of the discharging current from the first capacitor 13 passes through the route of the primary winding 17a of the ignition coil 17, because the resultant reactance of the first and second reactors 28 and 30 is great as compared to the reactance of the winding 17a. The current passing through the primary winding 17a of the ignition coil 17 induces a high voltage across the secondary winding 17b thereof to produce a high-tension spark bridging the electrodes of the spark plug 18. The discharging current from the third capacitor 29 through the second reactor 30 and SCR 19 induces back electromotive force in the second reactor 30, and by virtue of the electric momentum involved the third capacitor 29, having been completely discharged, begins to be reversely charged. Similarly, more charge than the charge accumulated on the first capacitor is transferred to the second capacitor 15. By this time, the gate signal from the gate circuit 20 has already ceased. Thus, the SCR 19 is eventually cut off as it is reversely biased with the negative or reverse voltage developed on the first capacitor 13, and it is held "off" until a subsequent gate signal is impressed on its gate. During the non-conduction of the SCR 19, the charge stored on the second capacitor 15 causes an oscillatory current through the first and second reactors 28 and 30 and the primary winding 17a of the ignition coil 17. Also, the charge stored on the third capacitor 29 gives rise to electric oscillation in the circuit consisting of the first reactor 28, the second capacitor 15, the winding 17a and the second reactor 30. Further electric oscillation takes place in the circuit of the first capacitor 13 and the first reactor 28. These electric oscillations interfere with one another to cause a pulsating current in the primary winding 17a of the ignition coil 17 for an extended period of time, thus causing an extended pulsating arc current through the gap between the electrodes of the spark plug 18. After the cutting-off of the SCR 19, the first and third capacitors 13 and 29 begin to be charged by the output voltage of the DC-to-DC converter 12. The above sequence of events is repeated as the gate circuit 20 delivers successive trigger pulses at a predetermined pulse frequency.

The duration of the pulsating arc current may be suitably preset by appropriately varying the capacitance of the first, second and third capacitors 13, 15 and 29 and the inductance of the first and second reactors 28 and 30.

FIG. 13 shows an eighth embodiment of the invention. In the figure, numeral 31 designates a first reactor, numeral 32 a second capacitor charged by the output voltage of the DC-to-DC converter 12 through the first reactor 31, numeral 33 a second reactor, and numeral 34 a third capacitor. The function of the other components is the same as in the preceding embodiments.

In the operation of this embodiment, while the gate signal from the gate circuit 20 is absent at the gate of the SCR 19, the SCR 19 is "off" and the first, second and third capacitors 13, 32 and 34 are charged to a high voltage by the output voltage of the DC-to-DC converter 12. In this situation, when the gate circuit 20 delivers a gate signal to trigger the SCR 19, the charge accumulated on the second capacitor 32 to develop a high voltage is rapidly discharged directly through the primary winding 17a of the ignition coil 17. Simultaneously, the charge on the first capacitor is discharged through the first reactor 31, the primary winding 17a of the ignition coil 17 and the SCR 19. Thus, the discharging current from the first capacitor 13 is superimposed in the primary winding 17a of the ignition coil 17 upon the discharging current from the second capacitor 32. The first capacitor 13 is however discharged more slowly as compared to the second capacitor 32 because of the reactance of the first reactor 31. As the charge on the second capacitor 32 rushes into the primary winding 17a of the ignition coil 17, a very high surge voltage is induced across the secondary winding 17b of the ignition coil 17 to very promptly cause a strong spark to pass between the electrodes of the spark plug 18. This strong spark does not momentarily disappear, but is prolonged for a certain interval of time by virtue of the superimposed discharging current from the first capacitor 13, which is caused to pass more gradually through the primary winding 17a of the ignition coil 17. On the other hand, the discharging current from the third capacitor 34 through the second reactor 33 and the SCR 19 induces back electromotive force in the second reactor 33, and the third capacitor 34, having been completely discharged, begins to be reversely charged. By this time, the gate signal from the gate circuit 20 has already ceased. Thus, the SCR 19 is eventually cut off as it is reversely biased with the negative voltage developed on the third capacitor 34, and it is held "off" until a subsequent gate signal is impressed on its gate. During the non-conduction of the SCR 19, the charge stored on the second capacitor 32 gives rise to the electric oscillation in the first closed circuit consisting of the primary winding 17a of the ignition coil 17, the second reactor 33 and the third capacitor 34. Even if the charge on the second capacitor 32 is used too much at the time of the initial discharging through the primary winding 17a of the ignition coil 17 to bring about effective electric oscillation, the remaining charge on the first capacitor 13, the energy stored in the first reactor 31 at the time of the initial discharging of the first capacitor 13 and the charge on the third capacitor 34 are effective to produce electric oscillation in the second closed circuit consisting of the first capacitor 13, first reactor 31, primary winding 17a of the ignition coil 17, second reactor 33, and third capacitor 34 and in the third closed circuit consisting of the first capacitor 13, first reactor 31, and second capacitor 32. Thus, even if the above-mentioned first closed circuit is incapable of producing effective electric oscillations by itself from the above grounds, the electric oscillation of the second and third closed circuits brings about effective electric oscillation in the first closed circuit. Thus, the electric oscillations in the first, second and third closed circuits interfere with one another. Thus, after the cutting-off of the SCR 19, electric oscillations cause a pulsating current to pass through the primary winding 17a of the ignition coil 17 to induce pulsating high voltages in the secondary winding 17a of the ignition coil 17, thus causing a pulsating arc current through the gap between the electrodes of the spark plug 18. As the pulsating arc current between the electrodes of the spark plug 18 is extended, the ignition of the air-fuel mixture introduced into the cylinder is ensured. When the pulsating current flowing in the primary winding 17a of the ignition coil 17 has been attenuated to a predetermined level, the voltage induced across the secondary winding 17b of the ignition coil 17 becomes insufficient to cause a spark to bridge the electrodes of the spark plug 18, so that the spark pulsation ceases. Subsequently, the first, second and third capacitors 13, 32 and 34 are charged by the output voltage of the DC-to-DC converter 12. The above sequence of events is repeated as the gate circuit 20 delivers successive trigger pulses at a predetermined pulse frequency.

Claims

What is claimed is:

1. A capacitor discharge type ignition system for internal combustion engine comprising a DC-to-DC converter, a first capacitor charged by the output voltage of said DC-to-DC converter, a discharging circuit, through which said first capacitor is discharged, said discharging circuit comprising a second capacitor, the primary winding of an ignition coil and a switching element connected in series with one another, and a reactor connected across the said series connection of said primary winding and said second capacitor such that said second capacitor is discharged through said reactor and primary winding in the direction opposite to the direction of discharging of said first capacitor through the primary winding.

2. A capacitor discharge type ignition system according to claim 1 wherein said reactor is a saturable reactor.

3. A capacitor discharge type ignition system comprising a DC-to-DC converter, a first capacitor charged by the output voltage of said DC-to-DC converter, a first discharging circuit, through which said first capacitor is discharged to cause a spark at a spark plug, said first discharging circuit including a second capacitor, the primary winding of an ignition coil and a switching element, a second discharging circuit, through which said second capacitor is discharged, said second discharging circuit including a diode, a reactor and said primary winding, wherein the discharging circuit for the discharge of said second capacitor after the reversal of the polarity of said second capacitor is formed by said primary winding, said reactor and a switching means having a breakdown character.

4. A capacitor discharge type ignition system according to claim 3, wherein said reactor is a saturable reactor.

5. A capacitor discharge type ignition system comprising a DC-to-DC converter, a first capacitor charged by the output voltage of said DC-to-DC converter and discharged through the primary winding of an ignition coil and a switching element to cause a spark at a spark plug, wherein a second capacitor, said primary winding and said switching element form a first discharging circuit, through which said first capacitor is discharged, a diode, a first reactor and said primary winding form a second discharging circuit, through which said second capacitor is discharged, and said primary winding, said reactor and a switching means having an opposite breakdown character with respect to said diode form a third discharging circuit, through which said second capacitor after the reversal of the polarity thereof is discharged, said ignition system further including a second reactor connected between said first capacitor and the output terminal of said DC-to-DC converter and a third capacitor connected to the connection between the output terminal of said DC-to-DC converter and said second reactor and charged by the output voltage of said DC-to-DC converter.

6. A capacitor discharge type ignition system according to claim 5, wherein said first reactor is a saturable reactor.

7. A capacitor discharge type ignition system comprising a DC-to-DC converter, a first capacitor charged by the output voltage of said DC-to-DC converter, a discharging circuit, through which said first capacitor is discharged, said discharging circuit including a second capacitor, the primary winding of an ignition coil and a switching element connected in series, a first reactor connected in parallel with the series circuit of said second capacitor and said primary winding, and a series circuit including a third capacitor and a second reactor, said last-mentioned series circuit being connected in parallel with the series circuit of said second capacitor and said primary winding.

8. A capacitor discharge type ignition system according to claim 7, wherein said first and second reactors are saturable reactors.

9. A capacitor discharge type ignition system comprising a DC-to-DC converter, a first capacitor charged by the output voltage of said DC-to-DC converter, a discharging circuit, through which said first capacitor is discharged, said discharging circuit including a second capacitor, the primary winding of an ignition coil and a switching element connected in series, a first reactor connected to the output terminal of said DC-to-DC converter, a third capacitor charged by the output voltage of said DC-to-DC converter through said first reactor, and a second reactor connected between the connection between said first reactor and said third capacitor and the connection between said primary winding and said switching element.

10. A capacitor discharge type ignition system according to claim 9, wherein said first reactor is saturable reactor.

11. A capacitor discharge type ignition system comprising a DC-to-DC converter, a first capacitor charged by the output voltage of said DC-to-DC converter, a discharging circuit, through which said first capacitor is discharged, said discharging circuit including a first reactor, the primary winding of an ignition coil and a switching element is connected in series, a first series circuit including said first reactor and a second capacitor and connected in parallel with said first capacitor, and a second series circuit including a second reactor and a third capacitor and connected in parallel with said switching element.

12. A capacitor discharge type ignition system comprising:

a DC-to-DC converter,

at least one first capacitor charged by the output voltage of said DC-to-DC converter,

a series circuit including an ignition coil primary winding and a switching device adapted to be turned on and off,

a main circuit, including said series circuit, through which the charge stored in said capacitor is discharged when said switching device is on for producing current through said primary winding, and

an oscillation circuit including a series connection of a second capacitor, an inductive reactance and said primary winding for prolonging the duration of current through said primary winding beyond the turning off of said switching device.

13. An ignition system as in claim 12 including a bidirectional switch in said series connection of said oscillation circuit.

14. An ignition system as in claim 12 including a second inductive reactance serially connected between said converter and first capacitor and a third capacitor connected in parallel across said first capacitor ahead of said second inductive reactance.

15. An ignition system as in claim 12 wherein said second capacitor is in said series circuit between said first capacitor and primary winding.

16. An ignition system as in claim 15 including a second series circuit connected across said inductive reactance and including a third capacitor and a second inductive reactance.

17. An ignition system as in claim 15 including a second inductive reactance and a third capacitor, said second reactance being connected to the first mentioned reactance in said series connection of said oscillation circuit with said third capacitor being connected to the junction between said reactances.

18. An ignition system as in claim 12 wherein said second capacitor and reactance are in parallel with said switching element.

19. An ignition system as in claim 18 and further including a second inductive reactance connected in said series circuit and a third capacitor connected in parallel with said first capacitor.

20. A capacitor discharge type ignition system comprising:

a DC-to-DC converter;

at least one first capacitor charged by the output voltage of said DC-to-DC converter;

A discharging circuit through which the charge stored in said first capacitor is discharged; said discharging circuit including said first capacitor, a primary winding of an ignition coil, a switching element having a gate, at least one second capacitor and at least one reactor, said discharging circuit including:

a circuit through which the charge stored in said first capacitor is supplied via said primary winding to said switching element connected in series with said primary winding, and

an oscillation circuit including said primary winding, said reactor and said second capacitor for prolonging the duration of the discharge current flowing through said primary winding even when the gate of said switching element is closed after the charge of said first capacitor has been transferred to said switching element through said primary winding.