US 3736463 A
A silicon controlled rectifier controls a capacitor discharge into an electronic ignition circuit for internal-combustion engines. Spurious signals are prevented from operating the controlled rectifier.
Description (OCR text may contain errors)
United States Patent [191 Basso et al.
[ 1 May 29, 1973  ELECTRONIC DEVICE FOR CONTROLLING A SILICON CONTROLLED RECTIFIER IN A CAPACITOR DISCHARGE ELECTRONIC IGNITION CIRCUIT  Inventors: Eugenio Basso, Levico; Giacomo Gulino, Monza; Antonio Veronese, Padova, all of Italy  Assignee: Fabbrica Italiana Magneti Marelli S.p.A., Milan, Italy 22 Filed: June7, 1971  Appl.No.: 150,466
 Foreign Application Priority Data June 5, 1970 Italy ..25544 A/70  US. Cl. ..315/209 SC, 123/148 E, 315/209 T, 315/209 CD  Int. Cl. ..H03k 17/56  Field of Search ..3l5/209 R, 209 T, 315/209 CD, 209 M, 209 SC; 123/148 R, 148 E  References Cited UNITED STATES PATENTS 7 3,472,216 10/1969 Clyborne ..315/209 SC 3,312,860 4/1967 Sturm ..3l5/209 SC 3,383,556 5/1968 Tarter ..l23/148 E 3,550,571 12/1970 Mainprize... ....l23/148 E 3,587,552 6/1971 Varaut ..315/209 X Primary Examiner-John Zazworsky Att0rney0strolenk, Faber, Gerb & Soffen  ABSTRACT A silicon controlled rectifier controls a capacitor discharge into an electronic ignition circuit for internal-combustion engines. Spurious signals are prevented from operating the controlled rectifier.
7 Claims, 3 Drawing Figures Patented May 29,1973 r 3,736,463
2 Sheets-Sheet 1 FIG. 1
Patented May 29, 1973 2 Sheets-Sheet 2 Var [all ||||L ELECTRONIC DEVICE FOR CONTROLLING A SILICON CONTROLLED RECTIFIER IN A CAPACITOR DISCHARGE ELECTRONIC IGNITION CIRCUIT BRIEF SUMMARY OF THE INVENTION As well known, a silicon controlled rectifier can be used to control a capacitor discharge through the primary winding of an ignition coil. The secondary winding of the coil then provides high voltage to the spark plugs through the distributor.
In such ignition circuits, however, particularly when mounted in motor vehicles, the battery voltage is constant during engine operation, but undergoes abrupt changes under high current drains and fluctuates due to inductances in the converter circuit supplying charging energy to the capacitor.
In addition, high voltage transient pulses will appear in the ignition circuit due to bouncing of the breaker contacts (or points) immediately after their normal closing, partiularly at high engine speeds. Such voltage fluctuation and transient voltage pulses may cause the undesired triggering of the silicon controlled rectifier whereby capacitor discharge takes place (and thus an ignition spark on the spark plugs) at times which do not correspond to the opening of the breaker contacts, with obvious adverse results on the engine efficiency.
The present invention provides a novel circuit for controlling a silicon controlled rectifier, which is unaffected by unwanted transient signals, to assure efficient ignition timing.
The novel control circuit of the invention includes a monostable multivibrator, the output of which is coupled to the control electrode (or gate) of the controlled rectifier. The input of the multivibrator is connected to a capacitive coupling circuit which receives a control signal from a clipping circuit which is, in turn, controlled by the breaker contacts. The entire circuit is then energized from the vehicles starting battery.
The capacitive coupling circuit connected to the multivibrator input serves to block unwanted signals from entering the multivibrator control circuits.
In accordance with another aspect of the invention, a memory circuit is connected to the emitter of an input transistor of the multivibrator to prevent operation of the multivibrator by signals unrelated to the closing of the timing contacts.
According to a still further aspect of the invention, the circuit connecting operating voltage to the multivibrator includes an integrating circuit capable of supplying the multivibrator with a sufficiently high voltage at the proper ignition instant while permitting the existence of a lower voltage at other times.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram partly in block form of a capacitor discharge operated electronic ignition circuit provided with a silicon controlled rectifier for the capacitor discharge;
FIG. 2 is a diagram of the control circuit for controlling the silicon controlled rectifier according to the invention; and
FIGS. 3, a tofshow voltage wave shapes, during an operation cycle, at certain points in the circuit of FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, there is shown a converter or a-c generator 1 which may be driven by the battery of the vehicle (not shown), a coupling transformer 2, a capacitor 3, a rectifier diode 4, an ignition coil 5 and a terminal 6 of the coil secondary winding which is connected directly to the ignition distributor (not shown). Normally, capacitor 3 is charged from converter 1 through diode 4. FIG. 1 also shows a further diode 7 and a resistor 8, as well as a silicon controlled rectifier 20 controlled by the electronic control circuit 9 in accordance with the present invention.
Capacitor 3 is conventionally discharged through the primary winding of coil 5 when controlled rectifier 20 is fired. Hence the ignition takes place when the control circuit 9 supplies a triggering signal to the controlled rectifier 20.
The invention provides a novel control device capable of supplying said triggering signal only at each normal opening of the breaker contacts which conventionally provide ignition timing.
To this end, and referring to FIG. 2, the control circuit 9 includes a monostable multivibrator MVM having an output terminal G suitably coupled to the gate of controlled rectifier 20 and having its input and power supply terminals C and E, respectively, connected to circuits which protect against unwanted triggering of controlled rectifier 20 in accordance with the invention as described below.
The multivibrator MVM is of a conventional design and includes transistors T81 and T82, which have collector resistors R, and R respectively, and which are interconnected by resistor R capacitor C, and resistor R4- The input circuit connected to the input terminal C of the multivibrator MVM comprises a clipping circuit SQ followed by a capacitive coupling circuit DA, to provide, in combination with the reactive network C,, R of MVM, a circuit for preventing unintentional operation of controlled rectifier 20 by transient pulses in the system.
The clipping circuit SQ includes a zener diode Z connected to positive battery terminal 21 of the vehicle and through a bias resistor R-,. A diode D, connects the point A and the anode of diode Z to ground through the vehicle breaker or points R which are connected to the battery terminal 21 by a resistor R,,.
In FIG. 2 the circuit DA, is an asymmetrical differentiator comprised of capacitor C diode D having its cathode connected to terminal C, and a resistor R, which connects the common point B between capacitor C and diode D to ground.
The circuit connected to terminal D in FIG. 2 comprises a capacitor C and resistor R,, which are parallel connected, and resistors R and R,, which connect the battery terminal 21 to the point D and the emitter of transistor TS l.
The circuit terminating at the multivibrator supply terminal E comprises an integrating circuit consisting of capacitor C, and a resistor R the latter being connected to battery terminal 21.
The output terminal G of the multivibrator is connected to the collector of transistor T82 and is connected to the silicon controlled rectifier 20 through a capacitor coupling network which, in the example shown, is also formed of an asymmetrical differentiator DA comprised of diode D capacitor C and resistors R R and R The common point F between resistors R and R is connected to the control electrode (or gate) of controlled rectifier 20..
The operation will now be described for the circuit in FIG. 2, with the aid of FIGS. 3a to 3f showing, respectively, the shape for voltages V V V V V and V at points A, B, C, D, E and F, respectively, of FIG. 2, during one operating (opening and closing) cycle of breaker R at a given rpm of the engine. In FIGS. 3a to 3f, I, is the time of opening for the contacts R and t is the time of closing of contacts R and t is the time of subsequent normal re-opening or beginning of the next cycle.
Opening of breaker contacts time When the contacts of breaker R open at time the voltage at point H changes from zero to battery voltage. At the same time, the voltage V A at the output of the clipping circuit SQ, changes from V corresponding to the forward voltage drop on diode D, with the breaker contacts R closed, to V the reverse voltage of the zener diode Z.
The voltage across zener diode Z is also applied to capacitor C and appears at point B of asymmetrical differentiator DA as an increasing voltage V This positive voltage V less the forward drop of diode D is applied to point C as voltage V which is connected to the base of the input transistor T81 of multivibrator MVM. Thus, at time I transistor T81 switches from its normal cut-off state, which it had prior to opening of contacts R, to a turn-on or conductive state. Note that at time t, the full battery voltage of terminal 21 appears at the terminal E (voltage V of FIG. 3e).
The conduction of transistor T81 causes the switching-on of normally non-conducting transistor T82 through the resistor R so that a positive pulse will appear at multivibrator output terminal G. The amplitude of this pulse depends on the battery voltage at terminal 21 and the forward voltage drop at diode D This pulse is subsequently applied to point F, after passing through differentiator DA and appears at point F and the gate of silicon controlled rectifier 20, as the voltage V of FIG. 3f causing the controlled rectifier 20 to be triggered. The triggering of controlled rectifier 20 causes discharge of capacitor 3 in FIG. 1 and hence the desired ignition.
The metastable state for the multivibrator MVM lasts for a short time, and lasts so long as the feedback control, formed by the network containing capacitor C and resistor R which may be construed as a varying current generator supplying base current to transistor T81, is sufficient to hold said multivibrator in its conductive state. During this time interval, shown in FIGS. 3a to 3f as interval t -t' capacitors C (see FIG. 3d) and C, are charged, while at point B there will be a reduction in the supply voltage provided by capacitor C (see FIG. Be).
At time 2' when the conductive state of MVM terminates and thus transistors TS! and T82 are cut off,
'voltage is removed from point G and the voltage at point C and the base of transistor T81 will see a negative voltage, the amplitude of which is initially proportional to the voltage at which capacitor C, was charged, and which decreases exponentially to zero as shown in FIG. 3c.
There will also appear a negative voltage at point B, since this point is connected through diode D to point C, with this voltage exponentially decreasing to zero in the time interval t' -t as shown in FIG. 3b.
Beginning with time the voltage at point D begins exponentially to decrease from the voltage assumed on capacitor C during the conductive state of multivibra tor MVM, to the operating voltage according to a voltage division provided by resistors R R and R while the voltage at point E, which is determined by the charging of capacitor C exponentially increases during the interval t' -t (FIG. 3e) toward the full battery voltage.
Breaker contact closing time t,
Upon closing of contacts of breaker R at time t the voltage at point H abruptly drops to zero and the voltage at point A is again the forward voltage drop on diode D1, shown as V in FIG. 3a.
This abrupt voltage change is transmitted to point B, and causes the potential of point B to change from zero at time t to a negative value which then exponentially decays to zero in the time interval t -t (FIG. 3b) due to the discharge of capacitor C This negative voltage change at B is also effective to reverse bias diode D thus increasing the time constant for the discharge of capacitor C as shown in FIG. 3c.
With the closing of breaker R, and the reduction of the voltage at point H to zero, the capacitor C discharges across R and R in the time interval t t as shown in FIG. 3d.
At time the contacts of breaker R are opened again, beginning a new cycle wherein the operation as described for cycle r 4 is repeated.
From the foregoing description the novel protective function will be apparent for the circuits connected to terminals C, D and E of the monostable multivibrator MVM.
Such circuits permit the energization for the multivibrator as a result of the opening of breaker contact R at time 1,, so that at this instant, the triggering signal for controlled rectifier 20 is available. at point G and hence at point F. At the same time, circuit operation is made independent of variations in the supply voltage. Moreover, the multivibrator cannot be made to conduct by transient pulses in the system appearing in the interval t,t which could provide improperly timed triggering of controlled rectifier 20.
Thus, unwanted signals caused by bouncing of the breaker contacts after time cannot turn on MVM since point C is at a negative potential. Note that this negative potential is highest just following contact closing when bouncing is most likely to occur.
The integrating circuit C -R connected to power supply terminal E of MVM assures the presence of a sufficient supply voltage for controlled rectifier triggering at time t independently of any fluctuations of the battery voltage about some nominal value.
At the termination of the conductive state for the monostable multivibrator MVM, the capacitor cou pling circuit connecting point G with point F assures a reverse bias for the control gate of controlled rectifier 20 to aid in its proper tum-off. From time t, this bias is developed as a result of the discharge of capacitor C which had been charged during the interval t -t' through resistors R R and R Since the coupling circuit DA is of the asymmetrical differentiator type (because of diode D,), the discharge current of capacitor C by passing through R also develops a positive voltage to reverse bias diode D Thus a triggering signal could not be issued from the monostable multivibrator output G for some time following t thereby to further insure against undesired ignition unrelated to the time of closing of points R.
The circuit of FIG. 2 provides protective circuits at all four points C, D, E and G of the multivibrator. It is apparent that in particular applications one or more of such circuits could be omitted. Moreover, the circuit could undergo modifications or changes according to specific requirements, without departing from the spirit of the invention. Moreover, the wave shapes shown in FIGS. 3a to 3f, and particularly those relating to the voltage at points B, C and D, could take a different shape, the protective function being however unchanged, particularly following time t Although this invention has been described with respect to its preferred embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in the art and, therefore, it is preferred that the invention be limited not by the specific disclosure herein but only by the appended claims.
What is claimed is:
1. In an electronic ignition control circuit for internal combustion engines; said internal combustion engines containing mechanically driven timing contact means operated between open and closed positions with a timing desired for the firing of spark plugs, and an ignition coil means; said electronic ignition control circuit including a discharge capacitor, a controlled rectifier having a pair of main terminals and a control electrode, a voltage source means, and means for charging said discharge capacitor from said voltage source means; said discharge capacitor, said pair of main terminals of said controlled rectifier and said ignition coil means being connected in series, whereby the firing of said controlled rectifier permits the discharge of said discharge capacitor into said ignition coil means; the improvement which comprises control circuit means connected to said control electrode of said controlled rectifier for firing said controlled rectifier only in response to the opening of said timing contact means; said control circuit means including a monostable multivibrator having an input circuit, and output circuit, and a power supply input circuit; first coupling circuit means for coupling said power supply input circuit to said voltage source means; second coupling circuit means including said timing contact means for coupling said input circuit to said power supply input circuit, whereby the opening of said timing contact means causes the switching of said multivibrator to a conductive state for a given relatively short period of time; and third coupling circuit means for coupling said output circuit to said control electrode of said controlled rectifier, whereby a firing signal is applied to said control electrode when said multivibrator becomes conductive; and capacitor means in said first coupling circuit means and means connecting said capacitor means to said timing contact means whereby said capacitor means charges while said timing contact means is open and is discharged when said timing contact means closes, thereby substantially to deactivate said multivibrator immediately after said timing contact means closes.
2. The circuit of claim 1 wherein said second coupling circuit means includes an asymmetric differentiating circuit.
3. The circuit of claim 1 wherein said second coupling circuit means includes a clipping circuit constituted by a zener diode connected in parallel with said timing contact means.
4. The circuit of claim 2 wherein said second coupling circuit means includes a clipping circuit constituted by a zener diode connected in parallel with said timing contact means.
5. The circuit of claim 1 wherein said multivibrator includes an input transistor means; and circuit means including a capacitor coupling said output circuit to the base electrode of said input transistor means for positively cutting off said multivibrator following the conduction thereof in response to the opening of said timing contact means.
6. The circuit of claim 1 wherein said third coupling circuit means includes capacitive coupling means.
7. The circuit of claim 6 wherein said capacitive coupling means comprises an asymmetric differentiator circuit.