CA1078915A - Capacitor discharge ignition method and system - Google Patents
Capacitor discharge ignition method and systemInfo
- Publication number
- CA1078915A CA1078915A CA237,326A CA237326A CA1078915A CA 1078915 A CA1078915 A CA 1078915A CA 237326 A CA237326 A CA 237326A CA 1078915 A CA1078915 A CA 1078915A
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- scr
- circuit
- coil
- cathode
- capacitor discharge
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02P—IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES
- F02P1/00—Installations having electric ignition energy generated by magneto- or dynamo- electric generators without subsequent storage
- F02P1/08—Layout of circuits
- F02P1/086—Layout of circuits for generating sparks by discharging a capacitor into a coil circuit
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Ignition Installations For Internal Combustion Engines (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A capacitor discharge ignition system employs charge and shut-off coils disposed about a common magnetic core. Shut-off may be a-chieved by selecting grounding an end of the trigger coil or the shut-off coil into the circuit which achieves the additional effect of loading the charge coil to protect the ignition capacitor. One circuit embodiment provides force commutation of the electronic switch, compensation for variations in temperature, inhibition of extraneous triggering of the electronic swithch and selective system shut-off. Extraneous triggering may be inhibited by the biasing of the electronic switch as a function of the polarity of the waveforms as well as by the damping of the transient which occurs at the end of the charge of the ignition capacitor. Gate protection for the electronic switch is provided by the clamping of the cathode to gate potential.
A capacitor discharge ignition system employs charge and shut-off coils disposed about a common magnetic core. Shut-off may be a-chieved by selecting grounding an end of the trigger coil or the shut-off coil into the circuit which achieves the additional effect of loading the charge coil to protect the ignition capacitor. One circuit embodiment provides force commutation of the electronic switch, compensation for variations in temperature, inhibition of extraneous triggering of the electronic swithch and selective system shut-off. Extraneous triggering may be inhibited by the biasing of the electronic switch as a function of the polarity of the waveforms as well as by the damping of the transient which occurs at the end of the charge of the ignition capacitor. Gate protection for the electronic switch is provided by the clamping of the cathode to gate potential.
Description
BACKGROUND OF THE INVENTION
The present invention is directed to a capacitor discharge ignition circuit for an internal combustion engine and more particularly to a capacitor discharge ignition circuit in which all of the operative coils are wound on the same magnetic core.
Capacitor discharge ignition circuits are well known.
Such circuits generally include a charging coil in which is generated the current utilized to charge a storage capacitor and a trigger coil utilized to generate the current necessary to effect operation of an electronic switch in the discharge circuit of the capacitor. The discharge circuit of the capa-citor includes the primary winding of a high voltage transformer so that the operation of the electronic switch to discharge the capacitor through the primary winding provides ionization potential across the air gap of an ignition device such as a spark plug for an internal combustion engine.
SU~-~RY OF THE INVENTION
The present invention provides a capacitor discharge ignition circuit comprising:-an ignition capacitor;
a charge coil for charging said capacitor;
a high voltage transformer;
an SCR for discharging said capacitor through said high voltage transformer;
a trigger coil for providing a trigger coil waveform;
a selectively operable shut-off coil positively induc-tively coupled to said trigger coil to inhibit generation of the trigger coil waveform; and, circuit means including means for gating said SCR in response to a discharge inducing compon nt of the trigger coil waveform and for force commuta-ting said SCR by applving the trigger coil 1(~78915 waveform to the SCR to induce a reverse anode-to-cathode bias.
The "shut-off" coil is selectively switched into the ignition circuit when it is desired to terminate the operation of the engine. Such a shut-off coil is described in U.S. Patent No. 3,894,524 issued July 15, 1975 assigned to the assignee o~
this invention. ;
It is known in such capacitor discharge ignition circuits that the charging coil and trigger coil may be wound on the same magnetic core whereby the timing of the charging and dis-charging of the ignition capacitor may be controlled. In accordance with another feature of the invention r the charge, trigger and shut-off coils are wound in the same direction on a common core. Three separate coils may be wound on the core or one or two separate coils may be wound intermediate taps to separate the charging and control functions to effect a substan-tial reduction in the size and expense of the circuit as well as a minimization of the assemblying process.
These and further features of the present invention will become apparent to one skilled in the art to which the invention pertains from a perusal of the following detailed description when read in con~unction with the appended drawings.
THE DRAWINGS
Figure 1 is a schematic circuit diagram of the circuit of the present invention illustrating certain current paths;
Figure 2(a) and 2(b) are illustrations of the waveforms generated by the charge coil and trigger coil of the present invention;
Figure 3(a) through (f) are illustrations of waveforms generated at various points in the circuit of the present invention; and, .
Figure 4 is a schematic circuit diagram of a second embodiment of a triggering and shut-off subcircuit which may be employed in the circuit illustrated in Figure 1.
Figure 5 is a schematic circuit diagram illustrating a third embodiment of the present invention; and, Figure 6 is a timing diagram for the waveforms generated in the circuit of Figure 5.
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~ -3-DETAILED DESCRIPTION
To facilitate an understanding of the circuit of the present invention reference may be had to the following detailed --description of the circuit of a first embodiment of the present invention shown in figures 1 and 4 and the circuit of a second r embodiment of the present invention shown in figure 5. The operation of each of the circuits in performing its various functions may be found following the description of the respec-tive circuits.
10The Circuit of the First Embodiment of the Present Invention Referring first to Figure 1 ~ere a capacitor discharge ignition circuit is illustrated as including a charge coil 10 formed, for example, of 2,500 turns of No. 36 wire and connected in a circuit including a diode 12, an ignition capacitor 14, and the primary winding 18 of a high voltage transformer 20.
Rotation of a flywheel magnet of the engine (not shown) into and out of flux cutting proximity to the charge coil 10 operates in the conventional manner to induce a voltage in the coil 10 having a waveform as generally depicted in Figure 2(a).
As illustrated in Figure 2(a), the charge coil waveform may comprise a relatively small positive portion 50, a larger negative portion 52, a large positive portion 54, and a rela-tively small negative portion 56. The current generated responsively to the voltage of the positive portions of the wave-form illustrated in Figure 2(a) will be passed through the diode 12 to effect charging of the capacitor 14 to ignition potential.
The path of conventional current associated with the above-mentioned charging of the capacitor 14 is denoted by the letter "A" in Figure 1. The diode 12 will block the passing of the current induced by the voltage of the negative portions of the charge coil waveform illustrated in Figure 2(a~.
10i8915 With continued reference to Figure 1, the ignition capa-citor 14 is connected in a discharge circuit including the primary winding 18 of the transformer 20 and an electronic switch such as the illustrated SCR 16. It should be understood, however, that any switch capable of being electronically trig-gered may be substituted therefor with appropriate changes in the polarities of the several biasing diodes associated with the switch and appropriate changes in the polarities of wave-forms applied to the switch. In the case of the SCR 16, it may be triggered into conduction by the application of a positive gate-to-cathode potential at any time that the SCR has a positive anode-to-cathode bias.
When triggered into conduction, the SCR 16 will effect the discharge of the capacitor 14 through the primary winding 18 of the transformer 20 as illustrated in Figure 1 by a current path denoted by the letter "B". The primary winding 18 of transformer 20 may comprise 100 turns of No. 26 wire and the secondary win- --ding 22 of the transformer 20 may comprise 7,000 turns of No. 44 wire. It will be apparent that the discharge of capacitor 14 through primary winding 18 will be inductively coupled by the secondary winding 22 of transformer 20 to a conventional ioniz-ation discharge device such as spark plug 24. The potential -developed across the secondary winding 22 may serve as a gap ionizing potential applied to spark plug 24 for engine ignition.
Current resulting from firing the spark plug 24 may flow as indicated by current path "C" with the particular direction of flow depending on the orientation of secondary winding 22 with respect to primary winding 18. The discharge of capacitor 14 may serve to temporarily store energy in the magnetic field established in transformer 20 by current passage through the primary winding 18. As that magnetic field collapses upon ~ .
1()7891S
. ., the cessation of current, a current path denoted by the letter "D" in Figure 1 may be established through a diode 26 and the capacitor 14 to effect a partial recharging of the capacitor 14 and, at the same time, causing the spark plug 24 to arc in the reverse direction. With the trigger potential remaining on the SCR gate electrode, the SCR 16 will again be triggered into conduction to once more effect the discharge of the capacitor 14 through the primary winding 18 of transformer 20 to again reverse the polarity of the arc of the spark plug 24. This process will continue in the presence of a triggering potential until the charge on capacitor 14 has been dissipated and has been found to produce about four or five closely spaced arcs.
The charging sequence of the circuit of the present inven-tion is illustrated graphically in the timing diagram of Figure 3. Figures 3(a) and 4(b) depict the charging coil and trigger coil waveforms discussed below in connection with Figure 2.
Figures 3(c) through 3(f) depict voltage waveforms measured at ~ -various points in the circuit with Figure 3(c) illustrating the voltage appearing across the capacitor 14. At the point on the waveform designated "80", a initial discharging of the capacitor has been induced by the negative swing in the trigger coil waveform. Voltage oscillations 82 represent the "ringing"
induced in the circuit by the repeated sequential chargings and dischargings of the capacitor 14.
Referring once again to Figure 1, a control coil 30 m~y be coaxially wound with the charge coil 10 may be tapped to provide a trigger coil 31 and shut-off coil 32 alternatively the coils may be wound separately on the core and the start end of the shut off coils connected to the finish end of the trigger coil.
The trigger coil 31 may be formed of 100 turns of No. 36 wire and the shut-off coil formed of 200 turns of No. 36 wire.
. ,_ ~ 6-Voltages may be induced in coils 31 and 32 by the passage of the flywheel magnet (not shown) into and out of flux cutting prox-imity with the control coil 30. The windings of the coils 10 and 30 are so oriented that the open eircuit output waveform of trigger coil 31 and the waveform of charge coil 10 are substan-tially in phase with one another. The phase relationship of the trigger coil and charge coil waveforms is depicted in Figure 2, wherein the output waveform of the trigger coil 31 measured from the center tap to ground appears as is illustrated -in Figure 2(b). From a comparison of Figure 2(a) with Figure
The present invention is directed to a capacitor discharge ignition circuit for an internal combustion engine and more particularly to a capacitor discharge ignition circuit in which all of the operative coils are wound on the same magnetic core.
Capacitor discharge ignition circuits are well known.
Such circuits generally include a charging coil in which is generated the current utilized to charge a storage capacitor and a trigger coil utilized to generate the current necessary to effect operation of an electronic switch in the discharge circuit of the capacitor. The discharge circuit of the capa-citor includes the primary winding of a high voltage transformer so that the operation of the electronic switch to discharge the capacitor through the primary winding provides ionization potential across the air gap of an ignition device such as a spark plug for an internal combustion engine.
SU~-~RY OF THE INVENTION
The present invention provides a capacitor discharge ignition circuit comprising:-an ignition capacitor;
a charge coil for charging said capacitor;
a high voltage transformer;
an SCR for discharging said capacitor through said high voltage transformer;
a trigger coil for providing a trigger coil waveform;
a selectively operable shut-off coil positively induc-tively coupled to said trigger coil to inhibit generation of the trigger coil waveform; and, circuit means including means for gating said SCR in response to a discharge inducing compon nt of the trigger coil waveform and for force commuta-ting said SCR by applving the trigger coil 1(~78915 waveform to the SCR to induce a reverse anode-to-cathode bias.
The "shut-off" coil is selectively switched into the ignition circuit when it is desired to terminate the operation of the engine. Such a shut-off coil is described in U.S. Patent No. 3,894,524 issued July 15, 1975 assigned to the assignee o~
this invention. ;
It is known in such capacitor discharge ignition circuits that the charging coil and trigger coil may be wound on the same magnetic core whereby the timing of the charging and dis-charging of the ignition capacitor may be controlled. In accordance with another feature of the invention r the charge, trigger and shut-off coils are wound in the same direction on a common core. Three separate coils may be wound on the core or one or two separate coils may be wound intermediate taps to separate the charging and control functions to effect a substan-tial reduction in the size and expense of the circuit as well as a minimization of the assemblying process.
These and further features of the present invention will become apparent to one skilled in the art to which the invention pertains from a perusal of the following detailed description when read in con~unction with the appended drawings.
THE DRAWINGS
Figure 1 is a schematic circuit diagram of the circuit of the present invention illustrating certain current paths;
Figure 2(a) and 2(b) are illustrations of the waveforms generated by the charge coil and trigger coil of the present invention;
Figure 3(a) through (f) are illustrations of waveforms generated at various points in the circuit of the present invention; and, .
Figure 4 is a schematic circuit diagram of a second embodiment of a triggering and shut-off subcircuit which may be employed in the circuit illustrated in Figure 1.
Figure 5 is a schematic circuit diagram illustrating a third embodiment of the present invention; and, Figure 6 is a timing diagram for the waveforms generated in the circuit of Figure 5.
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~ -3-DETAILED DESCRIPTION
To facilitate an understanding of the circuit of the present invention reference may be had to the following detailed --description of the circuit of a first embodiment of the present invention shown in figures 1 and 4 and the circuit of a second r embodiment of the present invention shown in figure 5. The operation of each of the circuits in performing its various functions may be found following the description of the respec-tive circuits.
10The Circuit of the First Embodiment of the Present Invention Referring first to Figure 1 ~ere a capacitor discharge ignition circuit is illustrated as including a charge coil 10 formed, for example, of 2,500 turns of No. 36 wire and connected in a circuit including a diode 12, an ignition capacitor 14, and the primary winding 18 of a high voltage transformer 20.
Rotation of a flywheel magnet of the engine (not shown) into and out of flux cutting proximity to the charge coil 10 operates in the conventional manner to induce a voltage in the coil 10 having a waveform as generally depicted in Figure 2(a).
As illustrated in Figure 2(a), the charge coil waveform may comprise a relatively small positive portion 50, a larger negative portion 52, a large positive portion 54, and a rela-tively small negative portion 56. The current generated responsively to the voltage of the positive portions of the wave-form illustrated in Figure 2(a) will be passed through the diode 12 to effect charging of the capacitor 14 to ignition potential.
The path of conventional current associated with the above-mentioned charging of the capacitor 14 is denoted by the letter "A" in Figure 1. The diode 12 will block the passing of the current induced by the voltage of the negative portions of the charge coil waveform illustrated in Figure 2(a~.
10i8915 With continued reference to Figure 1, the ignition capa-citor 14 is connected in a discharge circuit including the primary winding 18 of the transformer 20 and an electronic switch such as the illustrated SCR 16. It should be understood, however, that any switch capable of being electronically trig-gered may be substituted therefor with appropriate changes in the polarities of the several biasing diodes associated with the switch and appropriate changes in the polarities of wave-forms applied to the switch. In the case of the SCR 16, it may be triggered into conduction by the application of a positive gate-to-cathode potential at any time that the SCR has a positive anode-to-cathode bias.
When triggered into conduction, the SCR 16 will effect the discharge of the capacitor 14 through the primary winding 18 of the transformer 20 as illustrated in Figure 1 by a current path denoted by the letter "B". The primary winding 18 of transformer 20 may comprise 100 turns of No. 26 wire and the secondary win- --ding 22 of the transformer 20 may comprise 7,000 turns of No. 44 wire. It will be apparent that the discharge of capacitor 14 through primary winding 18 will be inductively coupled by the secondary winding 22 of transformer 20 to a conventional ioniz-ation discharge device such as spark plug 24. The potential -developed across the secondary winding 22 may serve as a gap ionizing potential applied to spark plug 24 for engine ignition.
Current resulting from firing the spark plug 24 may flow as indicated by current path "C" with the particular direction of flow depending on the orientation of secondary winding 22 with respect to primary winding 18. The discharge of capacitor 14 may serve to temporarily store energy in the magnetic field established in transformer 20 by current passage through the primary winding 18. As that magnetic field collapses upon ~ .
1()7891S
. ., the cessation of current, a current path denoted by the letter "D" in Figure 1 may be established through a diode 26 and the capacitor 14 to effect a partial recharging of the capacitor 14 and, at the same time, causing the spark plug 24 to arc in the reverse direction. With the trigger potential remaining on the SCR gate electrode, the SCR 16 will again be triggered into conduction to once more effect the discharge of the capacitor 14 through the primary winding 18 of transformer 20 to again reverse the polarity of the arc of the spark plug 24. This process will continue in the presence of a triggering potential until the charge on capacitor 14 has been dissipated and has been found to produce about four or five closely spaced arcs.
The charging sequence of the circuit of the present inven-tion is illustrated graphically in the timing diagram of Figure 3. Figures 3(a) and 4(b) depict the charging coil and trigger coil waveforms discussed below in connection with Figure 2.
Figures 3(c) through 3(f) depict voltage waveforms measured at ~ -various points in the circuit with Figure 3(c) illustrating the voltage appearing across the capacitor 14. At the point on the waveform designated "80", a initial discharging of the capacitor has been induced by the negative swing in the trigger coil waveform. Voltage oscillations 82 represent the "ringing"
induced in the circuit by the repeated sequential chargings and dischargings of the capacitor 14.
Referring once again to Figure 1, a control coil 30 m~y be coaxially wound with the charge coil 10 may be tapped to provide a trigger coil 31 and shut-off coil 32 alternatively the coils may be wound separately on the core and the start end of the shut off coils connected to the finish end of the trigger coil.
The trigger coil 31 may be formed of 100 turns of No. 36 wire and the shut-off coil formed of 200 turns of No. 36 wire.
. ,_ ~ 6-Voltages may be induced in coils 31 and 32 by the passage of the flywheel magnet (not shown) into and out of flux cutting prox-imity with the control coil 30. The windings of the coils 10 and 30 are so oriented that the open eircuit output waveform of trigger coil 31 and the waveform of charge coil 10 are substan-tially in phase with one another. The phase relationship of the trigger coil and charge coil waveforms is depicted in Figure 2, wherein the output waveform of the trigger coil 31 measured from the center tap to ground appears as is illustrated -in Figure 2(b). From a comparison of Figure 2(a) with Figure
2(b) it may be observed that the voltage waveforms are substan-tially identical in shape and differ only in amplitude as a funetion of the number of turns and impedanee of the coils.
The trigger coil 31 is connected to the gate electrode of `
SCR 16 by the novel circuit of the present invention. The finish end of the trigger coil 31 may be connected to the cathode of the SCR 16 by way of a resistor 34 in series with the parallel combination of a resistor 36 and a diode 38. The cathode of the SCR 16 may be connected to the gate of the SCR
16 through a resistor 40 and to ground through the parallel combination of a resistor 42 and a diode 44. The gate of the SCR 16 may be grounded by a diode 46. The finish end of the trigger coil 31 is eonneeted at the tap 33 to the start end of the shut-off coil 32 and the finish end of the trigger coil 31 may be grounded by the grounding of the finish end of the shut-off coil 32 through a conventional manually operable switch 48.
The circuit illustrated schematieally in Figure 1 employs a triggering and shut-off subeircuit comprised of the control coil 30, the resistor 34 and the conventional switch 48. For purposes of illustration, the triggering and shut-off subcircuit is depicted as being connected to the remaining circuitry by junctions 47 and 49.
Referring now to Figure 4, a schematic circuit diagram of a second embodiment of the triggering and shut-off subcircuit of the present invention is illustrated. The subcircuit of Figure 4 may be attached to Figure 1 by electrically connecting junctions 60 and 62 of the circuit of Figure 4 with junctions 47 and 49, respectively, of the circuit of Figure 1.
Again referring to Figure 4, the junction 60 may be con-nected to a resistor 64 and the cathode of a diode 66. The junction 60 may be selectively grounded by a conventional, manually operable switch 68. The anode of the diode 66 may be connected to the finish end of a shut-off coil 70. Advanta-geously, the shut-off coil may be formed of 100 turns of ~30 wire. Resistor 64 may be connected to the finish end of a trigger coil 72. Advantageously, the trigger coil may be formed of 100 turns of #30 wire. The start ends of the coils 70 and 72 may be grounded by connection to junction 62. Voltages may be induced in the coils 70 and 72 by the passage of the flywheel magnet (not shown) into and out of flux cutting proximity with the coils. Coils 70 and 72 may be so oriented with respect to one another and to charging coil 10 of Figure 1, that the out-put waveforms with respect to ground of all three coils are substantially in phase. This effect may be achieved by winding the coils 70, 72 and 10 on the same core so that the coils are positively inductively coupled.
With reference again to Figure 1, a gating current path denoted by the letter "E" is established for the negative por-tion of the trigger coil waveform induced from ground potential (i.e., the start end of the coil 31 or coil 72 of Figure 4) through the diode 46, the resistor 40, the diode 38, the junction 47 and the triggering and shut-off subcircuit. It will be apparent that when a negative voltage with respect to 1~)7~915 ground is induced at the junction 47, the cathode of the SCR 16 will be held negative with respect to the gate due to conduction of the diode 46 whereby the gating of the SCR 16 may be effected.
Figure 3(d) illustrates the cathode-to-gate voltage which reaches the minimum value necessary to trigger the SCR 16 into conduction at the point 84 on the waveform. The positive going spikes 86 in the waveform of Figure 3(d) reflect the repeated swamping of the cathode potential imposed by the trigger coil waveform due to a positive forward voltage developed across the diode 44 when current flows along path "B".
With reference once more to Figure 1, the negative compon-ent of the trigger coil waveform may tend to establish a flow of conventional current along the path designated by the letter "F". As will hereinafter appear, this current flow tends to force commutate the SCR 16. -When a positive voltage with respect to ground is induced at the junction 47 during the positive portion of the induced waveform of Figure 2(b) it will be apparent that the resistors 36 and 42 act as a voltage divider which will impose a positive voltage on the cathode of the SCR 16 to prevent the conduction thereof. The current path so established is denoted by the letter "G" in Figure 1.
Force Commutation It is important that conduction of the SCR 16 be inter-rupted after firing since the current normally utilized to charge the capacitor 14 will otherwise be shunted to ground through the SCR 16 and the diode 44. A negative cathode-to-gate voltage on the SCR applied at the junction 47 by the trigger coil will serve to gate the SCR 16 into conduction and to develop a voltage drop across the diode 44 due to the forward resistance thereof. The voltage drop developed across diode 44 raises the voltage at the cathode of the SCR 16 and swamps the negative gating voltage provided by trigger coil 31. As a result, the conduction of the SCR 16 immediately serves to back bias the diode 46 out of conduction and to thereby remove the negative cathode-to-gate bias until the capacitor is dis-charged. The relationship between the capacitor voltage and the cathode-to-gate voltage is illustrated in Figures 3(c) and
The trigger coil 31 is connected to the gate electrode of `
SCR 16 by the novel circuit of the present invention. The finish end of the trigger coil 31 may be connected to the cathode of the SCR 16 by way of a resistor 34 in series with the parallel combination of a resistor 36 and a diode 38. The cathode of the SCR 16 may be connected to the gate of the SCR
16 through a resistor 40 and to ground through the parallel combination of a resistor 42 and a diode 44. The gate of the SCR 16 may be grounded by a diode 46. The finish end of the trigger coil 31 is eonneeted at the tap 33 to the start end of the shut-off coil 32 and the finish end of the trigger coil 31 may be grounded by the grounding of the finish end of the shut-off coil 32 through a conventional manually operable switch 48.
The circuit illustrated schematieally in Figure 1 employs a triggering and shut-off subeircuit comprised of the control coil 30, the resistor 34 and the conventional switch 48. For purposes of illustration, the triggering and shut-off subcircuit is depicted as being connected to the remaining circuitry by junctions 47 and 49.
Referring now to Figure 4, a schematic circuit diagram of a second embodiment of the triggering and shut-off subcircuit of the present invention is illustrated. The subcircuit of Figure 4 may be attached to Figure 1 by electrically connecting junctions 60 and 62 of the circuit of Figure 4 with junctions 47 and 49, respectively, of the circuit of Figure 1.
Again referring to Figure 4, the junction 60 may be con-nected to a resistor 64 and the cathode of a diode 66. The junction 60 may be selectively grounded by a conventional, manually operable switch 68. The anode of the diode 66 may be connected to the finish end of a shut-off coil 70. Advanta-geously, the shut-off coil may be formed of 100 turns of ~30 wire. Resistor 64 may be connected to the finish end of a trigger coil 72. Advantageously, the trigger coil may be formed of 100 turns of #30 wire. The start ends of the coils 70 and 72 may be grounded by connection to junction 62. Voltages may be induced in the coils 70 and 72 by the passage of the flywheel magnet (not shown) into and out of flux cutting proximity with the coils. Coils 70 and 72 may be so oriented with respect to one another and to charging coil 10 of Figure 1, that the out-put waveforms with respect to ground of all three coils are substantially in phase. This effect may be achieved by winding the coils 70, 72 and 10 on the same core so that the coils are positively inductively coupled.
With reference again to Figure 1, a gating current path denoted by the letter "E" is established for the negative por-tion of the trigger coil waveform induced from ground potential (i.e., the start end of the coil 31 or coil 72 of Figure 4) through the diode 46, the resistor 40, the diode 38, the junction 47 and the triggering and shut-off subcircuit. It will be apparent that when a negative voltage with respect to 1~)7~915 ground is induced at the junction 47, the cathode of the SCR 16 will be held negative with respect to the gate due to conduction of the diode 46 whereby the gating of the SCR 16 may be effected.
Figure 3(d) illustrates the cathode-to-gate voltage which reaches the minimum value necessary to trigger the SCR 16 into conduction at the point 84 on the waveform. The positive going spikes 86 in the waveform of Figure 3(d) reflect the repeated swamping of the cathode potential imposed by the trigger coil waveform due to a positive forward voltage developed across the diode 44 when current flows along path "B".
With reference once more to Figure 1, the negative compon-ent of the trigger coil waveform may tend to establish a flow of conventional current along the path designated by the letter "F". As will hereinafter appear, this current flow tends to force commutate the SCR 16. -When a positive voltage with respect to ground is induced at the junction 47 during the positive portion of the induced waveform of Figure 2(b) it will be apparent that the resistors 36 and 42 act as a voltage divider which will impose a positive voltage on the cathode of the SCR 16 to prevent the conduction thereof. The current path so established is denoted by the letter "G" in Figure 1.
Force Commutation It is important that conduction of the SCR 16 be inter-rupted after firing since the current normally utilized to charge the capacitor 14 will otherwise be shunted to ground through the SCR 16 and the diode 44. A negative cathode-to-gate voltage on the SCR applied at the junction 47 by the trigger coil will serve to gate the SCR 16 into conduction and to develop a voltage drop across the diode 44 due to the forward resistance thereof. The voltage drop developed across diode 44 raises the voltage at the cathode of the SCR 16 and swamps the negative gating voltage provided by trigger coil 31. As a result, the conduction of the SCR 16 immediately serves to back bias the diode 46 out of conduction and to thereby remove the negative cathode-to-gate bias until the capacitor is dis-charged. The relationship between the capacitor voltage and the cathode-to-gate voltage is illustrated in Figures 3(c) and
3(d).
When the charge on the capacitor 14 is reduced below that value which effects back biasing of the diode 46, a negative cathode-to-gate potential may again be imposed by the negative component of the trigger coil waveform. The SCR may remain conductive permitting current flow along the conventional -current path denoted by the letter "F". This latter current -path pulls the SCR anode negative and reverses the charge on the ignition capacitor. This removes the positive anode-to-cathode SCR bias and force commutates the SCR out of conduction.
The effects on the anode potential due to the current flow along path "F" are illustrated in Figure 3(e) by the small negative voltage 88 appearing at the anode after discharge of the capacitor. This small negative voltage may operate to place a slight reverse charge on the capacitor.
Gate Bias Protection The continued presence of the negative voltage component of the trigger coil on the SCR cathode after discharge of the capacitor may not produce an excessive gate-to-cathode current in the circuit of the present invention. The SCR gate voltage is the voltage drop across the diode 46 and the SCR cathode voltage is the drop across the diode 26 and the SCR anode-to-cathode junction. The maximum forward voltage which may appear ,.,, --10--, .
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across the diodes 46 and 26 will be nearly the same and will inany event, be limited to approximately 1 volt depending on the composition of the semi-conductor material out of which the diodes are constructed. Thus the maximum gate-to-cathode potential is limited, approximately to the forward voltage across the SCR from anode-to-cathode. This voltage drop will be insufficient to damage the SCR when applied gate-to-cathode.
Circuit Temperature Stability It is known in the art that both the triggering requirements of an SCR and the anode-to-cathode holding current are dependent on the temperature of the device junctions. It is desirable to compensate for these temperature variations to provide ignition ;~
sparks of uniform timing and duration through a broad range of ambient temperatures.
The biasing and interconnection of SCR 16 and diode 44 in the present invention may provide improved circuit stability over wide variation in ambient temperature. The forward resis-tance across diode 44 remains relatively stable as temperature incraases when compared to the forward resistance of the SCR 16.
The amount of current flowing through the series combination of the SCR 16 and the diode 44 will depend on the sum of the for-ward resistances presented by the devices. The thermal stability of the forward resistance of diode 44 renders the series resistance of the combination more stable. As a result the ~-voltage required to maintain the holding current through the SCR tends to remain constant.
Temperature compensation of the gate signal to SCR 16 may be obtained by the selection of trigger circuit parameters to cause the impedance of the trigger signal source, i.e., trigger coil 31, resistor 34 and resistor 42, to increase with 1078g1S
increasing temperature and thereby reduce the gate current in accordance with the reduced gate current requir~ment of SCR 16 with increasing temperature. Hence, the conduction of the SCR can be made quite stable over a wide range of temper-ature changes.
The temperature stability of the circuit is also greatly enhanced by the gate-to-cathode resistor 40. The selection of the value of the resistance of the external resistor 40 several orders of magnitude below that of the internal resistance of the SCR insures that most of the current will flow through the resistor 40. The impedance of the external resistor 40 is relatively constant with respect to changes in temperature while the internal impedance of the SCR changes nonlinearly with variations in temperature.
Gate Sensitivity With continued reference to Figure 1, the trigger coil waveform and the circuit connecting the coil to the gate and cathode of SCR 16 are operative to inhibit triggering of the SCR 16 during the charging of the capacitor 14. This is a desirable result, since triggering of the SCR 16 during capa- ;
citor charging could prevent proper charging of the capacitor ;~
14 and could discharge the gap ionization device 24 at an incorrect time in a combustion cycle of the engine for which the circuit provides an ignition spark.
With reference also to Figure 2 as previously noted, the positive voltage component 54 of the charge coil waveform de-picted in Figure 2(a) is applied to the capacitor 14 through the diode 12. A positive waveform component 60 of the trigger coil waveform depicted in Figure 2(b) appears at the tap 33 substantially in phase with positive charging component 54 of `~.
:1~)7891S
the charge coil waveform. This positive waveform component 54 of the trigger coil waveform results in a current along the current path denoted by the letter "G" in Figure 1. Due to the forward resistance of the diode 44, this current flow tends to hold the cathode of the SCR 16 at a positive voltage with respect to ground. Since no current flows through the back biased diode 46, the gate and cathode of the SCR are held at essentially the same positive voltage by the absence of current through the resistor 40. The value of the current along path "G" and the degree of back bias of the diode 46 is controll-able by the selection of the value of the resistor 36. The resistor 36 also suppresses the end of charging current tran-sient and substantially diminishes the undesired triggering of the SCR.
Referring to Figure 3, the cathode-to-gate voltage wave-form is illustrated for the circuit of the present invention in Figure 3(d). Figure 3(f) illustrates the cathode-to-gate waveform for the circuit of the present invention where the resistor 36 has been eliminated. A transient spike, denoted by the numeral 90, is caused by back emf occurring at the end of charging of the capacitor 14. The transient spike 90 may ~-be sufficient to cause extraneous triggering at an incorrect time in the combustion cycle of the engine. As may be noted with reference to Figure 3(d), the back emf transient is completely damped out in the circuit of the present invention incorporating the resistor 36.
Referring once more to Figure 2(b), it may be noted that the positive waveform component 60 of the trigger coil depicted in Figure 2(b) is preceded by the negative waveform component 58 of the trigger coil waveform. As discussed above, triggering ` 1()7891S
of the SCR 16 induced by the appearance of negative voltage component 58 at tap 33 of the trigger coil.
Engine Shut-Off With reference to Figure 1, the operation of the circuit heretofore described has assumed a condition in which the con-tacts of the manually operable switch 48 have remained in an open condition. The closure of the contacts of switch 48 by the operator will insure engine shut-off.
As discussed above, the circuit of the present invention may include a shut-off coil 32 connected in series with the trigger coil 31 and disposed in flux cutting proximity to a fly-wheel magnet of the engine. The shut-off coil 32 may be oper-able to reduce the magnetic flux in proximity of the trigger coil 31 when the series combination of the two coils is shorted by means of the switch 48. Where the shut-off coil and trigger coil are positively inductively coupled, i.e., where the flux in the coils tend to induce current flow through both coils in the same direction the shorting of the series combination of the two coils loads the cores of the coils and inhibits generation of the trigger coil waveform. The shut-off coil and trigger coil may be positively inductively coupled by being wound in the same direction about a common core and may be separate coils or portions of the same coil as earlier described.
The shorting of the shut-off coil or the series combina-tion of the shut-off coil and trigger coil also loads the core for the charge coil and reduces the amplitude of the capacitor charging waveform. Thus, closing of the switch 48 inhibits the gating of the electronic switch 16 and, at the same time, prevent overcharging of capacitor 14 and overloading of electronic switch 16 by the loading of the core shared with the charge coil.
1~)7891s Note that embodiments of the present invention may be operative to facilitate engine shut off by the selective loading of the flux confining core of either or both the charging coil and the trigger coil. For the purposes of this application, the term "laoding" when used in conjunction with the word "core" indicates a reduction in the value of the flux induced by the rotating magnetic me~ber and confined within said core.
The reduction of flux may be of sufficient magnitude in rela- -tion to the core parameters and winding parameters of the coils to accomplish any or all of the following: prevent overcharging of the capacitor while the engine coasts to a stop; prevent sufficient charging current to be induced in the charging coil to permit firing of the gap ionization device; and prevent a sufficient triggering signal to be induced in the trigger coil to trigger the electronic switch. In the embodiment of the present invention above described, engine shut off may be achieved if the circuit selectably connecting the shut-off coil 32 to ground has a resistance in a range from zero to ten ohms. Sufficient loading may also be achieved by directly shorting trigger coil 31 to ground.
~, ~
~()789~5 ~``
With reference to Figure 4, the functioning of an alternate triggering and shut-off subcircuit will be described. Where the subcircuit of Figure 4 is connected to the gating circuitry of Figure 1 in place of the triggering and shut-off subcircuit of Figure 1, the manually operable switch 68 is in an open position during engine operation. The closure of the switch 68 by the operator will insure engine shut-off.
As discussed above, the triggering and shut-off subcircuit of Figure 4 may include the trigger coil 72 and the shut-off coil 70, connected in series and positively inductively coupled with each other and with the chargir.g coil 10. During engine operation, the negative component of the trigger coil waveform is delivered to the gating circuitry through the resistor 64.
The negative component of the shut-off coil waveform is blocked by the diode 66. The positive components of both the triggering coil and shut-off coil reinforce one another and tend to hold the cathode of the SCR 16 at a positive voltage with respect to ground, thus inhibiting undesired triggering of the SCR during the charging of the capacitor 14.
Closure of the manually operable switch 68 grounds the out-puts of both the trigger coil and the shut-off coil. Thus no negative gating pulse is applied to the cathode of the SCR and consequently, engine ignition will cease. However, subsequent charging waveforms continue to be generated by the charging coil 10 as the engine coasts to a stop. Because the trigger and shut-off coils are inductively coupled to the charging coil, the output of the charging coil is inhibited by the loading of the core shared by the coils. In this way, overcharging of capa-citor 14 is prevented.
; -16-1()78915 Independently Variable Controls A significant advantage of the present circuit is the independence of the gate sensitivity (as provided by the resistor 40), gate current (as provided by the resistor 34 or resistor 64 of the embodiment of Figure 4) and the degree of back bias controls (as provided by the resistor 36). In addition, the value of the resistor 42 independently determines the volt-age picked off the voltage divider network and thus the point in the magnetic cycle at which the threshhold voltage of the SCR
lQ is reached. Gate noise is also minimized by the resistor 42 and the stability of the SCR is improved by the ground connection established therethrough. The value of resistor 42 may be sel-ected to fix the minimum engine speed at Whichtriggering of the SCR will occur. The values of each of these components may be selectively varied to vary one circuit operating parameter with-out affecting the other operating parameters of the circuit.
Circuit Values In the exemplary circuit of Figure 1, the values of the various circuit components may be as follows:-SCR 16 G.E. No. C1106D
Resistor 34 10 ohms, 0.5 watt Resistor 36 100 ohms, 0.25 watt Resistors 40 &
42 18 ohms, 0.25 watt Capacitor 14 0.68 microfarads ~iodes 38,44 *
& 46 GI No. GlB*
Diode 26 GI No. GlH*
Diode 12 GI No. HG4 , 6v.
In the exemplary circuit of Figure 4, the values of the various circuit components may be as follows:-Resistor 64 18 ohms, 0*5 watt Diode 66 GI No. GlB
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ADVANTAGES OF THE CIRCUIT
. _ As has been explained in connection with the exemplary circuit of Figure 1, the present invention provides force com-mutation subsequent to the complete discharge of the ignition capacitor. The commutation is induced by the control signal provided by the triggering coil.
In addition, the circuit provides gate bias protection by limiting the voltage drop between the control and output electrodes of the electronic switch during the application of the triggering wave component of the control signal to the electronic switch.
Further, the circuit provides operating stability through variations in ambient temperature by the following mechanisms:
(1) connecting a thermally stable resistive element in series with the electronic switch in the output current path of the electronic switch; (2) matching thermal variations of the impedance of the control signal source with thermal variations in the triggering requirements of the electronic switch; and, (3) clamping the control electrode of the electronic switch to an output electrode of the switch by means of a resistive element with a value several orders of magnitude smaller than the control-to-output resistance of the electronic switch.
Yet a further advantage of the present invention is that it provides a parallel combination of a unidirectional impedance element and a bidirectional impedance element, which combination is operative to transmit the triggering component of the control signal to the control electrode of the electronic switch while being operative to damp triggering inducing transients in the absence of the triggering component of the control signal.
An additional advantage of the present invention is that it provides a capacitor discharge ignition circuit which may be shut down by shorting the trigger coil to ground by means of a low impedance, manually operable switch. A further advantage of this shut down function is that the shorting of the trigger coil loads a common core on which the charging coil is wound thus preventing overcharging of the ignition capacitor as the engine coasts to a stop.
Yet a further advantage of the present invention is that it provides for independent variation of gate sensitivity, gate cur-rent, engine speed and SCR back bias through a design choice of values of three discrete resistors.
THE CIRCUIT OF A SECOND EMBODIMENT
With reference to Figure 5 where a two-legged magnetic core 110 is illustrated, two coils 112 and 113 are wound about one leg thereof. The coil 113 may be easily converted into two separate coils 116 and 118 during the manufacturing process by the tapping thereof at a point intermediate the ends thereof. In Figure 5, for example, the coil 112 may comprise 2,500 turns which are utilized as a charging coil 114 for the ignition circuit subsequently to be described. One hundred turns of the coil 113 may be utilized as the trigger coil 116 for the ignition circuit, and an additional 100 turns utilized as the shut-off coil 118 for the ignition circuit.
One end of the shut-off coil 118 may be connected through a suitable conventional manually operable switch 120 to ground and the tap between the trigger coil 116 and the shut-off coil 118 connected through a diode 122 to the gate electrode of a grounded cathode of an SCR 126. The gate electrode of the SCP 126 may also be grounded through the parallel combination of a capaci~or 128 and a resistor 130.
The ungrounded end of the charging coil 114 may be connected through a diode 132 to the anode of the SCR 126 and to the series combination of the ignition capacitor 134 and the primary winding 3~
`~ 136 of the ignition transformer. A di~u-a~ is connected across the SCR 126 for commutating purposes.
` 1078915 The secondary winding 140 of the ignition transformer may be connected to the gap ignition device 142 such as a conventional spark plug of an intern~l combustion engine.
In operation, the flywheel responsive movement of a magnetic element into and out of proximity to the free ends of the core 110 will generate positive, negative and then positive impulses. The first positive impulse will be passed through the diode 132 but effects little charging of the storage capacitor 134 at speeds below about 8,000 r.p.m. The negative impulse will be blocked by the diode 132 and the second positive impulse, far larger in ampl'tude as shown in Figure 6, will effect charging of the capacitor 134.
During this same time interval as shown in Figure 6, negative, positive and then negative impulses will be generated within the trigger coil 116 followed by a smaller positive impulse effectively filtered by the capacitor 128 and resistor 130 to so effect. The negative impulses will be blocked by the diode 122 during the charging of the ignition capacitor 134 by the current generated within the charging coil 114 and the large positive impulse effects operation of the SCR 126.
As shown in Figure 6, the impulses in the trigger coil 116 -are 180 degrees out of phase with the impulses in the charging coil 114 and the next subsequent generation of a positive pulse in the trigger coil 116 after the capacitor 134 has been charged by the major positive pulse in the charging coil 114 will be pas-sed through the diode 122 to the gate electrode of the SCR 126 thereby insuring the conduction thereof. The conduction of the SCR 126 provides a discharge path for the potential of the storage capacitor 134 and this discharge current is inductively coupled through the primary winding 136 and secondary winding 140 of the high voltage transformer to supply ignition potential to the ignition device 142.
OPERATION OF THE CIRCUIT
. . . _ During the normal operation of the circuit as above described, the switch 120 will remain in an open position thereby removing the shut-off coil 118 from the ignition circuit. In the event that engine shut-off is desired, the contacts of the switch 120 may be closed so that negative and then positive going impulses will be generated in the shut-off coil 118 in synchronism with the impulses generated in the charging coil 112 as illustrated in Figure 6. The positive going impulses are larger in magnitude than the corresponding netative pulses of the trigger coil due to the resistance 124 in the trigger coil circuit. These positive impulses will be passed through the diode 122 to the gate electrode of the SCR 126 to insure the conduction thereof during the time interval in which the charging coil 114 is seeking to charge the ignition capacitor 134. The conduction of the SCR during this time -interval shunts current away from the capacitor 134 and prevents the accumulation thereon of sufficient charge to provide gas ionization potential to the ignition device 142.
Because all of the coils 114, 116 and 118 are wound on the same leg of the core 110, and because the trigger coil 116 and shut-off coil 118 induced currents are opposed in polarity, either --the number of turns in the shut-off coil 118 must be at least as great as the number of turns in the trigger coil 116 to insure the conduction of the SCR 126 during the normal capacitor 134 charging -cycle when engine shut-off is desired, or the impedance in the trigger coil circuit must be greater.
ADVANTAGES OF THE CIRCUIT
~ _ .
A significant advantage of both of the circuits as above described includes the removal of the engine shut-off means from the charging circuit. AS is frequently the case where ignition circuits such as those herein disclosed are utilized in hostile environments such as portable chain saws, sawdust and/or other debris together with moisture may provide a shunt between the leads for the charging coil, particularly where these leads are exposed for connection to a mechanical shut-off switch. As the resistance of this shunt decreases, more of the current from the charging coil will be shunted away from the ignition capacitor.
In the circuits of the present invention, the mechanical switch has been eliminated from the high voltage charging circuit and only the relatively low voltage of the relatively few turns of the shut-off coil will be subject to this shunt. Since the trigger current can be greatly reduced without inhibiting operation, and since the more critical high voltage charging coil is protected, operation of the circuit in a hostile environment is greatly enhanced.
An additional and very significant advantage is the simplicity of manufacture achieved by the present invention. A significantly less expensive circuit results as a result of both manufacturing ~; and assemblying techniques.
The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
~; - , . , . ,- .
When the charge on the capacitor 14 is reduced below that value which effects back biasing of the diode 46, a negative cathode-to-gate potential may again be imposed by the negative component of the trigger coil waveform. The SCR may remain conductive permitting current flow along the conventional -current path denoted by the letter "F". This latter current -path pulls the SCR anode negative and reverses the charge on the ignition capacitor. This removes the positive anode-to-cathode SCR bias and force commutates the SCR out of conduction.
The effects on the anode potential due to the current flow along path "F" are illustrated in Figure 3(e) by the small negative voltage 88 appearing at the anode after discharge of the capacitor. This small negative voltage may operate to place a slight reverse charge on the capacitor.
Gate Bias Protection The continued presence of the negative voltage component of the trigger coil on the SCR cathode after discharge of the capacitor may not produce an excessive gate-to-cathode current in the circuit of the present invention. The SCR gate voltage is the voltage drop across the diode 46 and the SCR cathode voltage is the drop across the diode 26 and the SCR anode-to-cathode junction. The maximum forward voltage which may appear ,.,, --10--, .
.
across the diodes 46 and 26 will be nearly the same and will inany event, be limited to approximately 1 volt depending on the composition of the semi-conductor material out of which the diodes are constructed. Thus the maximum gate-to-cathode potential is limited, approximately to the forward voltage across the SCR from anode-to-cathode. This voltage drop will be insufficient to damage the SCR when applied gate-to-cathode.
Circuit Temperature Stability It is known in the art that both the triggering requirements of an SCR and the anode-to-cathode holding current are dependent on the temperature of the device junctions. It is desirable to compensate for these temperature variations to provide ignition ;~
sparks of uniform timing and duration through a broad range of ambient temperatures.
The biasing and interconnection of SCR 16 and diode 44 in the present invention may provide improved circuit stability over wide variation in ambient temperature. The forward resis-tance across diode 44 remains relatively stable as temperature incraases when compared to the forward resistance of the SCR 16.
The amount of current flowing through the series combination of the SCR 16 and the diode 44 will depend on the sum of the for-ward resistances presented by the devices. The thermal stability of the forward resistance of diode 44 renders the series resistance of the combination more stable. As a result the ~-voltage required to maintain the holding current through the SCR tends to remain constant.
Temperature compensation of the gate signal to SCR 16 may be obtained by the selection of trigger circuit parameters to cause the impedance of the trigger signal source, i.e., trigger coil 31, resistor 34 and resistor 42, to increase with 1078g1S
increasing temperature and thereby reduce the gate current in accordance with the reduced gate current requir~ment of SCR 16 with increasing temperature. Hence, the conduction of the SCR can be made quite stable over a wide range of temper-ature changes.
The temperature stability of the circuit is also greatly enhanced by the gate-to-cathode resistor 40. The selection of the value of the resistance of the external resistor 40 several orders of magnitude below that of the internal resistance of the SCR insures that most of the current will flow through the resistor 40. The impedance of the external resistor 40 is relatively constant with respect to changes in temperature while the internal impedance of the SCR changes nonlinearly with variations in temperature.
Gate Sensitivity With continued reference to Figure 1, the trigger coil waveform and the circuit connecting the coil to the gate and cathode of SCR 16 are operative to inhibit triggering of the SCR 16 during the charging of the capacitor 14. This is a desirable result, since triggering of the SCR 16 during capa- ;
citor charging could prevent proper charging of the capacitor ;~
14 and could discharge the gap ionization device 24 at an incorrect time in a combustion cycle of the engine for which the circuit provides an ignition spark.
With reference also to Figure 2 as previously noted, the positive voltage component 54 of the charge coil waveform de-picted in Figure 2(a) is applied to the capacitor 14 through the diode 12. A positive waveform component 60 of the trigger coil waveform depicted in Figure 2(b) appears at the tap 33 substantially in phase with positive charging component 54 of `~.
:1~)7891S
the charge coil waveform. This positive waveform component 54 of the trigger coil waveform results in a current along the current path denoted by the letter "G" in Figure 1. Due to the forward resistance of the diode 44, this current flow tends to hold the cathode of the SCR 16 at a positive voltage with respect to ground. Since no current flows through the back biased diode 46, the gate and cathode of the SCR are held at essentially the same positive voltage by the absence of current through the resistor 40. The value of the current along path "G" and the degree of back bias of the diode 46 is controll-able by the selection of the value of the resistor 36. The resistor 36 also suppresses the end of charging current tran-sient and substantially diminishes the undesired triggering of the SCR.
Referring to Figure 3, the cathode-to-gate voltage wave-form is illustrated for the circuit of the present invention in Figure 3(d). Figure 3(f) illustrates the cathode-to-gate waveform for the circuit of the present invention where the resistor 36 has been eliminated. A transient spike, denoted by the numeral 90, is caused by back emf occurring at the end of charging of the capacitor 14. The transient spike 90 may ~-be sufficient to cause extraneous triggering at an incorrect time in the combustion cycle of the engine. As may be noted with reference to Figure 3(d), the back emf transient is completely damped out in the circuit of the present invention incorporating the resistor 36.
Referring once more to Figure 2(b), it may be noted that the positive waveform component 60 of the trigger coil depicted in Figure 2(b) is preceded by the negative waveform component 58 of the trigger coil waveform. As discussed above, triggering ` 1()7891S
of the SCR 16 induced by the appearance of negative voltage component 58 at tap 33 of the trigger coil.
Engine Shut-Off With reference to Figure 1, the operation of the circuit heretofore described has assumed a condition in which the con-tacts of the manually operable switch 48 have remained in an open condition. The closure of the contacts of switch 48 by the operator will insure engine shut-off.
As discussed above, the circuit of the present invention may include a shut-off coil 32 connected in series with the trigger coil 31 and disposed in flux cutting proximity to a fly-wheel magnet of the engine. The shut-off coil 32 may be oper-able to reduce the magnetic flux in proximity of the trigger coil 31 when the series combination of the two coils is shorted by means of the switch 48. Where the shut-off coil and trigger coil are positively inductively coupled, i.e., where the flux in the coils tend to induce current flow through both coils in the same direction the shorting of the series combination of the two coils loads the cores of the coils and inhibits generation of the trigger coil waveform. The shut-off coil and trigger coil may be positively inductively coupled by being wound in the same direction about a common core and may be separate coils or portions of the same coil as earlier described.
The shorting of the shut-off coil or the series combina-tion of the shut-off coil and trigger coil also loads the core for the charge coil and reduces the amplitude of the capacitor charging waveform. Thus, closing of the switch 48 inhibits the gating of the electronic switch 16 and, at the same time, prevent overcharging of capacitor 14 and overloading of electronic switch 16 by the loading of the core shared with the charge coil.
1~)7891s Note that embodiments of the present invention may be operative to facilitate engine shut off by the selective loading of the flux confining core of either or both the charging coil and the trigger coil. For the purposes of this application, the term "laoding" when used in conjunction with the word "core" indicates a reduction in the value of the flux induced by the rotating magnetic me~ber and confined within said core.
The reduction of flux may be of sufficient magnitude in rela- -tion to the core parameters and winding parameters of the coils to accomplish any or all of the following: prevent overcharging of the capacitor while the engine coasts to a stop; prevent sufficient charging current to be induced in the charging coil to permit firing of the gap ionization device; and prevent a sufficient triggering signal to be induced in the trigger coil to trigger the electronic switch. In the embodiment of the present invention above described, engine shut off may be achieved if the circuit selectably connecting the shut-off coil 32 to ground has a resistance in a range from zero to ten ohms. Sufficient loading may also be achieved by directly shorting trigger coil 31 to ground.
~, ~
~()789~5 ~``
With reference to Figure 4, the functioning of an alternate triggering and shut-off subcircuit will be described. Where the subcircuit of Figure 4 is connected to the gating circuitry of Figure 1 in place of the triggering and shut-off subcircuit of Figure 1, the manually operable switch 68 is in an open position during engine operation. The closure of the switch 68 by the operator will insure engine shut-off.
As discussed above, the triggering and shut-off subcircuit of Figure 4 may include the trigger coil 72 and the shut-off coil 70, connected in series and positively inductively coupled with each other and with the chargir.g coil 10. During engine operation, the negative component of the trigger coil waveform is delivered to the gating circuitry through the resistor 64.
The negative component of the shut-off coil waveform is blocked by the diode 66. The positive components of both the triggering coil and shut-off coil reinforce one another and tend to hold the cathode of the SCR 16 at a positive voltage with respect to ground, thus inhibiting undesired triggering of the SCR during the charging of the capacitor 14.
Closure of the manually operable switch 68 grounds the out-puts of both the trigger coil and the shut-off coil. Thus no negative gating pulse is applied to the cathode of the SCR and consequently, engine ignition will cease. However, subsequent charging waveforms continue to be generated by the charging coil 10 as the engine coasts to a stop. Because the trigger and shut-off coils are inductively coupled to the charging coil, the output of the charging coil is inhibited by the loading of the core shared by the coils. In this way, overcharging of capa-citor 14 is prevented.
; -16-1()78915 Independently Variable Controls A significant advantage of the present circuit is the independence of the gate sensitivity (as provided by the resistor 40), gate current (as provided by the resistor 34 or resistor 64 of the embodiment of Figure 4) and the degree of back bias controls (as provided by the resistor 36). In addition, the value of the resistor 42 independently determines the volt-age picked off the voltage divider network and thus the point in the magnetic cycle at which the threshhold voltage of the SCR
lQ is reached. Gate noise is also minimized by the resistor 42 and the stability of the SCR is improved by the ground connection established therethrough. The value of resistor 42 may be sel-ected to fix the minimum engine speed at Whichtriggering of the SCR will occur. The values of each of these components may be selectively varied to vary one circuit operating parameter with-out affecting the other operating parameters of the circuit.
Circuit Values In the exemplary circuit of Figure 1, the values of the various circuit components may be as follows:-SCR 16 G.E. No. C1106D
Resistor 34 10 ohms, 0.5 watt Resistor 36 100 ohms, 0.25 watt Resistors 40 &
42 18 ohms, 0.25 watt Capacitor 14 0.68 microfarads ~iodes 38,44 *
& 46 GI No. GlB*
Diode 26 GI No. GlH*
Diode 12 GI No. HG4 , 6v.
In the exemplary circuit of Figure 4, the values of the various circuit components may be as follows:-Resistor 64 18 ohms, 0*5 watt Diode 66 GI No. GlB
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ADVANTAGES OF THE CIRCUIT
. _ As has been explained in connection with the exemplary circuit of Figure 1, the present invention provides force com-mutation subsequent to the complete discharge of the ignition capacitor. The commutation is induced by the control signal provided by the triggering coil.
In addition, the circuit provides gate bias protection by limiting the voltage drop between the control and output electrodes of the electronic switch during the application of the triggering wave component of the control signal to the electronic switch.
Further, the circuit provides operating stability through variations in ambient temperature by the following mechanisms:
(1) connecting a thermally stable resistive element in series with the electronic switch in the output current path of the electronic switch; (2) matching thermal variations of the impedance of the control signal source with thermal variations in the triggering requirements of the electronic switch; and, (3) clamping the control electrode of the electronic switch to an output electrode of the switch by means of a resistive element with a value several orders of magnitude smaller than the control-to-output resistance of the electronic switch.
Yet a further advantage of the present invention is that it provides a parallel combination of a unidirectional impedance element and a bidirectional impedance element, which combination is operative to transmit the triggering component of the control signal to the control electrode of the electronic switch while being operative to damp triggering inducing transients in the absence of the triggering component of the control signal.
An additional advantage of the present invention is that it provides a capacitor discharge ignition circuit which may be shut down by shorting the trigger coil to ground by means of a low impedance, manually operable switch. A further advantage of this shut down function is that the shorting of the trigger coil loads a common core on which the charging coil is wound thus preventing overcharging of the ignition capacitor as the engine coasts to a stop.
Yet a further advantage of the present invention is that it provides for independent variation of gate sensitivity, gate cur-rent, engine speed and SCR back bias through a design choice of values of three discrete resistors.
THE CIRCUIT OF A SECOND EMBODIMENT
With reference to Figure 5 where a two-legged magnetic core 110 is illustrated, two coils 112 and 113 are wound about one leg thereof. The coil 113 may be easily converted into two separate coils 116 and 118 during the manufacturing process by the tapping thereof at a point intermediate the ends thereof. In Figure 5, for example, the coil 112 may comprise 2,500 turns which are utilized as a charging coil 114 for the ignition circuit subsequently to be described. One hundred turns of the coil 113 may be utilized as the trigger coil 116 for the ignition circuit, and an additional 100 turns utilized as the shut-off coil 118 for the ignition circuit.
One end of the shut-off coil 118 may be connected through a suitable conventional manually operable switch 120 to ground and the tap between the trigger coil 116 and the shut-off coil 118 connected through a diode 122 to the gate electrode of a grounded cathode of an SCR 126. The gate electrode of the SCP 126 may also be grounded through the parallel combination of a capaci~or 128 and a resistor 130.
The ungrounded end of the charging coil 114 may be connected through a diode 132 to the anode of the SCR 126 and to the series combination of the ignition capacitor 134 and the primary winding 3~
`~ 136 of the ignition transformer. A di~u-a~ is connected across the SCR 126 for commutating purposes.
` 1078915 The secondary winding 140 of the ignition transformer may be connected to the gap ignition device 142 such as a conventional spark plug of an intern~l combustion engine.
In operation, the flywheel responsive movement of a magnetic element into and out of proximity to the free ends of the core 110 will generate positive, negative and then positive impulses. The first positive impulse will be passed through the diode 132 but effects little charging of the storage capacitor 134 at speeds below about 8,000 r.p.m. The negative impulse will be blocked by the diode 132 and the second positive impulse, far larger in ampl'tude as shown in Figure 6, will effect charging of the capacitor 134.
During this same time interval as shown in Figure 6, negative, positive and then negative impulses will be generated within the trigger coil 116 followed by a smaller positive impulse effectively filtered by the capacitor 128 and resistor 130 to so effect. The negative impulses will be blocked by the diode 122 during the charging of the ignition capacitor 134 by the current generated within the charging coil 114 and the large positive impulse effects operation of the SCR 126.
As shown in Figure 6, the impulses in the trigger coil 116 -are 180 degrees out of phase with the impulses in the charging coil 114 and the next subsequent generation of a positive pulse in the trigger coil 116 after the capacitor 134 has been charged by the major positive pulse in the charging coil 114 will be pas-sed through the diode 122 to the gate electrode of the SCR 126 thereby insuring the conduction thereof. The conduction of the SCR 126 provides a discharge path for the potential of the storage capacitor 134 and this discharge current is inductively coupled through the primary winding 136 and secondary winding 140 of the high voltage transformer to supply ignition potential to the ignition device 142.
OPERATION OF THE CIRCUIT
. . . _ During the normal operation of the circuit as above described, the switch 120 will remain in an open position thereby removing the shut-off coil 118 from the ignition circuit. In the event that engine shut-off is desired, the contacts of the switch 120 may be closed so that negative and then positive going impulses will be generated in the shut-off coil 118 in synchronism with the impulses generated in the charging coil 112 as illustrated in Figure 6. The positive going impulses are larger in magnitude than the corresponding netative pulses of the trigger coil due to the resistance 124 in the trigger coil circuit. These positive impulses will be passed through the diode 122 to the gate electrode of the SCR 126 to insure the conduction thereof during the time interval in which the charging coil 114 is seeking to charge the ignition capacitor 134. The conduction of the SCR during this time -interval shunts current away from the capacitor 134 and prevents the accumulation thereon of sufficient charge to provide gas ionization potential to the ignition device 142.
Because all of the coils 114, 116 and 118 are wound on the same leg of the core 110, and because the trigger coil 116 and shut-off coil 118 induced currents are opposed in polarity, either --the number of turns in the shut-off coil 118 must be at least as great as the number of turns in the trigger coil 116 to insure the conduction of the SCR 126 during the normal capacitor 134 charging -cycle when engine shut-off is desired, or the impedance in the trigger coil circuit must be greater.
ADVANTAGES OF THE CIRCUIT
~ _ .
A significant advantage of both of the circuits as above described includes the removal of the engine shut-off means from the charging circuit. AS is frequently the case where ignition circuits such as those herein disclosed are utilized in hostile environments such as portable chain saws, sawdust and/or other debris together with moisture may provide a shunt between the leads for the charging coil, particularly where these leads are exposed for connection to a mechanical shut-off switch. As the resistance of this shunt decreases, more of the current from the charging coil will be shunted away from the ignition capacitor.
In the circuits of the present invention, the mechanical switch has been eliminated from the high voltage charging circuit and only the relatively low voltage of the relatively few turns of the shut-off coil will be subject to this shunt. Since the trigger current can be greatly reduced without inhibiting operation, and since the more critical high voltage charging coil is protected, operation of the circuit in a hostile environment is greatly enhanced.
An additional and very significant advantage is the simplicity of manufacture achieved by the present invention. A significantly less expensive circuit results as a result of both manufacturing ~; and assemblying techniques.
The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
~; - , . , . ,- .
Claims (26)
1. A capacitor discharge ignition circuit comprising:
an ignition capacitor;
a charge coil for charging said capacitor;
a high voltage transformer;
an SCR for discharging said capacitor through said high voltage transformer;
a trigger coil for providing a trigger coil waveform;
a selectively operable shut-off coil positively inductively coupled to said trigger coil to inhibit genera-tion of the trigger coil waveform; and, circuit means including means for gating said SCR in response to a discharge inducing component of the trigger coil waveform and for force commutating said SCR by applying the trigger coil waveform to the SCR to induce a reverse anode-to-cathode bias.
an ignition capacitor;
a charge coil for charging said capacitor;
a high voltage transformer;
an SCR for discharging said capacitor through said high voltage transformer;
a trigger coil for providing a trigger coil waveform;
a selectively operable shut-off coil positively inductively coupled to said trigger coil to inhibit genera-tion of the trigger coil waveform; and, circuit means including means for gating said SCR in response to a discharge inducing component of the trigger coil waveform and for force commutating said SCR by applying the trigger coil waveform to the SCR to induce a reverse anode-to-cathode bias.
2. The capacitor discharge ignition circuit of claim 1 wherein said charge, trigger and shut-off coils are wound in the same direction on a common core.
3. The capacitor discharge ignition circuit of claim 1 wherein said trigger and shut-off coils comprise portions of a single coil wound coaxially with said charge coil.
4. The capacitor discharge ignition circuit of claim 1 wherein said circuit means includes a gate to cathode impedance for varying the gating sensitivity of said SCR, said circuit means including a first circuit component for varying the degree of periodic back bias on said SCR, and including a second circuit component for varying the gating current of said SCR, the variation of each of said impedance and said first and second circuit components providing sub-stantially no variation in the response of the others thereof.
5. The capacitor discharge ignition circuit of claim 1 wherein said circuit means comprises:
a first resistor connecting the cathode of said SCR
to the gate thereof, said first resistor providing inde-pendent variation of the SCR triggering sensitivity dependent on the value of said first resistor, a first diode having its anode connected to the cathode of said SCR to develop a forward voltage with respect to the finish end of said trigger coil when current flows from the anode of said SCR to the cathode of said first diode, said forward voltage being sufficient to overcome a gating voltage applied to the connection between said first diode and said SCR;
a second diode having its cathode connected to the gate of said SCR and its anode connected to the start end of said trigger coil, a second resistor connected between the cathode of said SCR and the start end of said trigger coil, said second resistor providing independent variation of the gate and cathode bias of said SCR for the duration of a discharge inhibiting component of a trigger waveform dependent on the value of said second resistor, the parallel combination of a third resistor and a third diode, the anode of which third diode is connected to the cathode of said SCR, said third resistor providing suppression of extraneous voltage transients, and a fourth resistor connecting the cathode of said third diode to the finish end of said trigger coil, said fourth resistor providing independent variation of the of the gate current of the SCR dependent on the value of said fourth resistor.
a first resistor connecting the cathode of said SCR
to the gate thereof, said first resistor providing inde-pendent variation of the SCR triggering sensitivity dependent on the value of said first resistor, a first diode having its anode connected to the cathode of said SCR to develop a forward voltage with respect to the finish end of said trigger coil when current flows from the anode of said SCR to the cathode of said first diode, said forward voltage being sufficient to overcome a gating voltage applied to the connection between said first diode and said SCR;
a second diode having its cathode connected to the gate of said SCR and its anode connected to the start end of said trigger coil, a second resistor connected between the cathode of said SCR and the start end of said trigger coil, said second resistor providing independent variation of the gate and cathode bias of said SCR for the duration of a discharge inhibiting component of a trigger waveform dependent on the value of said second resistor, the parallel combination of a third resistor and a third diode, the anode of which third diode is connected to the cathode of said SCR, said third resistor providing suppression of extraneous voltage transients, and a fourth resistor connecting the cathode of said third diode to the finish end of said trigger coil, said fourth resistor providing independent variation of the of the gate current of the SCR dependent on the value of said fourth resistor.
6. The capacitor discharge ignition circuit of claim 1 wherein said circuit means includes means for protecting said SCR by limiting the voltage drop between the control and output electrodes thereof within the time interval between the substantial discharge of the capacitor and the removal of the control signal from said SCR.
7. The capacitor discharge ignition circuit of claim 6 wherein said protecting means includes diode means for limiting the voltage difference between the gate electrode of said SCR and a reference potential and between the cathode of said SCR and said reference potential.
8. The capacitor discharge ignition circuit of claim 1 wherein said circuit means includes means for inhibiting extraneous gating of said SCR by the damping of the portion of said trigger coil waveform having a conduction inducing polarity as a function of the polarity of the signal.
9. The capacitor discharge ignition circuit of claim 8 wherein said inhibiting means includes a unidirectional impedance element connected in parallel with a bidirectional impedance element.
10. The capacitor discharge ignition circuit of claim 1 wherein said circuit means includes means variable in impedance as a function of the polarity of said trigger coil waveform for selectively inhibiting the extraneous conduc-tion of said SCR.
11. The capacitor discharge ignition circuit of claim 10 wherein said inhibiting means includes a unidirectional impedance element connected in parallel with a bidirectional impedance element.
12. The capacitor discharge ignition circuit of claim 1 wherein said circuit means includes selectively operable means for loading the core of said charge coil to thereby protect said ignition capacitor and said SCR from damage due to the continued rotation of the magnetic member in the absence of the conduction of said SCR.
13. The capacitor discharge ignition circuit of claim 12 wherein said selectively operable means includes a man-ually operable switch.
14. The capacitor discharge ignition circuit of claim 12 wherein said selectively operable means includes selec-tively short circuited coil means.
15. The capacitor discharge ignition circuit of claim 14 wherein said selectively operable means includes said trigger coil.
16. The capacitor discharge ignition circuit of claim 12 wherein said selectively operable means includes a coil selectively connected in parallel with said trigger coil.
17. The capacitor discharge ignition circuit of claim 1 wherein said circuit means includes means for suppressing transients during the time interval in which said ignition capacitor is being charged, and means for selecting the minimum operating engine speed for the circuit independently of the suppression of transients.
18. The capacitor discharge ignition circuit of claim 17 wherein said means for suppressing transients includes a unidirectional impedance in a parallel circuit with a bidirectional impedance; and, wherein said operating speed selecting means includes a bidirectional impedance in series with said parallel circuit.
19. The capacitor discharge ignition circuit of claim 1 wherein said circuit means includes impedance means con-nected between the gate and cathode of said SCR for providing an external current path in parallel with the internal gate-to-cathode current path of the SCR, the value of said external impedance means being less than the value of the internal gate-to-cathode impedance of the SCR.
20. The capacitor discharge ignition circuit of claim 19 wherein the value of said impedance means is not less than an order of magnitude less than the internal gate-to-cathode impedance of said SCR.
21. The capacitor discharge ignition circuit of claim 20 wherein said impedance means is substantially nonresponsive to changes in temperature whereby the temperature stability of said SCR is improved.
22. The capacitor discharge ignition circuit of claim 1 wherein said circuit means includes a voltage divider net-work across said trigger coil with a portion of said network including a unidirectional impedance element parallel with a bidirectional impedance element.
23. The capacitor discharge ignition circuit of claim 22 wherein said circuit means further includes:
a diode connected between the gate of said SCR and ground potential;
a diode connected between the cathode of said SCR and ground potential; and, a resistor connected between said gate and said cathode.
a diode connected between the gate of said SCR and ground potential;
a diode connected between the cathode of said SCR and ground potential; and, a resistor connected between said gate and said cathode.
24. The capacitor discharge ignition circuit of claim 23 wherein the value of said resistor is significantly less than the internal gate-to-cathode impedance of said SCR.
25. The capacitor discharge ignition circuit of claim 1 wherein said circuit means includes selectively operable coil means for loading the core of said charge coil means and said trigger coil means.
26. The capacitor discharge ignition circuit of claim 1 wherein said circuit means includes means for shutting off the engine by selective short circuiting of said trigger coil.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/514,603 US3960128A (en) | 1974-10-15 | 1974-10-15 | Capacitor discharge ignition system |
| US05/615,514 US4169446A (en) | 1975-09-22 | 1975-09-22 | CDI Method and system with in phase coils |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1078915A true CA1078915A (en) | 1980-06-03 |
Family
ID=27058250
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA237,326A Expired CA1078915A (en) | 1974-10-15 | 1975-10-09 | Capacitor discharge ignition method and system |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS6046267B2 (en) |
| CA (1) | CA1078915A (en) |
| DE (1) | DE2546128C2 (en) |
| FR (1) | FR2288228A1 (en) |
| GB (1) | GB1511576A (en) |
| SE (1) | SE418102B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9518552B2 (en) | 2011-12-07 | 2016-12-13 | Andreas Stihl Ag & Co. Kg | Ignition circuit |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3484677A (en) * | 1966-03-03 | 1969-12-16 | Phelon Co Inc | Breakerless magneto ignition system |
| US3654910A (en) * | 1970-08-10 | 1972-04-11 | Systemmatics Inc | Capacitor discharge ignition circuit |
| BE791545A (en) * | 1971-11-23 | 1973-03-16 | Brunswick Corp | IGNITION SYSTEM EQUIPPED WITH IGNITION ADVANCE STABILIZATION MEANS |
| DE2242354A1 (en) * | 1972-08-29 | 1974-03-14 | Bosch Gmbh Robert | IGNITION SYSTEM FOR COMBUSTION MACHINERY |
| DE2313273A1 (en) * | 1973-03-16 | 1974-09-26 | Bosch Gmbh Robert | IGNITION SYSTEM WITH STORAGE CAPACITOR FOR COMBUSTION ENGINES |
-
1975
- 1975-10-07 GB GB4107775A patent/GB1511576A/en not_active Expired
- 1975-10-09 CA CA237,326A patent/CA1078915A/en not_active Expired
- 1975-10-14 JP JP12297675A patent/JPS6046267B2/en not_active Expired
- 1975-10-14 FR FR7531373A patent/FR2288228A1/en active Granted
- 1975-10-14 SE SE7511321A patent/SE418102B/en not_active IP Right Cessation
- 1975-10-15 DE DE19752546128 patent/DE2546128C2/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9518552B2 (en) | 2011-12-07 | 2016-12-13 | Andreas Stihl Ag & Co. Kg | Ignition circuit |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2288228A1 (en) | 1976-05-14 |
| JPS6046267B2 (en) | 1985-10-15 |
| SE418102B (en) | 1981-05-04 |
| GB1511576A (en) | 1978-05-24 |
| SE7511321L (en) | 1976-04-20 |
| DE2546128C2 (en) | 1985-07-04 |
| JPS5231238A (en) | 1977-03-09 |
| DE2546128A1 (en) | 1976-04-29 |
| FR2288228B1 (en) | 1980-01-25 |
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| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |