US3699940A - Initiation circuit for a capacitor discharge ignition system - Google Patents

Abstract

An initiation circuit for a capacitor discharge ignition system for an internal combustion engine having an ignition capacitor, a semiconductor trigger means for discharging the ignition capacitor in synchronism with the engine, an oscillator providing charging pulses for the ignition capacitor and an enabling circuit responsive to the operation of the semiconductor trigger to couple a signal to the oscillator to initiate the same with the enabling circuit including a transistor and zener diode coupled across the output of the transistor to a reference potential to prevent changes in supply potential from initiating the oscillator. A high voltage output transformer coupled to the semiconductor trigger provides a discharge path for the ignition capacitor.

Description

United States Patent 1 4 Oct. 24, 1972 Vargas [54] INITIATION CIRCUIT FOR CAPACITOR DISCHARGE IGNITION SYSTEM [72] Inventor: Robert .1. Vargas, Arlington Heights, Ill.

[73] Assignee: Motorola, Inc., Franklin Park, Ill.

[22] Filed: July 14, 1971 [21] Appl. No.2 162,580

[52] US. Cl ..123/148 E, 123/148 R [51] Int. Cl ..F02p 1/00 [58] Field of Search ..123/148 E [56] References Cited UNITED STATES PATENTS 3,566,188 2/1971 Minks ..123/148 E 3,560,833 2/1971 Oishi ..123/148 E 3,618,580 11/1971 Dogadko ..l23/148 E 3,433,208 3/1969 Dogadko ..123/148 E 3,418,988 12/1968 Lewis ..123/148 E IGNITION SWITCH ALTERNATOR 3,605,714 9/1971 Hardin 123/148 E Primary Examiner-Laurence M. Goodridge Assistant Examiner-Ronald B. Cox

Att0rney-Mueller and Aichele ABSTRACT An initiation circuit for a capacitor discharge ignition system for an internal combustion engine having an ignition capacitor, a semiconductor trigger means for discharging the ignition capacitor in synchronism with the engine, an oscillator providing charging pulses for the ignition capacitor and an enabling circuit responsive to the operation of the semiconductor trigger to couple a signal to the oscillator to initiate the same with the enabling circuit including a transistor and zener diode coupled across the output of the transistor to a reference potential to prevent changes in supply potential from initiating the oscillator. A high voltage output transformer coupled to the semiconductor trigger provides a discharge path for the ignition capacitor.

5 Claims, 1 Drawing Figure DISTRIBUTOR DISTRIBUTOR PATENTED 0m 24 I972 Inventor ROBERT J. VARGAS BY M [9m .mOkDmzmkwa ATTYS:

INITIATION CIRCUIT FOR A-CAPACITOR DISCHARGE IGNITION SYSTEM CROSS REFERENCE TO RELATED APPLICATION A related application (Ser. No. 162,579) discloses the present invention.

BACKGROUNDOF THE INVENTION Permanent magnet altemators have been proposed as power sources for enabling circuits of capacitor discharge ignition systems with resultant uneven ripples in the supply potential being applied to the ignition circuit. Consequently in two and four cylinder internal combustion engines which have been used in outboard boat motors, the saturable oscillator, or charging circuit, may be improperly activated and the ignition capacitor charged above the limit for which the discharge circuit was originally designed. This overcharging can lead to the eventual breakdown of the semiconductor controlled rectifier because of the application of high voltages. The added charging may also breakdown the dielectric material of the ignition capacitor and shorten its useful life.

With high speed engines it is necessary to have the ignition capacitor fully charged prior to ignition. Some enabling circuits have been unable to respond quickly enough to initiate the oscillator charging circuit to fully charge the ignition capacitor prior to discharge.

An additional problem results from voltage turnoff spikes of the saturable oscillator being applied to the anode of the semiconductor controlled electrode and shortening its useful life.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved initiation and capacitor discharge ignition system.

It is a further object of this invention to prevent overcharging of the ignition capacitor of an initiation and capacitor discharge ignition system.

It is yet another object of this invention to improve the response time of the charging circuit in an initiation and capacitor discharge ignition system.

It is yet a further object of this invention to prolong the useful life of the semiconductor controlled rectifier trigger means in an initiation and capacitor discharge ignition system.

It is still another object of this invention to protect the semiconductor controlled rectifier trigger means from high voltage turnoff spikes of the power transistor in an initiation and capacitor discharge ignition system.

With the closing of an ignition switch a supply potential is coupled to the power transistor, and enabling transistor and a trigger transformer of the initiation and capacitor discharge ignition system. Ignition does not controlled rectifier through the trigger transformer operate to discharge the ignition capacitor through the semiconductor controlled rectifier to the high voltage ignition transformer. The enabling transistor, being turned on with the discharge of the ignition capacitor through the semiconductor controlled rectifier, operates to actuate the saturable oscillator for recharging the ignition capacitor and preparing the circuit for another cycle. A zener diode connected across the output of the enabling transistor prevents a ripple in the supply potential from actuating the saturable oscillator, and thus prevents the ignition capacitor from being overcharged. v

A diode between the ignition capacitor and the anode of the semiconductor controlled rectifier improves the response time of the charging oscillator by isolating other components of the control circuit means of the enabling transistor from the high capacitance ignition capacitor.

A capacitor in the control circuit means of the enabling transistor and connected between the anode of the semiconductor controlled rectifier and the reference potential prevents high voltage turnoff spikes from the power transformer from shortening the useful life of the semiconductor controlled rectifier.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a circuit diagram of the initiation circuit for a capacitor discharge ignition system in accordance with this invention.

DETAILED DESCRIPTION Referring to the drawing, with the ignition switch 12 being closed, the output electrode 66 of the PNP enabling transistor 16 of the enabling circuit 21 and the emitter or common electrode 68 of the NPN power transistor 14 of the oscillating charging circuit, and the trigger transformer 18 are energized from a 12 volt wet cell battery 17, which acts as a supply potential, of the kind generally found in vehicles or used with outboard motors. The output, or emitter electrode 20 of power transistor 14 immediately conducts because of the signal applied to the base 40 through capacitor 62 and the temperature responsive element thermistor 38. The secondary winding 19 of the trigger transformer 18 produces a voltage on the order of one volt in response, for instance, to the opening of the points in the distributor for activating a semiconductor controlled rectifier 46 to which it is connected. However, no ignition pulse is applied to the ignition transformer because the ignition capacitor 24 is not initially charged when the ignition switch is closed. The ignition capacitor 24 must be charged to about 350 volts before it will operate the ignition transfonner 50.

Charging the ignition capacitor 24 is accomplished with the saturable oscillator 41. The oscillator 41 includes the power transistor 14 having its output, emitter electrode 20 connected to the grounded primary winding 27 and one termination of the secondary winding 32 of the tertiary transformer 26. Also, secondary winding 32 operates through a parallel combination of the resistor 34 and diode 36 and the temperature responsive element 38 connected to the input, base 40 of power transistor 14 and a rectifier 42 which limits the saturation voltage. The potential at the emitter electrode is fed back to the base 40 or control electrode of power transistor 14 for increasing the output current to drive the transistor 14 into saturation. The feedback through secondary winding 32, parallel combination of resistor 34 and diode 36, and temperature responsive element 38 consequently increases the signal at the base 40 and increases the potential at emitter electrode 20. Once the power transistor 14 is driven into saturation, the oscillator shuts off and capacitor 24, having been charged through secondary winding 28, is ready for discharge through the ignition circuit. The secondary winding 28 is grounded and connected in series with diode 30 to the ignition capacitor 24 and poled to conduct only for the positive half cycle with respect to reference potential 31 of the signal from the oscillator 41 to charge the ignition capacitor 24. Zener diode 56, connected to the reference'potential 31a the same as collector or common electrode 70, clamps the output or emitter voltage of the enabling transistor 16 at a lower voltage than the supply potential so a rippling supply potential generally resulting from a permanent magnet alternator will not actuate the saturable oscillator by gating on power transistor 14. Consequently overcharging of the ignition capacitor is prevented. Capacitor 24 dielectric is protected from breaking down and its useful life lengthened along with that of the semiconductor controlled rectifier 46.

Capacitor 44, a component of the control circuit of the transistor 16 of enabling circuit 21 and connected between the anode of the semiconductor controlled rectifier 46 and the reference potential 31, acts as a voltage spike suppressor filtering out the high speed turnoff voltage spikes from the secondary winding 28 when the power transistor 14 turns off. With capacitor 44 disconnected and the discharge of the capacitor 24, the anode voltage drops to approximately 0, the reference potential, and rapidly rises to approximately 12 volts, as illustrated in waveform 39, where it remains while the winding 28 becomes energized. When the oscillator 41 goes into saturation and transistor 14 turns off, a high speed turnoff voltage spike from the transistor 14 through secondary winding 28 appears atthe anode of semiconductor controlled rectifier. This spike which is the second spike shown in waveform 39 acts to shorten the life of the semiconductor controlled rectifier 46. After the turnoff of transistor 14 simultaneously with the second spike, the capacitor 24 begins to charge again to approximately 350 volts which is also shown in that waveform. Waveform 43, in contrast, displays the voltage at the anode with capacitor 44 in circuit and the second spike, or turnoff voltage, suppressed. The use of the spike suppressor capacitor 44 has greatly enhanced the useful life of the semiconductor controlled rectifier on the order of 350 hours.

The trigger transformer 18 as heretofore mentioned is periodically energized in timed relation to the engine speed by pulses from the distributor which may function in either breaker point operation or timing sensor operation as is well-known in the art. When triggered, the semiconductor controlled rectifier 46 discharges capacitor 24 through diode 45 to the primary winding 48 of the high voltage ignition transformer 50.

With each pulse from the trigger transformer 18 the semiconductor controlled rectifier 46 is turned on permitting the discharge of capacitor 24. Capacitor 44 charges to the same potential as capacitor 24. Consequently when the semiconductor controlled rectifier 46 is gated on the potential at the anode of the semiconductor controlled rectifier will drop with respect to the voltage across capacitor 44 and diode 64 will conduct thus turning on the enabling transistor 16 by applying a pulse to control electrode 60. Diode 45 isolates the capacitor 24 from the capacitor 44, diode 64 and resistor 65 of the control circuitmeans of the enabling transistor. Consequently, with the semiconductor controlled rectifier turned on and conduction occurring, the response time of the enabling transistor 16 is rapid. Without diode 45, capacitor 24, because of its size and resultant time constant, would have an adverse effect on the speed with which charging would commence.

As the semiconductor controlled rectifier is turned on the control or base electrode 60 has a change in voltage and the voltage across the transistor 16 drops sharply. The voltage then returns to its original value with the semiconductor controlled rectifier being turned off, thereby creating a pulse. The pulse driving through capacitor 62 then actuates the saturable oscillator 41 by turning on transistor 14 to charge capacitor 24.

With the discharge of capacitor 24, diode 52 provides a feedback path resulting in a ringout oscillation between the ignition capacitor 24 and the winding 48. Variable resistance 49 limits the peak voltage operating similarly to a zener diode. The ringout oscillation is very rapidly damped. When utilized in a conventional outboard motor the ignition transformer, as illustrated by oscillating voltage wave 58, will be damped below the minimum spark gap arcing voltage level in approximately microseconds, as illustrated by oscillating voltage wave 58. An alternating current spark is effected at spark gap 54 as activated by the high voltage ignition transformer 50. The alternating current spark at spark gap 54 prevents the hot oil and gas mixture in the cylinder from depositing in the spark gap. The invention thus prevents spark gap fouling and reduces the frequency of spark plug replacement.

What we have, therefore, is an initiation circuit for a capacitor discharge ignition system which includes an enabling circuit for preventing overcharging of the ignition capacitor, protecting the semiconductor controlled rectifier from high voltage spikes of short duration, prolonging the semiconductor controlled rectifiers useful life, and improving the response time of the oscillating circuit for charging the ignition capacitor.

1 claim:

1. An initiation circuit for a capacitor discharge ignition system for an internal combustion engine comprising an ignition capacitor; a semiconductor trigger means for discharging said ignition capacitor in synchronism with the engine to produce ignition pulses, said semiconductor trigger means having a gate, an input and an output; an oscillating circuit comprising a power transistor having control and output electrodes,

a transformer having a primary winding connected between said output of said power transistor and a reference potential and having first and second inductively coupled secondary windings, and circuit means for coupling said first secondary winding between said output and control electrode of said power transistor, said primary inducing current in said first secondary winding to drive said-power transistor into saturation; an enabling circuit having an enabling transistor with control, output and common electrodes with said common electrode being connected to a reference potential, a zener diode connected between said output and common electrodes and poled to prevent changes in the magnitude of the supply potential from initiating the power transistor of said oscillating circuit, control circuit means coupling said input of said semiconductor controlled rectifier to said control electrode of said enabling transistor, said output electrode of said enabling transistor being responsive to the operation of the semiconductor trigger means to couple a signal from the input of the trigger means to the control electrode of the power transistor; capacitor means coupled between said output electrode of said enabling transistor and said control electrode of said power transistor to isolate said enabling transistor from said oscillating circuit; a supply potential coupled to said common electrode of said power transistor; circuit means coupling said supply potential to the output of said enabling transistor, a first electron control device and said secondary winding of said transformer in series and coupled across said ignition capacitor with induced pulses of one polarity from said second secondary winding charging said ignition capacitor; and an ignition transformer having primary and secondary windings and connected to said output of said semiconductor trigger means.

2. An initiation circuit for a capacitor discharge ignition system according to claim 1 wherein said control circuit means includes a diode providing isolation from said ignition capacitor to improve the response time of said enabling transistor.

3. An initiation circuit for a capacitor discharge ignition system according to claim 1 wherein said control circuit means includes a capacitor connected between the input of said trigger means and said reference potential for filtering out voltage spikes resulting from said saturable oscillator turning off.

4. An initiation circuit for a capacitor discharge ignition system according to claim 1 including an electron control device connected between said primary of said ignition transformer and said ignition capacitor to provide a feedback path for producing a ringout oscillation between the ignition capacitor and said ignition transformer, said ringout oscillation producing an alternating current across said spark gap.

5. An initiation circuit for a capacitor discharge ignition system for an internal combustion engine comprising an ignition capacitor; a semiconductor controlled rectifier for discharging said ignition capacitor in synchronism with the engine to produce ignition pulses, said semiconductor controlled rectifier having a gate, an anode, and a cathode; a power transistor for charging said ignition capacitor, said power transistor having control, output and common electrodes, a supply potential coupled to said reference electrode of said power transistor; a transformer having first, second and third inductively coupled windings with the output electrode of said power transistor being coupled to said first winding; circuit means for connecting said second winding to said control electrode of said power transistor with increases in current in said first winding increasing current in said second winding and driving said power transistor into saturation with said ignition capacitor being charged; a first diode and said third winding in series and coupled across said ignition capacitor with induced pulses of one polarity in said third winding charging said ignition capacitor; an enabling circuit having an enabling transistor with control, output and common electrodes, control circuit means coupling said control electrode of said enabling transistor to said anode of said semiconductor controlled rectifier for activating said enabling transistor, said output electrode of said enabling transistor being coupled .to said supply potential, and said common electrode being coupled to said reference potential; a zener diode being connected between said common and output electrodes of said enabling transistor and being poled to prevent changes in magnitude of said supply potential from initiating said power transistor; an ignition transformer having a primary winding and a secondary winding and being connected to the cathode of said semiconductor controlled rectifier; a capacitor coupled between said output of said enabling transistor and said control electrode of said power transistor for initiating said power transistor with said enabling transistor being activated; first diode means coupled between said ignition capacitor and said anode of said semiconductor controlled rectifier means to improve the response time of said enabling transistor, second diode means coupled between said output of said trigger means and said ignition capacitor and poled to create a ringout oscillation between said ignition capacitor and said primary of said ignition transformer for producing an alternating current ignition pulse, a capacitor connected between said anode of said semiconductor controlled rectifier means and said reference potential to filter turnoff spikes from said third winding with said power transistor turning off to prevent damage to said semiconductor controlled rectifier means.

Claims (5)

1. An initiation circuit for a capacitor discharge ignition system for an internal combustion engine comprising an ignition capacitor; a semiconductor trigger means for discharging said ignition capacitor in synchronism with the engine to produce ignition pulses, said semiconductor trigger means having a gate, an input and an output; an oscillating circuit comprising a power transistor having control and output electrodes, a transformer having a primary winding connected between said output of said power transistor and a reference potential and having first and second inductively coupled secondary windings, and circuit means for coupling said first secondary winding between said output and control electrode of said power transistor, said primary inducing current in said first secondary winding to drive said power transistor into saturation; an enabling circuit having an enabling transistor with control, output and common electrodes with said common electrode being connected to a reference potential, a zener diode connected between said output and common electrodes and poled to prevent changes in the magnitude of the supply potential from initiating the power transistor of said oscillating circuit, control circuit means coupling said input of said semiconductor controlled rectifier to said control electrode of said enabling transistor, said output electrode of said enabling transistor being responsive to the operation of the semiconductor trigger means to couple a signal from the input of the trigger means to the control electrode of the power transistor; capacitor means coupled between said output electrode of said enabling transistor and said control electrode of said power transistor to isolate said enabling transistor from said oscillating circuit; a supply potential coupled to said common electrode of said power transistor; circuit means coupling said supply potential to the output of said enabling transistor, a first electron control device and said secondary winding of said transformer in series and coupled across said ignition capacitor with induced pulses of one polarity from said second secondary winding charging said ignition capacitor; and an ignition transformer having primary and secondary windings and connEcted to said output of said semiconductor trigger means.

2. An initiation circuit for a capacitor discharge ignition system according to claim 1 wherein said control circuit means includes a diode providing isolation from said ignition capacitor to improve the response time of said enabling transistor.

3. An initiation circuit for a capacitor discharge ignition system according to claim 1 wherein said control circuit means includes a capacitor connected between the input of said trigger means and said reference potential for filtering out voltage spikes resulting from said saturable oscillator turning off.

4. An initiation circuit for a capacitor discharge ignition system according to claim 1 including an electron control device connected between said primary of said ignition transformer and said ignition capacitor to provide a feedback path for producing a ringout oscillation between the ignition capacitor and said ignition transformer, said ringout oscillation producing an alternating current across said spark gap.

5. An initiation circuit for a capacitor discharge ignition system for an internal combustion engine comprising an ignition capacitor; a semiconductor controlled rectifier for discharging said ignition capacitor in synchronism with the engine to produce ignition pulses, said semiconductor controlled rectifier having a gate, an anode, and a cathode; a power transistor for charging said ignition capacitor, said power transistor having control, output and common electrodes, a supply potential coupled to said reference electrode of said power transistor; a transformer having first, second and third inductively coupled windings with the output electrode of said power transistor being coupled to said first winding; circuit means for connecting said second winding to said control electrode of said power transistor with increases in current in said first winding increasing current in said second winding and driving said power transistor into saturation with said ignition capacitor being charged; a first diode and said third winding in series and coupled across said ignition capacitor with induced pulses of one polarity in said third winding charging said ignition capacitor; an enabling circuit having an enabling transistor with control, output and common electrodes, control circuit means coupling said control electrode of said enabling transistor to said anode of said semiconductor controlled rectifier for activating said enabling transistor, said output electrode of said enabling transistor being coupled to said supply potential, and said common electrode being coupled to said reference potential; a zener diode being connected between said common and output electrodes of said enabling transistor and being poled to prevent changes in magnitude of said supply potential from initiating said power transistor; an ignition transformer having a primary winding and a secondary winding and being connected to the cathode of said semiconductor controlled rectifier; a capacitor coupled between said output of said enabling transistor and said control electrode of said power transistor for initiating said power transistor with said enabling transistor being activated; first diode means coupled between said ignition capacitor and said anode of said semiconductor controlled rectifier means to improve the response time of said enabling transistor, second diode means coupled between said output of said trigger means and said ignition capacitor and poled to create a ringout oscillation between said ignition capacitor and said primary of said ignition transformer for producing an alternating current ignition pulse, a capacitor connected between said anode of said semiconductor controlled rectifier means and said reference potential to filter turnoff spikes from said third winding with said power transistor turning off to prevent damage to said semiconductor controlled rectifier means.

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