US3427502A

US3427502A - Capacitor ignition system

Info

Publication number: US3427502A
Application number: US526732A
Authority: US
Inventors: Floyd M Minks
Original assignee: Brunswick Corp
Current assignee: Brunswick Corp
Priority date: 1966-02-11
Filing date: 1966-02-11
Publication date: 1969-02-11
Anticipated expiration: 1986-02-11

Description

Feb. 11, F M, M|NKS CAPACITOR IGNITION SYSTEM Filed Feb. 11, 1966 f N" i-#%\ I -55 N 1 D E 0- x MW? I INVENTOR flora M Mums 3,427,502 CAPACITOR IGNITION SYSTEM Floyd M. Minks, 'Campbellsport, Wis., assignor, by mesne assignments, to Brunswick Corporation, Chicago, III., a corporation of Delaware Filed Feb. 11, 1966, Ser. No. 526,732 US. Cl. 315-209 10 Claims Int. Cl. H01g 9/00; H01t 15/02 ABSTRACT OF THE DISCLOSURE The disclosure relates to triggering of a triggered capacitor discharge ignition system. The contacts of the point assembly such as conventionally employed for many years are serially connected in series circuit with the primary winding of a pulse transformer having the secondary winding connected to the gate of a controlled rectifier which is connected to turn on a blocking oscillator of a capacitor discharge ignition circuit. The inductance of the transformer stores energy in the core during the period the point contacts are closed and rapidly discharges the energy through the secondary winding when the contacts open to fire the rectifier. The blocking oscillator is connected directly to the battery or power supply and the ignition switch is only connected in series with the points and the primary.

This invention relates to a capacitor ignition system or the like and particularly to an improved pulse circuit for the formation of a start or trigger pulse in an internalcombustion engine ignition system and the like.

Electronic ignition systems for internal-combustion engines have been suggested for a number of years wherein a capacitor is charged from the battery and/or the generator and is rapidly discharged through the induction coil of the usual ignition unit to fire a spark plug. The recent development of solid state devices such as transistors, silicon controlled rectifiers and the like provided a highly satisfactory amplifying and switching means for controlled charging and switching of the capacitor circuit. A highly satisfactory capacitor discharge ignition system is shown in applicants copending application entitled, Triggered Ignition System, which was filed on Oct. 4, 1965, with Ser. No. 492,571, now abandoned, and assigned to a common assignee.

In the above application, a triggered blocking oscillator is provided having a control circuit connected in the feedback circuit to determine the time that each pulse begins and the energy per pulse. In a preferred construction, a transistor is connected in series with the primary of an oscillator transformer to a battery. The transformer is connected to charge a capacitor which is subsequently discharged through the spark gap by triggering or firing of a main controlled rectifier. A triggering and feedback circuit employs a control transistor connected in the base circuit of the main or charging transistor with the input of the control transistor connected in circuit through a turn-on controlled rectifier. The main rectifier is fired from a pulse transformer inserted in the base circuit of the charging transformer. The gate of the turn-on controlled rectifier and the base of the control transistor are connected to a suitable signal source which in turn is controlled in accordance with the timing of the internalcombustion engine to provide periodic turn-on pulses to the controlled rectifier.

The present invention is particularly directed to the improvement in the triggering means for a triggered ignition system and particularly for the start or turn-on controlled rectifier. In accordance with the present invention,

nited States Patent the contacts of the point assembly such as conventionally employed for many years are serially connected in circuit with a pulse transformer or trigger inductor having an output winding connected to the trigger means of the controlled rectifier. The inductance of the transformer stores energy in the core during the period the point contacts are closed and rapidly discharges the energy through the secondary winding 32 when the contacts open to fire the rectifier.

The transformer produces a relatively high voltage, low current pulse in the primary which yields maximum contact life and reliability.

The drawing furnished herewith illustrates a preferred construction of the present invention in which the above advantages and features are clearly disclosed as well as others which will be clear from the following description of the drawing.

In the drawing:

FIG. 1 is a schematic circuit diagram of an ignition system constructed in accordance with the present invention; and

FIG. 2 is a diagrammatic view of a trigger inductor shown in FIG. 1.

Referring to the drawing and particularly to FIG. 1, the illustrated ignition system is connected to a direct current source such as a low voltage battery 1 having a suitable rated output voltage such as 6, 12 or 24 volts all of which are presently employed in automobiles, trucks, outboard motors or other similar internal-combustion engines. A single spark gap 2 is illustrated forming a part of a combustion chamber of the prime mover. In multicylinder engines, a plurality of spark gaps will normally be employed with a distributor 3, shown in block diagram, provided to sequentially distribute the power to the several gaps in accordance with known practice. A main firing transformer 4 couples the spark gap 2 to a capacitor discharge circuit including a storage capacitor 5 connected to be discharged through the transformer 4 in series with a silicon controlled rectifier 6.

The capacitor 5 is connected to be charged from the battery 1 through a triggered blocking oscillator 7 which includes a charging transformer or inductance unit 8 and a square loop core unit 9 to regulate the energy per capacitor charging pulse.

A pulse transformer 10 is connected in the circuit of blocking oscillator 7 and to the controlled rectifier 6 to fire the rectifier in timed relation to the operation of the internal-combustion engine and the distributor 3 as hereinafter described and thereby causes proper transfer of energy from the capacitor 5 to gap 2.

The illustrated ignition system generally corresponds to that of the previously identified application which also discloses the novel trigger circuit 11 which forms the subject matter of the present invention. Consequently, the ignition system is generally only briefly described in sufficient detail to clearly explain the operation of the present invention.

An input switch 12 which may be the usual points employed with internal-combustion engines is coupled to be mechanically actuated in synchronism with the operation of the engine, diagrammatically shown coupled to the operation of the distributor 3, to provide periodic triggering of the blocking oscillator 7 into conduction.

The oscillator 7 generally includes a charging transistor 13 connected in series with a primary 14 of the transfer or oscillating transformer 8, shown as an autotransformer. A secondary 15 of transformer 8 is connected in a charging circuit with the capacitor 5 and a charging diode 16. The circuit is such that during the conduction through the primary 14 from the battery 1, the diode 16 opens the circuit of capacitor 5. When the current through the transformer primary 14 is cut off, a pulse is generated in the secondary 15 which charges the capacitor 5, as described in the previously referred to application. This charge is transmitted to the gap 2 as noted above, at the next initiation of conduction of the oscillator 7.

Generally, the circuit operation includes closing of switch 12 to charge the trigger circuit 11. When switch 12 opens, the trigger circuit 11 initiates operation of the oscillator 7 which derives power from the battery 1 with a portion of the current passing through the square loop core unit 9. The turn-on current energizes the transformer 10 to fire controlled rectifier 6 and discharge the previous charge on capacitor 5. When the square loop core unit 9 is saturated, it will rapidly turn off the oscillator 7. The collapsing field in transformer 3 produces a current in the secondary which charges capacitor 5 to a corresponding level. When the switch 12 again opens to initiate the conduction of oscillator 7, pulse transformer 10 is again energized and the silicon controlled rectifier 6 is fired to discharge the capacitor 5. The capacitor 5 is therefore charged and discharged in timed relation to the operation of the distributor 3 and the movement of the piston, not shown, to provide proper transfer of energy pulses from the capacitor 5 through the pulse transformer 4 to the gap 2.

More particularly in the illustrated embodiment of the invention, the oscillator circuit includes the transistor 13 shown as a PNP type, connected in a common emitter con figuration; having an emitter 17 connected to the positive side of the battery 1 and a collector 18 connected to the one side of the primary winding 14. The opposite side of the winding 14 is connected to the negative side of the battery 1 through a common ground connection. The transistor 13 includes a base 19 as an input means or element which is connected to derive its power from the battery 1 as follows.

The base 19 is connected to the negative terminal of the battery 1 through the pulse transformer 10, a current limiting resistor 20 which desirably has a resistance value which increases with increasing current flow through it and a transistor 21 to ground.

The pulse transformer 10 is a relatively compact and small unit having a primary winding 22 connected in series with the base 19 and having a secondary winding 23 connected to the gate of the silicon controlled rectifier 6. The secondary winding 23 is close coupled to the primary winding 22 by a suitable core 24 preferably a small ferrite core. The transformer acts as a current transformer having the property or characteristic of being saturated in a time small compared with the time required to store the required energy in transformer 8. As a result, the initial oscillator turn-on current in the base loop of the transistor 13 in passing through primary winding 22 generates a pulse in the secondary winding 23. The pulse terminates on saturation of the core 24.

The resistor 20 has a sharply changing resistance with current passing through it. This is a result of a high positive temperature coefiicient of the resistance element coupled with a controlled thermal impedance from the resistance element to its surroundings.

The control transistor 21 is shown as an NPN type having the collector to emitter circuit in the above base circuit and a base to emitter circuit connected between the collector 18 of transistor 13 and the ground in a control circuit branch to derive power from the collector 18 of transistor 13 after initiation of the triggering of the blocking oscillator 7. The connection to the collector 18 is through resistors 25 and resistor 26 and a silicon controlled rectifier 27 to provide a selectively completed or triggered voltage dividing network.

The silicon controlled rectifier 27 includes a gate 28 which controls conduction through the rectifier and the control circuit branch.

The gate 28 is connected to the battery 1 through the current limiting resistor 35 and a novel trigger circuit 11 including a pulse transformer 29, resistor 34 and switch 12, as follows.

Switch 12 is connected to the positive side of battery 1 in series with the primary winding 30 of the pulse transformer 29 and an on-off control switch 31. The opposite side of the switch 12 is connected to the negative side of the battery 1 through a ground connection.

The pulse transformer 29 includes a secondary winding 32 magnetically coupled to the primary winding 30 by a core unit 33 and wound to produce the indicated polarities.

The secondary winding 32 is connected in parallel with a resistor 34 between ground and a current limiting resistor 35 which is connected to the gate 28 of the silicon controlled rectifier 27. The paralleled resistor 34 serves to critically damp the distributed capacity associated with windings 30 and 32. A resistor 35a is connected between the base of transistor 21 and the gate resistor 35 to increase the excitation of transistor 21 during the initial turn-on period. Further, a capacitor 39 is connected across the transformer 8 to assist in the turnoff of the rectifier 27 When points or switch 12 close, current flows through the primary 30 and the switch 12 with energy being stored in the core 33. When the points or switch 12 open, the primary 30 acts as a high voltage, low current source impressed across the points or switch 12. This produces a controlled arc across the points and produces an output trigger voltage insensitive to engine speed and battery voltage. The current through the points is directly proportional to the battery voltage and decreases expotentially as engine speed increases. In a typical system, the current may vary from a few milliam-peres, of the order of 10 ma., at high engine speeds to a fraction of an ampere, of the order of .1 ampere, at low engine speed. These currents are sufficiently low to prevent burning of the contacts but sufficiently high to essentially eliminate detrimental effects of oxidation.

The triggering circuit therefore provides a particularly simple and inexpensive system which can employ well known and readily available ignition point units.

The pulse transformer preferably is constructed in accordance with the construction of FIG. 2 wherein the core unit 29 includes a pair of E-shaped ferrite cores 36 and 37 mounted with the ends of the legs adjacent each other to define a three-legged core unit. The legs are separated slightly by nonmagnetic spacers 38 to define a small air gap in the magnetic circuits through the several legs. The primary winding 30 and the secondary winding 32 are wound about the central leg. Typical circuit values for a practical 12 volt ignition system may include:

Winding 3t) 180'0 turns, ohms, .4 henries. Winding 32 50 turns.

Resistor 34 33 ohms.

Resistor 35 220 ohms.

Resistor 35a 220 ohms.

The operation of the illustrated embodiment of the invention may be briefly summarized as follows.

The points or other commutating means are coupled to the distributor 3 to be driven in accordance with the movement of the pistons of the internal-combustion engine in accordance with any suitable or known system. The battery 1 provides a source of energy to the oscillator 7 which transfers energy to the capacitor 5 to charge it to a selected level.

When the switch 12 is closed, current flows in the circuit of the transformer or inductor 29 and stores energy in the core 33. The polarity of the primary winding 30 and the secondary winding 32 are opposite that shown in the drawing during the charging cycle and consequently back bias the transistor 21 and rectifier 27. When switch 12 opens, the polarity reverses and a pulse is generated to initiate conduction through the gate circuit of silicon controlled rectifier 27 and the input or base loop of transistor 21. The transistors 11 and 21 then conduct. Conduction in the base loop of transistor 21 generates a pulse in the pulse transformer which is connected to fire the controlled rectifier 6 and thereby discharge the charge placed on the capacitor 5 during the previous cycle of oscillator 7. Conduction in the output loop of transistor 13 provides a charging current to transformer 8 until the square loop core unit 9 is saturated at which time it rapidly turns the oscillator off, terminating the charging of the transformer 8 and the transferring a new charging pulse to the capacitor 5.

The next time the switch 12 is closed, energy begins to be stored in the transformer 29 and prepared the system for recycling in accordance with the above description. The capacitor 5 is therefore sequentially charged and discharged to fire the proper spark gap 2 or gaps in proper sequence in accordance with the operation of the engine.

The use of a separate inductor or transformer 11 in circuit with the points provides a relatively simple and reliable pulse forming circuit which can employ the well known and readily available ignition point systems to maintain an inexpensive input circuit without the problems associated with point burning or oxidation or insufficient trigger voltage caused by low battery voltage.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. In an ignition system for an internal-combustion engine employing a solid state pulse forming circuit having an input means to initiate formation of a pulse, the improvement in the energization of the input means com prising,

contact means connected to be opened and closed in timed relation to the engine operation, and

a pulse forming means including a pulse transformer having a primary winding connected in series with the contact means and a power source means and having a secondary winding connected to the said input means, said primary winding having a substantially greater number of turns than said secondary winding to create a high voltage and low current at the contacts upon opening of said contacts, said current being sufiiciently low to prevent burning of the contacts and sufiiciently large to eliminate detrimental effects of oxidation, such voltage being sufficiently high to produce ionization of the air between the points and thereby produce an output trigger voltage substantially independent of the current through the primary and thereby essentially independent of engine speed or battery voltage.

2. The ignition system of claim 1 wherein said pulse transformer includes a separate primary winding and secondary winding, and a resistor is connected across the secondary winding.

3. The ignition system of claim 1 wherein the pulse transformer includes a core unit having a pair of E-shaped cores with aligned legs, and nonmagnetic spacers between the legs to define small air gaps in the core.

4. The ignition system of claim 3 wherein the primary Winding and the secondary winding are wound in superimposed relation on the central leg.

5. In an ignition system for an internal combustion engine, an energy storage means,

a blocking oscillator connected to charge the storage means, said oscillator including a transistor and an inductor means being coupled to said energy storage means, said transistor having an input bias circuit connecting said transistor in a common emitter connection to said inductor means, said transistor having a base circuit loop including a controlled rectifier means to control the conduction of said transistor, said controlled rectifier means having a gate,

ignition point contacts connected to be actuated in timed relation to the engine operation, and

a pulse transformer having an input winding connected in series with the ignition point contacts and having an output winding connected to the gate, said pulse transformer being wound to generate a triggered pulse for firing said controlled rectifier means upon the opening of the ignition point contacts.

6. The system of claim 5 having means connecting the control rectifier gate and the base of the transistor to said transformer simultaneously energizing the rectifier and transistor.

7. The system of claim 5 having the gate connected to the transformer in series with a resistor and having the base of the transistor connected to the transformer in series with a resistor, said resistors directing selected portions of the current to the gate and to the base.

8. In a capacitor discharge ignition system having a battery power supply and a storage capacitor, comprising an ignition switch,

a converter having an input connected directly to the battery power supply independently of said ignition switch and an output adapted to charge the capacitor to a preselected level and having a first electronic switch means controlling the converter, said electronic switch means having an input circuit,

an output circuit including said capacitor and a triggered switch means,

a series circuit combination including a pulse forming means having a switch means and said ignition switchconnected directly across said battery power supply, means coupling said pulse forming means to said input circuit of the first electronic switch means, and

means connected to periodically actuate said triggered switch means and discharge said capacitor.

9. The ignition system of claim 8 wherein said converter includes a blocking oscillator having an input circuit connected across the battery and includes a bias circuit means biasing said oscillator off. said electronic switch means being connected in said bias circuit means to turn on said blocking oscillator in response to input power through said ignition switch.

10. The ignition system of claim 9, wherein said electronic switch means includes a control transistor and a feedback loop circuit including a controlled rectifier, said controlled rectifier having an input gate connected to said pulse forming means.

References Cited UNITED STATES PATENTS 3,263,124 7/ 1966 Stuermer 315-209 3,302,629 2/ 1967 Shano 315-209 3,334,619 8/1967 Penn 315-209 3,335,320 8/1967 Quinn 315-209 JOHN W. HUCKERT, Primary Examiner.

JERRY D. CRAIG, Assistant Examiner.

US. Cl. X.R.