US3720194A

US3720194A - Ignition system

Info

Publication number: US3720194A
Application number: US00145276A
Authority: US
Inventors: M Mallory
Original assignee: Mallory Electric Corp
Current assignee: Mallory Inc; Mallory Electric Corp
Priority date: 1971-05-20
Filing date: 1971-05-20
Publication date: 1973-03-13
Anticipated expiration: 1990-03-13

Abstract

IS SUFFICIENT TO EXCITE THE ELECTRONIC SWITCH TO CONDUCT THUS DISCHARGING THE CAPACITOR THROUGH THE PRIMARY WINDING OF THE STEP-UP TRANSFORMER.

A CAPACITIVE-DISCHARGE MAGNETO IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES IS PROVIDED. THE MAGNETO OUTPUT IS UTILIZED DURING ONE-HALF CYCLE TO CHARGE A CAPACITOR. DURING THE INITIAL STAGES OF THE HALF CYCLE, THE MAGNETO OUTPUT IS DISCHARGED TO GROUND THROUGH CONVENTIONAL POINTS. THE POINTS ARE OPENED AT A PREDETERMINED VOLTAGE LEVEL WHEREUPON DISCHARGE TO GROUND TERMINATES AND THE CAPACITOR IS CHARGED. THE CAPACITOR IS CONNECTED THROUGH THE PRIMARY WINDING OF A STEP-UP TRANSFORMER WHICH IN TURN IS CONNECTED TO A SPARKING DEVICE. A TRIGGER WINDING IS INDUCTIVELY COUPLED TO THE MAGNETO WINDING. THE OUTPUT OF THE TRIGGER WINDING IS CONNECTED TO THE EXCITAION CIRCUIT OF AN ELECTRONIC SWITCH WHICH COMPLETES A CIRCUIT FROM THE CAPACITOR TO GROUND. A VOLTAGE IS INDUCED IN THE TRIGGER WINDING UPON COLLAPSE OF THE FIELD OF THE MAGNETO WINDING. THE MAGNETO WINDING FIELD COLLAPSES WHEN THE CAPACITOR IS CHARGED. THE INDUCED VOLTAGE

Description

March 13, 1973 M. MALLORY, JR

IGNITION SYSTEM Filed May 20, 1.971

8 2 :m 3 2 3 \II 2 \II 5 WI 4 m 3 M rt. 0 I 4 8 3 g 2 INVENTOR N MALLORY, JR.

ATTORNEYS United States Patent US. Cl. 123-148 E 6 Claims ABSTRACT OF THE DISCLOSURE A capacitive-discharge magneto ignition system for internal combustion engines is provided. The magneto output is utilized during one-half cycle to charge a capacitor. During the initial stages of the half cycle, the magneto output is discharged to ground through conventional points. The points are opened at a predetermined voltage level whereupon discharge to ground terminates and the capacitor is charged. The capacitor is connected through the primary Winding of a step-up transformer which in turn is connected to a sparking device. A trigger winding is inductively coupled to the magneto winding. The output of the trigger winding is connected to the excitation circuit of an electronic switch which completes a circuit from the capacitor to ground. A voltage is induced in the trigger winding upon collapse of the field of the magneto winding. The magneto winding field collapses when the capacitor is charged. The induced voltage is sufficient to excite the electronic switch to conduct thus discharging the capacitor through the primary winding of the step-up transformer.

BACKGROUND OF THE INVENTION Many different capacitive-discharge systems have been proposed in the past as modifications of the conventional battery-coil type of ignition system for internal combustion engines. However, capacitive discharge techniques have been difficult to apply to magneto ignition systems. Magneto ignition systems generate sparking voltages from mechanical motion. A magneto ignition system employs a magneto as the source of the primary voltage for generating the necessary high sparking voltage. A magneto is essentially an AC generator comprising either a fixed magnetic field and a revolving armature winding or a revolving magnetic field and a fixed winding. Magneto ignition systems are very similar in most respects to battery-coil ignition systems, employing breaker contacts and condensers as do battery-coil systems. Magnetos generally have poor low-speed characteristics but excellent high-speed characteristics. As a consequence, magneto systems, while not in general use, are widely used in high performance vehicles such as racing cars.

The present invention provides a capacitive-discharge magneto system. The system includes structure which isolates the breaker points from the inductive load of the primary winding of the step-up transformer forming the output coil of the system. This isolation improves point life to a considerable extent, current tests indicating that there is virtually no damage to the points caused by sparking. Additionally, means for automatically discharging the capacitor through the primary winding of the output coil are provided to operate instantly upon charging of the coil. These means comprise a trigger winding inductively coupled to the magneto winding. This avoids mechanical timing structure along with the attendant lack of reliability and maintenance problems such structures inherently present.

SUMMARY OF THE INVENTION The capacitive-discharge magneto ignition system for internal combustion engines includes a step-up transformer 3,720,194 Patented Mar. 13, 1973 ice having primary and secondary windings. A capacitor is placed in series with the primary winding. A magneto including a magneto winding is provided. The output side of the magneto winding is connected to the capacitor to charge the capacitor. A mechanical switch is provided between the magneto output and ground. Means to close the mechanical switch during the initial portions of a half-cycle of magneto operation and open the mechanical switch at a predetermined voltage level of a half-cycle of magneto operation to cause charging of the capacitor are provided. A trigger winding is inductively coupled to the magneto winding. An electronic switch is provided. The electronic switch includes a first circuit connected between one side of the capacitor and ground. The electronic switch also includes an excitation circuit which, upon reception of an electric pulse of predetermined magnitude, causes the electronic switch to conduct through the first circuit. The other side of the capacitor is connected to the primary winding of the transformer. The output side of the trigger winding is connected to the excitation circuit. The trigger winding has a voltage induced therein sufiicient to cause the electronic switch to conduct and thus discharge the capacitor through the primary winding of the step-up transformer upon a collapse of the magneto field which occurs with the mechanical switch open after the capacitor is charged.

In the drawing:

The figure is a schematic illustration of one embodiment of the capacitive-discharge magneto ignition system of the present invention.

The magneto ignition system illustrated in the figure includes, as a source of electrical power, an inductor-type magneto 10. An armature-type magneto may, if desired, be substituted for the inductor-type magneto. The magneto 10 includes permanent magnet 12 rotatably mounted within a magneto yoke 14. A pair of

windings

16, 18 are wound on the the yoke '14. The winding 16 has considerably more turns than the winding 18 and serves as the regular magneto winding. When the magnet 12 is rotated in the direction indicated by arrow 20, the magnetic lines of force which form the magnetic field generated by the magnet induce a voltage in the Winding 16 which is ultimately utilized to cause sparking of a spark gap device 22. The device 22 is the usual spark plug provided in an internal combustion engine. Only one spark gap device is illustrated. However, it will be appreciated that the ignition circuit may be utilized in various internal combustion engines which may have, for example, six, eight, or more spark plugs. Contrariwise, the ignition system may be utilized in internal combustion engines having only one spark gap device.

The second winding 18 termed a trigger winding has only a few turns and is utilized as a means for triggering a controlled rectifier 24 into the conducting state. The trigger winding 18 generates a signal capable of initiating conduction in the controlled rectifier 24 in timed relation to the operation of the engine.

One end of the winding 16 is tied to a ground 26 which is common to both of the windings. The other end of the winding 16 is connected to a solid state diode device 28 by means of lead 30. The output side of the diode 28 is connected to one side of a capacitor 32 via lead 33. The other side of capacitor 32 is connected to one end of a winding 34 by means of lead 36. The winding 34 forms the primary winding of step-up transformer 38, usually referred to as the output coil. One end of the secondary winding 40 is connected to the spark gap device 22 via lead 41, it being appreciated that the usual distributor may be interposed between winding 40 and a plurality of spark gap devices. The other ends of

windings

34, 40 are connected to a common ground 42.

A lead '44 extends from the lead 33 from a point between capacitor 32 and diode 28 to ground. Conventional breaker points 46 are provided in lead 44. As is conventional, the breaker points are opened and closed in timed relation to engine operation by means of a camming device 45. A lead 48 extends from lead 44 from a point be tween the breaker points 46 and the lead 33 to ground. A capacitor 50 is provided in lead 48. The capacitor 50' performs the usual function of protecting the breaker points against undue flashing upon opening of the points.

A lead 52 extends from lead 33 to ground from a point between the capacitor 32 and the connection of lead 44. The controlled rectifier 24 is provided in lead 52. The rectifier 24, which may be a silicon controlled rectifier, has an anode 54, a cathode 56 and a gate 58. As is Well known, a controlled rectifier is a solid state four-layer device. In its normal state, the controlled rectifier acts as an open circuit. It will not pass current. When an appropriate voltage or current pulse is applied to the gate electrode, it will cause the controlled rectifier to be forward biased to permit current flow. Application of the proper polarity voltage to the controlled rectifier will allow electrons to flow from the cathode to the anode. Once in the conducting state it will remain so until the main current is reduced to a small current called the holding current. Then it returns to the blocking state and remains so until it is triggered again. Thus, the controlled rectifier can act as a controlled switching device capable of being switched on or off by application of voltages of appropriate polarity.

The output of the trigger winding 18 is connected to the gate 58 via lead 60. A solid state diode device 62 is provided in lead 60 between the output of the winding 18 and the gate 58.

Operation of the circuit may now be understood. In normal operation of the magneto 10, both a positive and negative voltage is induced in the winding 16 depending upon the position of the north or south poles of the magnet 12. In the present circuit, only the positive component of the induced voltage is utilized. Both components could be utilized if desired. This would require providing parallel circuits. With the circuit shown, the diode 28 blocks the negative component while permitting the positive component to pass thereby.

On a positive cycle of the output of the magneto the points 46 are closed at the beginning of the cycle. Thus, the entire output of the magneto is bypassed to ground during the initial stages. At a time when the induced voltage approaches a maximum, the points 46 are caused to open. This causes charging of the capacitor 32. Arcing of the points 46 is virtually eliminated as a result of provision of the capacitor 32 along with the usual capacitor 50. Point life is additionally greatly improved because the points are not interrupting the inductive load of transformer 38. Tests indicate that with the present circuit, point life should be almost indefinite. After the capacitor 32 has been charged to the highest potential emitted by the winding 16, the field about the winding 16 rapidly collapses because the winding at this time sees an open circuit.

The highest potential induced into winding 16 occurs when the rate of change of magnetic force lines is greatest. This happens when the magnet 12 is at right angles to the yoke faces. The points 46 are preferably arranged to open when this condition occurs. In one actual model of the circuit, the maximum voltage emitted by the magneto was in the range of 400 to 500 volts. However, different windings may be used to raise or lower the voltage depending upon the requirements of the overall circuit. Discharge of the capacitor 32 back through the winding 16 upon collapse of its field is prevented by the blocking nature of diode 28.

The rapid collapse of the field about winding 16 induces a relatively high voltage in the trigger winding 18. This voltage is higher than that induced in winding 18 by rotation of the'magnet 12 because the collapse of the field about winding 16 occurs very rapidly. The voltage induced 4 in winding 118 is sutficient to trigger the controlled rectifier 24 into the conducting state. The diode 62 insures that only a voltage of the proper polarity will be passed to the controlled rectifier 24. In one actual embodiment, the triggering voltage was in the range of 60 to 70 volts which, of course, may be altered by varying the number of turns of the winding 18 to suit the requirements of the particular rectifier 24 being used.

It should be noted that the capacitor 32 is always fully charged before the rectifier 24 is triggered to conduct although the rectifier 24 is triggered to conduct almost immediately after the capacitor 32 is charged, it being appreciated that charging the capacitor 32 is the causative factor in the collapse of the field about winding 16 which in turn is the causative factor for inducing the triggering voltage in winding 18. This automatic timing is of importance in that it eliminates the need for mechanical timing devices and the inherent problems caused in connection with the use thereof.

When the controlled rectifier 24 begins to conduct, the capacitor 32 rapidly discharges through the primary winding 34 of transformer 38 inducing a voltage in secondary winding 40 sutficient to cause sparking. This action is the same as in a conventional capacitive-discharge ignition system. Upon discharge of the capacitor 32, the current available to the controlled rectifier 24 is minimized, reaching the holding current level whereupon the rectifier 24 will return to the blocking state and remain so until it is again triggered.

The points 46 are then caused to again close thus returning the circuit to its original state. The points 46 are not opened during the negative half cycle of the magneto 10 because the illustrated system is adapted to only handle a one-half cycle, exemplary the positive halfcycle. As previously mentioned, both half-cycles may be used by providing parallel circuits.

What I claim as my invention is:

1. A capacitive-discharge magneto ignition system for internal combustion engines comprising a step-up transformer having primary and secondary windings, a capacitor in series with the primary winding, a magneto including a magneto winding, the output side of the magneto winding being connected to the capacitor to charge the capacitor, a mechanical switch between the magneto output and ground, means to maintain said switch closed during the initial portions of a half-cycle of magneto operation and open said switch at a time when the voltage level of a half-cycle of magneto operation approaches a maximum to cause charging of the capacitor, a trigger winding inductively coupled to the magneto winding, an electronic switch including a first circuit connected between one side of the capacitor and ground, the other side of the capacitor being connected to the primary winding of said transformer, said electronic switch including an excitation circuit for initiating conduction through said first circuit upon reception of an electrical pulse of predetermined magnitude, the output side of the trigger winding being connected to said excitation circuit, said trigger winding having a voltage induced therein suificient to cause the electronic switch to conduct through said first circuit and thus discharge the capacitor through said primary winding upon a collapse of the magneto field which occurs with said mechanical switch open after the capacitor is charged.

2. An ignition system as defined in claim 1, further characterized in that said electronic switch is a solid state switch including a gate, an anode and a cathode, the anode-cathode circuit comprising said first circuit, said gate forming part of said excitation circuit, the output side of the trigger winding being connected to said gate.

3. An ignition system as defined in claim 1, further characterized in the provision of a diode between said capacitor and magneto winding acting to pass current to charge said capacitor and block discharge of the capacitor through the magneto winding.

4. An ignition system as defined in claim 1, further characterized in the provision of a diode between the trigger winding and the excitation circuit acting to pass current of a polarity to cause excitation of the electronic switch and to block current of the opposite polarity.

5. An ignition system as defined in claim 1, further characterized in that said magneto includes a yoke, said magneto winding and said trigger winding both being wound on said yoke.

6. A capacitive-discharge magneto ignition system for internal combustion engines comprising a step-up transformer having primary and secondary windings, a capacitor in series with the primary winding, a magneto including a magneto winding, the output side of the magneto winding being connected to the capacitor to charge the capacitor, a mechanical switch between the magneto output and ground, means to maintain said switch closed during the initial portions of a half-cycle of magneto operation and open said switch at a time when the voltage level of a half-cycle of magneto operation approaches a maximum to cause charging of the capacitor, a trigger winding inductively coupled to the magneto winding, an electronic switch including a first circuit connected between one side of the capacitor and ground, the other side of the capacitor being connected to the primary Winding of said transformer, a diode between said capacitor and magneto winding acting to pass current to charge said caapcitor and block discharge of the capacitor through the magneto winding, said electronic switch including an excitation circuit for initiating conduction through said first circuit upon reception of an electrical pulse of predetermined magnitude, the output side of the trigger winding being connected to said excitation circuit, a diode between the trigger Winding and the excitation circuit acting to pass current of a polarity to cause excitation of the electronic switch and to block current of the opposite polarity, said trigger winding having a voltage induced therein sufficient to cause the electronic switch to conduct through said first circuit and thus discharge the capacitor through said primary winding upon a collapse of the magneto field which occurs with said mechanical switch open after the capacitor is charged.

References Cited UNITED STATES PATENTS 3,620,200 11/1971 Stephens 123-148 B 3,367,314 2/1968 Hirusawa.

3,524,438 8/ 1970 Janisch.

3,584,929 6/1971 Schuette.

3,545,419 12/1970 Nocting.

2,256,907 9/ 1941 Oschsenbein.

OTHER REFERENCES SAE Journal, July 1963, McClelland and Zoll Breakerless High Frequency Ignition, pp. 74-78.

LAWRENCE M. GOODRIDGE, Primary Examiner R. B. COX, Assistant Examiner US. Cl. XQR. 123149 A