Magneto ignition system

3,229,162

Jan. 11, 1966

D. C. LOUDON

MAGNETO IGNITION SYSTEM

Filed Dec. 5. 1960

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INVENTOR.

DONALD C. LOUDON

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3,229,162

Patented Jan. 11, 1966

United States Patent Office

3,229,162

MAGNETO IGNITION SYSTEM Donald C. London, Sidney, N.Y., assignor to The Bendix Corporation, Sidney, N.Y., a corporation of Delaware

Filed Dec. 5, 1960,'Ser. No. 73,601 ¹

Claims. (CI. 315—276)

This-invention relates to a novel.apparatus for generating surges of electric current. In the described illustrative embodiment of the invention, the apparatus is use- j ful for the generation of periodic surges of electric current, as in an ignition system for use with an internal combustion engine.

The invention has among its objects the provision of novel apparatus for generating surges of electric current.

A further object of the invention lies in the provision of apparatus of the type indicated which incorporates a coil having inductively coupled primary and secondary windings, the apparatus employing one or more transistors to break the circuit through the primary winding.

A still further object of the invention, in specific embodiments thereof, lies in the provision of apparatus of the type indicated.-including a .magneto having a coil with primary and secondary windings, the apparatus including one or more .transistors for breaking the primary .circuit :in lieu of the customary mechanical breaker -points.

Yet another object of the invention lies in the provision of an improved .ignition circuit including a magneto, .the parts of the circuit being particularly characterized -by their long life, their ability-to sustain elevated operating temperatures for extended periods, and by their freedom from mechanical failure.

The above and further objects and novel features of the invention will more fully appear from the following description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is -for the purpose of illustration only, and is not intended as a definition of the limits of the invention.

The sole figure of the drawing is a schematic wiring diagram of an ignition system for. an internal combustion engine, such ignition system incorporating the improved apparatus for generating surges of electric current in accordance with the present invention.

In the drawing, the reference .character 10 designates the magneto for an internal combustion engine. Such magneto.has a coil with a primary winding 11 and a secondary winding 12, the two windings being inductively coupled to each other and to a magnetic core 14. A rotor 13, schematically shown in -the drawing, is mounted for cooperation with core 14. Rotor 13 carries a suitable number of magnetic poles, alternate ones of such magnetic poles being of opposite magnetic polarity. In the embodiment shown, the ignition system is designed for use with a six-cylinder four-cycle engine. Consequently, the rotor, which is driven at half engine crank shaft speed, carries six magnetic poles.

Secondary winding 12 is connected in a conventional manner to spark plugs of an engine through a distributor. One end of coil 12 is connected to ground by a wire 15. The other end of coil 12 is connected to the center post of the rotor 16 of a distributor 17 by a wire 18. Rotor 16 sequentially cooperates with six angularly spaced contacts, each of which is connected by a wire 19 to one terminal of its spark plug 20. The other terminals of the spark plugs are connected to ground as through the block of the motor (not shown) and a wire 21.

The ends of the primary winding 11 are periodically connected together in a manner approaching a short cir10 cuit, such circuit thereafter being broken in order to cause a rapid decay of the flux in core 14 and thus to induce a substantial voltage in secondary winding 12. Such induced voltage causes a. current surge in discharge circuit 15, 18 and thus the firing of the particular spark plug whose contact then cooperates with distributor rotor 16. The primary circuit of the invention includes transistor means for effecting the closing and breaking of the circuit, thereby eliminating the mechanically operated breaker points customarily employed for such purpose.

One end of primary winding 11 is connected to a first end of Winding 25 of a coil 26 by a wire 22, as shown. The other end of winding 11 is connected by a wire 24 to the corresponding, first end of a second winding 27 of coil 26. Coil 26 has a saturable magnetic core 29 which may be made of the magnetic core material known as “Deltamax?’ Coils 25 and 27. are substantially identical, that is, they have the same number of turns of the same gauge of wire.

The other, second end of the first winding 25 of coil 26 is connected by a wire 30 to the base 31 of a first transistor 32. The emitter 34 of transistor 32 is connected to wire 22 by a wire- 35. A second transistor 39 is connected in the same manner between the second end of winding 27 of coil 26 and wire 24. Thus a wife 36 extends from the second end of winding 27 to the base 37 of a second transistor 39, and the emitter 40 of the second transistor is connected to wife 24 by a wife 41. The collector 42 of transistor 32 and the collector 44 of tran&gt; sistor 39 are connected by a wire 45 which m turn is connected to . ground by wire 46. A resistor 47 is connected across wires 30 and 36, as shown, to inflate conduction of the transistor. The magneto and the circuit associated therewith, which has been described -above, i functions as follows: Assume that the rotor 13 is in such position relative to core 14-that the flux through the cofe 14 has reached a positive maximum and lias started to decrease. Assume also that the parts are so disposed that such action causes the wire 22 to be slightly positive. This makes emitter 34 of transistor 3'2 positive with respect to the base 31 of such transistor by reason of the connection between them made up of wire 30, resistor 47, wire 36, winding 27, wire 24, winding 11, and wires 22 and 35. As a result, a current flows from emitter 34 to base 31, thereby turning transistor 32 bn, that is, lowering the resistance between its emitter and the collector. Therefore, increased current now flows from the emitter to the collector 42 of transistor 32, through the collector 44. to base 37 of transistor 39 through coil 27 and through winding '11. By transformer feedback action in coil 26 the rising current flow through winding 27 of such coil causes a current flow in winding 25, thus further increasing the base drive of transistor 32, still further causing . the circuit across primary winding 11 of the magneto to approach short circuited condition. The circuit remains in this virtually short circuited state as long as the current flow through it is increasing. When such current reaches its peak value, the base drive voltage of winding 25 of coil 26 reverses its polarity, thereby causing transistor 32 to turn off. This interrupts the current flowing through primary winding 11, thereby inducing a voltage in secondary winding 12. It will be seen that during this . portion of the operating cycle, transistor 39 remains nonconductive between emitted 40 and collector 44.

The operation of the circuit in the other half-cycle is the same, except that transistor 39 is then operative and transistor 32 is inoperative so far as high gain transistor . action is concerned. Such half-cycle starts when the rotor flux through the core. 14 has passed through the negative maximum and has started to increase in absolute value, causing the wire 24 to be slightly positive. This makes

3,229,162 the emitter 40 of transistor 39 positive with respect to its base 37 through winding 25 and resistor 47. This emitter to base current causes transistor 39 to turn on, that is, its emitter to collector resistance is lowered. Therefore, increased current flows through the emitter to the collector of transistor 39 and through winding 25 via transistor 32. The transformer feedback action between windings 25 and 27 causes the base drive of transistor 39 to increase, still further causing the circuit across primary winding 11 to approach a short circuited state. Such circuit stays in this state as long as the current through primary winding 11 is increasing. When the current reaches its peak value, the base drive voltage of winding 27 reverses its polarity, thereby causing transistor 39 to turn off. This interrupts the primary current through winding 11, resulting in high secondary voltage output from winding 12, as before.

It will be seen from the above that should it be desired to utilize only one-half of the flux reversals through core 14, one of the transistors 32 and 39 may be omitted. Thus if a circuit were desired which would yield secondary discharges on only the half-cycles first described above, transistor 39 would then be omitted along with the wires leading to its base, collector, and emitter, wire 36 being connected to ground.

Although only one embodiment of the invention has been illustrated in the accompanying drawing and described in the foregoing specification, it is to be especially understood that various changes, such as in the relative dimensions of the parts, materials used, and the like, as well as the suggested manner of use of the apparatus of the invention, may be made therein without departing from the spirit and scope of the invention as will now be apparent to those skilled in the art. Variations can be made in the saturation characteristics of the transformer 26 which will govern the electrical performance of the complete circuit. Thus although the cutting off of current flow in the primary of the magneto coil has been described as taking place at the peak of the current through primary winding 11 of the magneto coil, the transformer 26 can be designed so that such current ₄₀through primary 11 of the magneto coil is cut off when such primary current is at a desired predetermined value below such peak value. In such modification of the circuit described immediately above, the core 29 of transformer 26 is made so that its becomes saturated at the desired predetermined value below the peak value of the current through primary coil 11.