Simplified automatic advance ignition system for an internal combustion engine

Claim 1

An ignition system for an internal combustion engine comprising: a magneto generator driven by the engine and having an ignition circuit armature and windings thereon wound in the form of a built-in spark coil comprising primary and secondary windings; at least one spark plug connected in circuit with said secondary winding; electronic circuit means, connected in parallel with at least part of said primary winding and including full wave rectifying means for rectifying the output voltage of said primary winding, said electronic circuit means including also the switching path of a semiconductor switch arranged in series with a similarly poled diode in a circuit branch substantially short-circuiting said primary winding through said rectifying means except when said semiconductor switch is turned off by a control pulse on a control electrode thereof, said electronic circuit means further including a transistor (226) responsive to the voltage across the combination of said switching path and said similarly poled diode for producing a control pulse and applying it to said control terminal of said semiconductor switch when said voltage exceeds a predetermined voltage, said transistor having its switching path connected in parallel to the control path of said semiconductor switch and having its control electrode connected to a voltage divider energized by the output of said rectifying means and further including a Zener diode (229) so connected that the control path of said transistor (226) is not energized until the output of said rectifying means overcomes the breakdown threshold of said Zener diode (229), and means for reducing the amplitude of the first of a succession of at least two voltage half waves produced in said primary winding as rectified by said rectifying means, relative to the second of said half waves, said amplitude reducing means including loading, by electrical resistance, of the half wave path of said rectifying means for said first voltage half wave, so that said first voltage half wave of said succession has a lower peak voltage than the immediately succeeding voltage half wave, whereby at low speeds of said engine, said shortcircuiting circuit branch is not interrupted during said first voltage half wave of said succession, but is interrupted by the second voltage half wave of said succession.