Magneto ignition system for an internal combustion engine

Claim 1

In a magneto ignition system for an internal combustion engine having a magnet (11) rotating with the engine; a magneto armature (12) in magnetically coupled relation to the rotating magnet and having a primary coil (13a) connected to a primary circuit, and a secondary coil (13b) connected to a spark plug (15); a semiconductor switch (16) having a control path (base-emitter) connected in the primary circuit; a control circuit (20-25) connected to the control path of the semiconductor switch (16) and to the primary circuit of the ignition coil, including means (22) sensing the voltage level across said primary circuit, and connection means (20, 21) responsive to said voltage level connected to and controlling conduction and cut-off, respectively, of the semiconductor switch as a function of said voltage level to provide, upon conduction of the semiconductor switch, for current flow through the primary coil, and sudden interruption of current flow upon cut-off and to generate a spark in said spark plug at a predetermined angular position with respect to top dead center (TDC) position of a piston of the engine, means to advance the spark upon increase of speed of the engine comprising means (28, 29, 30) modifying the voltage level across said primary circuit as a function of increasing speed of the engine in a direction to cause response of said voltage level sensing means, and hence of said connection means to control said semiconductor switch (16) to cut off at an advanced angular position with respect to TDC position of a piston of the engine, said modifying means comprising a frequency responsive circuit (28, 29, 30) connected to the primary circuit and providing an output changing the voltage level in said primary circuit as a function of change of frequency of the current flow in the primary circuit upon change of speed of rotation of the magnet as the speed of the engine changes.