Patent ID: 7171948

Claim:
An ignition device for an internal combustion engine, comprising: an exciter coil that is provided in a magneto AC generator rotating synchronously with the internal combustion engine and generates once for every one rotation of a crankshaft of the engine in forward rotation of the internal combustion engine, an AC voltage having a positive half-wave voltage and first and second negative half-wave voltages present before and after the positive half-wave voltage, respectively; an ignition capacitor that is provided in a primary side of an ignition coil and is charged in one polarity with the positive half-wave voltage; a discharge switch that is provided to turn on upon receiving an ignition signal and cause electric charges stored in the ignition capacitor to be discharged through a primary coil of the ignition coil; and a ignition control unit that supplies the ignition signal to the discharge switch at an ignition position of the internal combustion engine, wherein said ignition control unit comprises: ignition signal generating means that has an ignition timer for measuring ignition position detection time data and generates the ignition signal when the ignition timer completes the measurement of the ignition position detection time data; negative voltage generating position detecting means for detecting a generating position of the first negative half-wave voltage and a generating position of the second negative half-wave voltage; operation state determining means for determining whether the internal combustion engine is in a state of starting period or in a state after completion of starting operation; starting-period ignition controlling means for controlling the generating position of the ignition signal when the operation state determining means determines that the internal combustion engine is in a state of starting period; and steady-state-operation-period ignition controlling means for controlling the generating position of the ignition signal when the operation state determining means determines that the internal combustion engine is in a state of steady-state operation period, and wherein said starting-period ignition controlling means is comprised so as to, upon detection of the generating position of the second negative half-wave voltage, execute a process to arithmetically operate as the ignition position detection time data, time period Tigs that is required for the internal combustion engine to rotate from the generating position of the second negative half-wave voltage to an ignition position suitable in starting period, at the rotational speed of the internal combustion engine that is obtained from time period T 1 between detection of the generating position of the first negative half-wave voltage and detection of the generating position of the second negative half-wave voltage, and an angle from the generating position of the first negative half-wave voltage to the generating position of the second negative half-wave voltage.