Importance

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Abstract

A magnet ignition device is provided with an angular position detecting device for producing a first angular signal with one polarity corresponding to an angular position of a given crankshaft of an engine and a second angular signal with the other polarity corresponding to an angular position of the crankshaft retarded by a given angle relative to the angular position where the first angular signal is generated. An ignition timing operation circuit is driven by the first angular signal. A signal representing advance angle information of the result of the operation by the operation circuit and the second angular signal are both applied to a switching element. In the circuit arrangement, only the second angular signal is used as an ignition signal in low rotational frequencies suffering from a great variation of the rotational frequency of the engine and, in high rotational frequencies higher than a given rotational frequency, only the advance angle signal is used as the ignition signal. With such an arrangement, an instability of the ignition timing due to a great variation of the rotational frequency in low rotational frequencies is prevented thereby to secure an accurate and stable ignition timing.

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First Claim