Engine crank angle detecting device

A crank angle detecting device for an engine, comprising:

• a ring gear fixed to a crankshaft of a single cylinder engine, the ring gear having a plurality of teeth as well as a toothless portion formed around an outer periphery at equal intervals;
• and
• a crank angle sensor for detecting the plurality of teeth formed on the ring gear, the crank angle sensor detecting a lateral length of each of the plurality of teeth as well as an interval of two adjacent teeth and calculating a ratio therebetween to distinguish the toothless portion from the teeth,
• wherein the crank angle sensor and the toothless portion formed on the ring gear are so positioned that the toothless portion is detected when a piston is close to a bottom dead center position.

A method for detecting a crank angle, comprising:

• attaching a ring gear to a crank shaft of an engine with the ring gear having a plurality of projections formed around an outer periphery at equal intervals as well as an irregular interval portion;
• detecting a start and an end on both sides of each of the plurality of projections formed on the ring gear;
• detecting a lateral length of each of the plurality of projections and an interval of two adjacent projections, and calculating a ratio therebetween to distinguish the irregular interval portion from the plurality of projections;
• and
• positioning a crank angle sensor and the irregular interval portion so that the irregular interval portion is detected when a piston is close to a bottom dead center position.