Method and system for detecting a crank angle of an engine

A system for detecting a crank angle of an engine, comprising

• a crank pulse rotor coupled with a crankshaft of the engine, said crank pulse rotor comprising a non-toothed portion formed by removing at least one of a plurality of teeth formed consecutively at predetermined intervals on an outer circumference of the crank pulse rotor;
• the teeth consecutively formed on the crank pulse rotor arranged in a range including a position corresponding to top dead center position of a piston of the engine;
• a crank angle sensor arranged at a position facing the outer circumference of the crank pulse rotor;
• an interval calculating unit for measuring time intervals between adjacent ones of the teeth based on sensing signals of the teeth detected by the crank angle sensor during rotation of the crankshaft;
• a ratio calculating unit operable to divide a last value of the time interval by a second-to last value of the time interval to calculate a ratio of crank pulse intervals;
• and
• a maximum ratio detecting unit for comparing a current crank pulse ratio with an immediately preceding ratio and retaining a larger ratio value selected from said current crank pulse ratio and said immediately preceding current crank pulse ratio;
• and for determining presence of the non-toothed portion when the ratio of the crank pulse intervals calculated is the maximum ratio within a cycle of the engine.

A method of detecting a presence of a non-toothed portion of a crank pulse rotor coupled with a crankshaft of a 4-cycle, single-cylinder engine, said crank pulse rotor comprising a toothed portion having a plurality of teeth consecutively formed at predetermined intervals on an outer circumference thereof;

• said teeth being arranged in a range including a position corresponding to a top dead center position of a piston of the engine;
• said method comprising the steps of:
• (a) measuring crank pulse time intervals between adjacent teeth of said crank pulse rotor during rotation of the crankshaft;
• (b) storing two successive crank pulse time intervals;
• (c) calculating crank pulse time interval ratios by dividing a last value of the crank pulse time interval by a second-to last value of the crank pulse time interval;
• (d) comparing a current crank pulse ratio with an immediately preceding crank pulse ratio;
• (e) retaining a larger ratio value selected from said current pulse ratio and said immediately preceding crank pulse ratio;
• (f) repeating the method steps (b) through (e) for a cycle of the engine;
• and
• (g) determining a presence of the non-toothed portion when the ratio of the crank pulse intervals calculated is the maximum ratio within said cycle of the engine.