Patent ID: 7624718

Claim:
An engine control system comprising: an ion current measuring unit arranged to measure a negative ion current in a combustion chamber of an engine; a crank-angle measuring unit arranged to measure an engine crank angle; and a controller comprising: means for determining a first crank angle based on the negative ion current measured by the ion current measuring unit and the engine crank angle measured by the crank-angle measuring unit, the first crank angle being a crank angle corresponding to a rising point of the negative ion current at or above a first specified value on a negative ion current curve indicative of variations in negative ion current relative to crank angles; means for determining a second crank angle based on the negative ion current measured by the ion current measuring unit and the engine crank angle measured by the crank-angle measuring unit, the second crank angle being a crank angle corresponding to a peak point of the negative ion current on the negative ion current curve; means for calculating a substantial middle point between the first crank angle and the second crank angle as a third crank angle corresponding to a combustion center of gravity; and means for controlling an engine ignition timing so that the third crank angle approximates a desired target crank angle.