Patent ID: 8639432

Claim:
A spark-ignition engine which is provided with a vibration sensor for detecting vibration of the engine, or an in-cylinder pressure sensor for detecting an in-cylinder pressure of the engine, and designed such that a spark timing of a spark plug is set on a retard side with respect to a compression top dead center, in a low engine speed/high engine load region and in a normal state where no abnormal combustion occurs, wherein: the spark-ignition engine comprises a controller operable to control the spark timing of the spark plug and accept information about a vibration intensity detected by the vibration sensor or information about an in-cylinder pressure detected by the in-cylinder pressure sensor; and the controller is operable: when a maximum value of the vibration intensity acquired from the vibration sensor or a maximum value of the in-cylinder pressure acquired from the in-cylinder pressure sensor, in the low engine speed/high engine load region, is equal to or greater than a given threshold value, to execute a control operation of shifting the spark timing of the spark plug from the point set in the normal state on the retard side with respect to the compression top dead center, farther toward the retard side; and when a post-spark retard maximum detection value is greater than a pre-spark retard maximum detection value, to determine that preignition occurs which is a phenomenon that an air-fuel mixture prematurely self-ignites, where: the post-spark retard maximum detection value is the maximum value of the vibration intensity or the maximum value of the in-cylinder pressure, which is acquired from the vibration sensor or the in-cylinder pressure sensor after the retard of the spark timing; and the pre-spark retard maximum detection value is the maximum value of the vibration intensity or the maximum value of the in-cylinder pressure, which is acquired before the retard of the spark timing.