Knocking detection method, ignition timing control method, and ignition timing control system

An ignition timing control method of controlling an ignition timing of ignition of air-fuel mixture in a combustion chamber of an internal combustion engine, comprising:

• a detection step of detecting presence or absence of occurrence of knocking in each combustion cycle for the ignition timing which is currently set;
• a correlation update step of calculating a variation trend, up to a present time, of a knocking occurrence frequency on the basis of a result of detection of the presence or absence of occurrence of knocking, and updating a correlation between a change in the ignition timing and the knocking occurrence frequency to a latest state;
• and
• an ignition timing control step of controlling the ignition timing of the internal combustion engine on the basis of the correlation,
• wherein the detection step includes:
• obtaining an oscillation waveform which is generated by combustion of air-fuel mixture in the combustion chamber;
• setting a first time window preceding a maximum inner pressure time at which an inner pressure of the combustion chamber is at maximum in a single combustion cycle and a second time window immediately after the maximum inner pressure time, and transforming each of a first waveform portion included in the first time window and a second waveform portion included in the second time window into an expression-domain expression, of the oscillation waveform;
• and
• setting a first frequency window and a second frequency window, extracting a first representative value which is a representative value of the frequency domain expression of the first waveform portion in the first frequency window and a second representative value which is a representative value of the frequency domain expression of the second waveform portion in the second frequency window, and determining whether knocking has occurred on the basis of a relationship between the second representative value and the first representative value.

A control system configured to control an ignition timing of ignition of air-fuel mixture in a combustion chamber of an internal combustion engine, comprising:

• a knocking detection part configured to detect presence or absence of occurrence of knocking in each combustion cycle for the ignition timing which is currently set;
• a correlation update part configured to calculate a variation trend, up to a present time, of a knocking occurrence frequency on the basis of a result of detection of the presence or absence of occurrence of knocking, and updating a correlation between a change in the ignition timing and the knocking occurrence frequency to a latest state;
• an optimum ignition timing calculation part configured to determine an optimum ignition timing of the internal combustion engine on the basis of the correlation, and
• an ignition timing control part configured to control the ignition timing by using the optimum ignition timing determined by the optimum ignition timing calculation part as a control target value,
• wherein the knocking detection part includes:
• an oscillation waveform acquisition part configured to obtain an oscillation waveform which is generated by combustion of air-fuel mixture in the combustion chamber;
• a time-frequency transform part configured to set a first time window preceding a maximum inner pressure time at which an inner pressure of the combustion chamber is at maximum in a single combustion cycle and a second time window immediately after the maximum inner pressure time, and transform each of a first waveform portion included in the first time window and a second waveform portion included in the second time window into an expression-domain expression, of the oscillation waveform;
• and
• a knocking determination part configured to set a first frequency window and a second frequency window, extract a first representative value which is a representative value of the frequency domain expression of the first waveform portion in the first frequency window and a second representative value which is a representative value of the frequency domain expression of the second waveform portion in the second frequency window, and determine whether knocking has occurred on the basis of a relationship between the second representative value and the first representative value.