Misfire determination system and method for internal combustion engine, vehicle including misfire determination system for internal combustion engine, and system for and method of estimating rigidity of torsion element

A torsion-element rigidity estimation system for estimating a rigidity of a torsion element that is interposed between an output shaft of a multi-cylinder internal combustion engine and a downstream shaft, the system comprising:

• an output-shaft rotational speed detection section that detects an output shaft rotational speed that is the rotational speed of the output shaft;
• a downstream shaft rotational speed detection section that detects a downstream shaft rotational speed that is the rotational speed of the downstream shaft;
• a rigidity estimation section that extracts a frequency component caused by a resonance due to torsion of the torsion element from the detected output shaft rotational speed, extracts a frequency component caused by the resonance from the detected downstream shaft rotational speed, and estimates the rigidity of the torsion element based on a value obtained by comparing amplitudes of both of the extracted frequency components and on the detected output shaft rotational speed.

An internal-combustion-engine misfire determination method of determining an occurrence of a misfire in a multi-cylinder internal combustion engine, of which an output shaft is connected, through a torsion element, to a downstream shaft downstream of the torsion element, the misfire determination method comprising:

• extracting a frequency component caused by a resonance due to torsion of the torsion element from an output shaft rotational speed that is the rotational speed of the output shaft, extracting a frequency component caused by the resonance from a downstream shaft rotational speed that is the rotational speed of the downstream shaft, and estimating a rigidity of the torsion element based on a value obtained by comparing amplitudes of both of the extracted frequency components and on the output shaft rotational speed;
• calculating a resonance influence component caused by an influence of a resonance on the output shaft rotational speed, based on the estimated rigidity of the torsion element, the output shaft rotational speed and the downstream shaft rotational speed, and
• determining the occurrence of the misfire in the internal combustion engine based on a rotational speed for determination that is obtained by subtracting the calculated resonance influence component from the output shaft rotational speed.

A torsion-element rigidity estimation method of estimating a rigidity of a torsion element that is interposed between an output shaft of a multi-cylinder internal combustion engine and a downstream shaft, the method comprising:

• extracting a frequency component caused by a resonance due to torsion of the torsion element from an output shaft rotational speed that is the rotational speed of the output shaft, and extracting a frequency component caused by the resonance from a downstream shaft rotational speed that is the rotational speed of the downstream shaft;
• and
• estimating the rigidity of the torsion element based on a value obtained by comparing amplitudes of both of the extracted frequency components and on the output shaft rotational speed.