Engine natural vibration frequency detection method, active vibration isolation support device control method, engine natural vibration frequency detection apparatus, active vibration isolation support device control apparatus, active vibration isolation support device, and vibration frequency detection apparatus for vibrating body

The natural vibration frequency of a roll resonance which does not occur since the engine rotation number is high in a normal operation range of an engine is detected at the time of engine start or stop when the engine rotation number is lower than the normal operation range, and thus the natural vibration frequency of the roil resonance can be detected with a good accuracy. A current is generated by an electromotive force of an actuator of the active vibration isolation support device excited by the engine immediately before stopping its rotation, and the frequency of the current is used to detect the natural vibration frequency of the engine, and the roll resonance of the engine is suppressed by controlling the operation of the active vibration isolation support device at the time of engine start based on the natural vibration frequency, thereby not only eliminating the need of a specific frequency detection sensor, but also effectively reducing the vibration at the time of engine start when the roll resonance becomes strong.