The present invention provides a servo actuated operating mechanism for a coacting lobed rotor positive displacement supercharger combining a low cost and capacity electromagnetic clutch with a small oil pump internal to the supercharger unit. The oil pump supplies on demand oil pressure from oil in a hydraulic clutch housing or the supercharger timing gear case and acts as a servomechanism to actuate an internal hydraulic clutch. The hydraulic clutch can be engaged over a much wider range of speeds and loads than is possible with an electromagnetic clutch alone. The electro-hydraulic servomechanism provides improved highway fuel economy relative to an electromagnetic clutch as the engagement speed could be moved to a higher rotational speed (rpm). The internal hydraulic system makes higher supercharger engagement speeds possible with a hydraulic system, but without the assembly and leak issues associated with externally plumbed engine oil system actuated clutches.