Super charger (turbocharger) of an internal combustion engine which has electric assist facility is known as disclosed by Japanese Patent Laid-Open No. 2003-239755, conventionally. The above mentioned prior supercharger further has a movable nozzle (VN) for changing flow velocity of exhaust gas which flows through a turbine.
As for an internal combustion engine comprising a turbocharger, a problem of so-called turbo lag occurs in a low revolution region. According to the above mentioned prior supercharger, it is possible to restrain the turbo lag from occurring by assisting the revolution of the supercharger by the electric motor in a low revolution region. According to this supercharger, the occurring of the turbo lag can be also restrained by closing the VN in a low revolution region.
More particularly, the above mentioned prior system equipped with the supercharger implements the supercharging by controlling the VN in a feedback manner while using the assist by the electric motor during a period in which a true boost pressure is low enough for a target boost pressure under a condition in which an acceleration of the internal combustion engine is required. Afterwards, when the true boost pressure gets closer to the target boost pressure, the assist by the electric motor is stopped so as to implement the target boost pressure only by the feedback control of the VN. According to such operation, the turbo lag can be controlled effectively while restraining the electric consumption by the electric motor.    Patent Document 1: Japanese Patent Laid-open No. 2003-239755    Patent Document 2: Japanese Patent Laid-open Hei5-280365    Patent Document 3: Japanese Patent Laid-open Hei5-280363