Device for controlling a variable geometry turbocharger

The present invention is an apparatus for controlling a variable geometry turbocharger (VGT) in closed loop and open loop modes, and a switching mechanism for determining whether open loop or closed loop control laws should be used. In the closed loop mode, a correction factor, obtained from a pressure correction map based on engine speed and atmospheric pressure, is subtracted from the desired boost pressure to prevent overspeed of the turbocharger at lower atmospheric pressures. The actual boost pressure is then compared to the desired boost pressure after correction to obtain a boost pressure error signal. The boost pressure error signal is used as an input to a proportional integral differential control law that responsively produces a desired VGT vane position. A minimum limit on the desired VGT vane position is based on engine speed and fuel quantity, whereas a maximum allowable vane position may be a predetermined constant or function. A linearization map is used to obtain a VGT current signal that is transmitted to an actuator for moving the vane position.