A method for controlling a variable-geometry
turbine (24) that includes a variable-geometry mechanism that is movable between a fully closed position closing a relatively greater portion of the
turbine nozzle and a fully open position closing a relatively smaller portion of the
nozzle. The
turbine (24) further comprises a waste gate (40) movable between a closed position and an open position in which some of the
exhaust gas bypasses the turbine (24). At low engine speeds,
turbocharger boost us regulated by regulating the position of the
wastegate. At high engine speeds, the
variable geometry is fully open and the
wastegate is opened again. When at medium engine speeds, the
variable geometry mechanism is to be moved from its closed position toward its fully open position, the waste gate (40) is in an open position to cause a proportion of the
exhaust gas to bypass the turbine (24) and thereby reduce the pressure of the
exhaust gas in the chamber. While this reduced pressure of the exhaust gas is in effect, the variable-geometry mechanism is moved from the fully closed position toward the fully open position while simultaneously the waste gate begins to close.