Method of Controlling a Turbocharger Having a Variable-Geometry Mechanism and a Waste Gate

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.