Patent ID: 8112994

Claim:
A method for controlling a variable-geometry turbocharger having a turbine comprising a turbine wheel mounted for rotation in a turbine housing, the turbine housing defining a chamber surrounding the turbine wheel for receiving exhaust gas from an engine and further defining a nozzle leading from the chamber generally radially inwardly to the turbine wheel through which exhaust gas flows from the chamber to the turbine wheel, the turbine including a variable-geometry mechanism that is movable to regulate flow through the nozzle, the turbine further comprising a waste gate movable between a closed position in which substantially all of the exhaust gas is directed from the engine through the turbine nozzle to the turbine wheel and a plurality of open positions differing from one another in degrees of openness for allowing a variable proportion of the exhaust gas to bypass the turbine, the method comprising the steps of: at engine speeds below a predetermined first speed N 1 , maintaining the variable-geometry mechanism in a relatively closed position and regulating boost of the turbocharger by regulating the position of the waste gate; at intermediate engine speeds between the first speed N 1 and a higher predetermined second speed N 2 , maintaining the waste gate in a relatively closed position and regulating boost by regulating the position of the variable-geometry mechanism; and at engine speeds above N 2 , maintaining the variable-geometry mechanism in a relatively open position and regulating boost by regulating the position of the waste gate.