Abstract: A turbocharger having a variable nozzle with stepped two-stage vanes (50), the variable nozzle comprising a tubular piston (70) disposed in the bore (44) of the turbine housing (38) such that the piston (70) is axially slidable adjacent to the vanes (50) that extend across the nozzle. Each vane defines a first vane stage (50a) proximate the free end of the vane, the second vane stage (50b) having a different aerodynamic contour in comparison with the first vane stage (50a), each vane comprising a step (60) transitioning from the first vane stage (50a) to the second vane stage (50b). The piston (70) in a closed position closes the second vane stage (50b) so that exhaust gas flows only through the first vane stage (50a). The second vane stage (50b) is progressively opened as the piston (70) is axially slid toward an open position.

Abstract: 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.

Abstract: A turbocharger having a variable nozzle with stepped two-stage vanes (50), the variable nozzle comprising a tubular piston (70) disposed in the bore (44) of the turbine housing (38) such that the piston (70) is axially slidable adjacent to the vanes (50) that extend across the nozzle. Each vane defines a first vane stage (50a) proximate the free end of the vane, the second vane stage (50b) having a different aerodynamic contour in comparison with the first vane stage (50a), each vane comprising a step (60) transitioning from the first vane stage (50a) to the second vane stage (50b). The piston (70) in a closed position closes the second vane stage (50b) so that exhaust gas flows only through the first vane stage (50a). The second vane stage (50b) is progressively opened as the piston (70) is axially slid toward an open position.

Abstract: 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.