Patent ID: 8123470

Claim:
A turbine assembly for a turbocharger, comprising: a turbine housing defining a bore extending along an axial direction and defining a chamber surrounding the bore for receiving exhaust gas, the chamber being open to the bore at a radially inner side of the chamber; a first-stage nozzle comprising a first nozzle ring mounted in the turbine housing and a plurality of circumferentially spaced first vanes each having a first end connected to the first nozzle ring and each extending generally parallel to the axial direction from the first end to an opposite second end; a second-stage nozzle comprising a second nozzle ring connected to the second ends of the first vanes and a plurality of circumferentially spaced second vanes each having a first end connected to the second nozzle ring and each extending generally parallel to the axial direction from the first end to an opposite second end, wherein the second nozzle ring divides only part of the second end of each first vane from part of the first end of each second vane; and a tubular piston disposed in the bore of the turbine housing, the piston being axially slidable relative to the turbine housing along the radially inner side of the chamber such that the piston blocks a variable portion of an axial length of the second-stage nozzle depending on axial position of the piston, the piston in a closed position thereof substantially closing the second-stage nozzle while the first-stage nozzle remains open such that exhaust gas flows to the turbine wheel via the first-stage nozzle, the piston in non-closed positions permitting flow through the second-stage nozzle.