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A turbocharger having a turbine housing defining a chamber for receiving exhaust gas, and a nozzle leading from the chamber. Exhaust gas flows from the nozzle through a turbine wheel in the chamber and changes direction from a radially inward direction in the nozzle to an axial direction downstream

A turbocharger having a turbine housing defining a chamber for receiving exhaust gas, and a nozzle leading from the chamber. Exhaust gas flows from the nozzle through a turbine wheel in the chamber and changes direction from a radially inward direction in the nozzle to an axial direction downstream of the turbine wheel. A divider in the nozzle divides the nozzle into first-stage and second-stage nozzles. The divider has an upstream surface to guide exhaust gas through the first-stage nozzle and an opposite downstream surface to guide exhaust gas flowing through the second-stage nozzle. An axially slidable tubular piston, disposed in the turbine housing, has a radially inner surface extending along the axial direction and a non-flat upstream end surface. The piston also includes a curved flow-guiding surface causing the exhaust gas to change direction. In a closed position, the piston abuts the divider to close the second-stage nozzle.

대표청구항 ▼

That which is claimed: 1. A method for regulating exhaust gas flow to a turbocharger comprising: providing a turbine housing defining a bore extending along a downstream axial direction and defining a chamber surrounding the bore for receiving exhaust gas, and a nozzle leading from the chamber gene

That which is claimed: 1. A method for regulating exhaust gas flow to a turbocharger comprising: providing a turbine housing defining a bore extending along a downstream axial direction and defining a chamber surrounding the bore for receiving exhaust gas, and a nozzle leading from the chamber generally radially inwardly into the bore; providing a turbine wheel rotatably mounted in the bore and comprising a hub and a plurality of turbine blades extending generally radially outwardly from the hub and terminating in blade tips; providing a generally ring-shaped divider in the nozzle that divides the nozzle into a first-stage nozzle and a second-stage nozzle, the first-stage nozzle being delimited between a fixed member of the turbine assembly and the divider, the divider having an upstream surface guiding exhaust gas flowing through the first-stage nozzle and an opposite downstream surface guiding exhaust gas flowing through the second-stage nozzle, the divider having a radially innermost edge, the first-stage nozzle and second-stage nozzle each receiving exhaust gas from the chamber and each directing the exhaust gas radially inwardly onto the blade tips of the turbine wheel; providing a tubular piston disposed in the bore of the turbine housing and being axially slidable therein, the piston having a radially inner surface extending along the axial direction and having a non-flat upstream end surface, with a first radius, that includes a contact region for contacting a portion of the divider with the piston in a closed position so as to substantially close the second-stage nozzle, and movement of the piston in the downstream axial direction opening the second-stage nozzle; and configuring the piston to include a curved flow-guiding surface with a second radius proceeding from the contact region to the inner surface, the flow-guiding surface turning from a generally radially inward direction to the downstream axial direction so as to assist in causing the exhaust gas to execute said change in direction, wherein the blade tips define a contour, in a radial-axial projection, having a portion generally aligned with the second-stage nozzle that is concave in a radially outward direction, and the curved flow-guiding surface of the piston is generally complementary and parallel to said portion of the contour of the blade tips. 2. The method for producing a turbocharger of claim 1, wherein the upstream surface of the divider defines a convex surface generally projecting in an upstream direction of the bore. 3. The method for producing a turbocharger of claim 1, wherein the downstream surface of the divider defines a concave surface generally projecting in a downstream direction of the bore. 4. The method for producing a turbocharger of claim 1, wherein the radially innermost edge of the divider defines a convex surface generally projecting in a radial direction of the bore. 5. The method for producing a turbocharger of claim 1, wherein the non-flat upstream end surface of the piston defines a convex surface generally projecting in an upstream direction of the bore. 6. The method for producing a turbocharger of claim 1, wherein the curved flow-guiding surface of the piston defines a convex surface. 7. The method for producing a turbocharger of claim 1, wherein the upstream and downstream surfaces of the divider are configured to direct a flow of exhaust gas to the turbine wheel in an advantageous direction. 8. The method for producing a turbocharger of claim 1, wherein the downstream surface of the divider defines a concave surface generally projecting in a downstream direction of the bore, wherein the non-flat upstream end surface of the piston defines a convex surface generally projecting in an upstream direction of the bore. 9. The method for producing a turbocharger of claim 1, wherein the downstream surface of the divider defines a concave surface generally projecting in an downstream direction of the bore, wherein the radially innermost edge of the divider defines a convex surface generally projecting in a radial direction of the bore, wherein the non-flat upstream end surface of the piston defines a convex surface generally projecting in an upstream direction of the bore, and wherein the curved flow-guiding surface of the piston defines a convex surface. 10. A turbine assembly for a turbocharger, comprising: a turbine housing defining a bore extending along a downstream axial direction and defining a chamber surrounding the bore for receiving exhaust gas, and a nozzle leading from the chamber generally radially inwardly into the bore; a turbine wheel rotatably mounted in the bore and comprising a hub and a plurality of turbine blades extending generally radially outwardly from the hub and terminating in blade tips, the hub of the turbine wheel and the bore of the turbine housing being configured such that exhaust gas flowing from the nozzle to and through the turbine wheel undergoes a change in direction from a generally radially inward direction in the nozzle to the downstream axial direction downstream of the turbine wheel; a generally ring-shaped divider in the nozzle dividing the nozzle into a first-stage nozzle and a second-stage nozzle, the first-stage nozzle being delimited between a fixed member of the turbine assembly and the divider, the divider having an upstream surface guiding exhaust gas flowing through the first-stage nozzle and an opposite downstream surface guiding exhaust gas flowing through the second-stage nozzle, the divider having a radially innermost edge; the first-stage nozzle and second-stage nozzle each receiving exhaust gas from the chamber and each directing the exhaust gas radially inwardly onto the blade tips of the turbine wheel; wherein the blade tips define a contour, in a radial-axial projection, having a portion generally aligned with the second-stage nozzle that is concave in a radially outward direction; and a tubular piston disposed in the bore of the turbine housing and being axially slidable therein, the piston having a radially inner surface extending along the axial direction and having a non-flat upstream end surface, with a first radius, that includes a contact region for contacting a portion of the divider with the piston in a closed position so as to substantially close the second-stage nozzle, and movement of the piston in the downstream axial direction opening the second-stage nozzle, wherein the piston includes a curved flow-guiding surface with a second radius proceeding from the contact region to the inner surface, the flow-guiding surface turning from a generally radially inward direction to the downstream axial direction so as to assist in causing the exhaust gas to execute said change in direction, and wherein the curved flow-guiding surface of the piston is generally complementary and parallel to said portion of the contour of the blade tips that is generally aligned with the second-stage nozzle. 11. The turbocharger of claim 10, wherein the upstream surface of the divider defines a convex surface generally projecting in an upstream direction of the bore. 12. The turbocharger of claim 10, wherein the downstream surface of the divider defines a concave surface generally projecting in a downstream direction of the bore. 13. The turbocharger of claim 10, wherein the radially innermost edge of the divider defines a convex surface generally projecting in a radial direction of the bore. 14. The turbocharger of claim 10, wherein the non-flat upstream end surface of the piston defines a convex surface generally projecting in an upstream direction of the bore. 15. The turbocharger of claim 10, wherein the curved flow-guiding surface of the piston defines a convex surface. 16. The turbocharger of claim 10, wherein the upstream and downstream surfaces of the divider are configured to direct a flow of exhaust gas to a turbine wheel in an advantageous direction. 17. The turbocharger of claim 10, wherein the downstream surface of the divider defines a concave surface generally projecting in a downstream direction of the bore, wherein the non-flat upstream end surface of the piston defines a convex surface generally projecting in an upstream direction of the bore. 18. The turbocharger of claim 10, wherein the downstream surface of the divider defines a concave surface generally projecting in an downstream direction of the bore, wherein the radially innermost edge of the divider defines a convex surface generally projecting in a radial direction of the bore, wherein the non-flat upstream end surface of the piston defines a convex surface generally projecting in an upstream direction of the bore, and wherein the curved flow-guiding surface of the piston defines a convex surface. 19. A system for a turbocharger comprising: a turbine housing defining a bore extending along a downstream axial direction and defining a chamber surrounding the bore for receiving exhaust gas, and a nozzle leading from the chamber generally radially inwardly into the bore; a turbine wheel rotatably mounted in the bore and comprising a hub and a plurality of turbine blades extending generally radially outwardly from the hub and terminating in blade tips, the hub of the turbine wheel and the bore of the turbine housing being configured such that exhaust gas flowing from the nozzle to and through the turbine wheel undergoes a change in direction from a generally radially inward direction in the nozzle to the downstream axial direction downstream of the turbine wheel; a generally ring-shaped divider in the nozzle dividing the nozzle into a first-stage nozzle and a second-stage nozzle, the first-stage nozzle being delimited between a fixed member of the turbine assembly and the divider, the divider having an upstream surface guiding exhaust gas flowing through the first-stage nozzle and an opposite downstream surface guiding exhaust gas flowing through the second-stage nozzle, the divider having a radially innermost edge; the first-stage nozzle and second-stage nozzle each receiving exhaust gas from the chamber and each directing the exhaust gas radially inwardly onto the blade tips of the turbine wheel; and a tubular piston disposed in the bore of the turbine housing and being axially slidable therein, the piston having a radially inner surface extending along the axial direction and having a non-flat upstream end surface, with a first radius, that includes a contact region for contacting a portion of the divider with the piston in a closed position so as to substantially close the second-stage nozzle, and movement of the piston in the downstream axial direction opening the second-stage nozzle, wherein the piston includes a curved flow-guiding surface with a second radius proceeding from the contact region to the inner surface, the flow-guiding surface turning from a generally radially inward direction to the downstream axial direction so as to assist in causing the exhaust gas to execute said change in direction, wherein the blade tips define a contour, in a radial-axial projection, having a portion generally aligned with the second-stage nozzle that is concave in a radially outward direction, and the curved flow-guiding surface of the piston is generally complementary and parallel to said portion of the contour of the blade tips. 20. The system for a turbocharger of claim 19, wherein the upstream surface of the divider defines a convex surface generally projecting in an upstream direction of the bore. 21. The system for a turbocharger of claim 19, wherein the downstream surface of the divider defines a concave surface generally projecting in a downstream direction of the bore. 22. The system for a turbocharger of claim 19, wherein the radially innermost edge of the divider defines a convex surface generally projecting in a radial direction of the bore. 23. The system for a turbocharger of claim 19, wherein the non-flat upstream end surface of the piston defines a convex surface generally projecting in an upstream direction of the bore. 24. The system for a turbocharger of claim 19, wherein the curved flow-guiding surface of the piston defines a convex surface. 25. The system for a turbocharger of claim 19, wherein the upstream and downstream surfaces of the divider are configured to direct a flow of exhaust gas to a turbine wheel in an advantageous direction. 26. The system for a turbocharger of claim 19, wherein the downstream surface of the divider defines a concave surface generally projecting in a downstream direction of the bore, wherein the non-flat upstream end surface of the piston defines a convex surface generally projecting in an upstream direction of the bore. 27. The system for a turbocharger of claim 19, wherein the downstream surface of the divider defines a concave surface generally projecting in an downstream direction of the bore, wherein the radially innermost edge of the divider defines a convex surface generally projecting in a radial direction of the bore, wherein the non-flat upstream end surface of the piston defines a convex surface generally projecting in an upstream direction of the bore, and wherein the curved flow-guiding surface of the piston defines a convex surface.