Variable flow turbocharger

1. A variable-flow turbocharger comprising:

a turbine housing defining a turbine chamber having an internal diameter;

a turbine wheel mounted within the turbine chamber for rotation about an axis;

an inlet passageway for introducing exhaust gas into the turbine chamber;

an outlet passageway for discharging the exhaust gas from the turbine chamber;

wherein the turbine chamber is defined collectively by an outer wall and an inner wall, wherein the outer wall and the inner wall are overlapping with the outer wall located radially outward of the inner wall, and an open space is defined between a radially outer surface of the inner wall and a radially inner surface of the outer wall, the open space being in fluid communication with the outlet passageway;

at least the inner wall being axially movable relative to the turbine wheel from a closed position to an open position;

wherein in the closed position of the inner wall, the internal diameter of the turbine chamber at an outlet side of the turbine wheel is defined by the inner wall such that the turbine chamber has a relatively small internal diameter at the outlet side of the turbine wheel, and wherein the inner wall in the closed position engages a portion of the outer wall so as to close off the open space and prevent exhaust gas from flowing through the open space; and

wherein in the open position of the inner wall, an axial spacing of the inner wall from the turbine wheel is increased such that the internal diameter of the turbine chamber at the outlet side of the turbine wheel is defined by the outer wall and is thereby increased, and wherein the inner wall in the open position uncovers the open space such that exhaust gas that has passed through the turbine wheel flows through the open space to the outlet passageway.

2. The variable-flow turbocharger of claim 1 , wherein the inner wall is configured and arranged such that moving the inner wall from the closed position to the open position causes a size of a throat area of the turbine to be increased.

3. The variable-flow turbocharger of claim 1 , wherein the outer wall is fixed.

4. The variable-flow turbocharger of claim 1 , wherein the inner wall is movable continuously between the closed position and the open position.

5. The variable-flow turbocharger of claim 1 , wherein the inner wall is movable in stepwise fashion between the closed position and the open position.

6. The variable-flow turbocharger of claim 1 , wherein the outer wall is also axially movable relative to the turbine wheel from a closed position to an open position and, once the inner wall has been moved at least partway toward the open position of the inner wall, the outer wall is then movable toward the open position of the outer wall.

7. The variable-flow turbocharger of claim 6 , wherein the outer and inner walls are arranged relative to each other such that motive force for moving the outer wall is provided by movement of the inner wall, and such that the outer wall remains stationary for part of a range of movement of the inner wall from the closed position to the open position of the inner wall, and when the inner wall reaches the end of said range, further movement of the inner wall causes the outer wall to move along with the inner wall.

8. The variable-flow turbocharger of claim 6 , wherein the outer wall extends to a position adjacent the inlet passageway when the outer wall is in the closed position thereof.

9. The variable-flow turbocharger of claim 8 , wherein the inlet passageway is defined in part by the outer wall such that when the outer wall is moved toward the open position thereof the inlet passageway becomes larger.

10. The variable-flow turbocharger of claim 1 , wherein the outer and inner walls are shaped to conform with an outer contour of the turbine wheel.

11. The variable-flow turbocharger of claim 10 , wherein the turbine wheel's outer contour has a decreasing diameter with respect to axial distance from an inlet side to the outlet side of the turbine wheel.

12. The variable-flow turbocharger of claim 10 , wherein an axially extending portion of the turbine wheel's outer contour from an inlet side of the turbine wheel partway toward the outlet side has a decreasing diameter with respect to axial distance, and a remaining axially extending portion of the outer contour up to the outlet side has a constant diameter with respect to axial distance.

13. The variable-flow turbocharger of claim 10 , wherein the turbine wheel's outer contour has a substantially constant diameter with respect to axial distance from an inlet side to the outlet side of the turbine wheel.

14. The variable-flow turbocharger of claim 1 , wherein the outer wall is fixed and is arranged to face an uncovered part of the turbine wheel that is covered by the inner wall when the inner wall is in the closed position and that is uncovered when the inner wall is moved to a position distant from the turbine wheel.

15. The variable-flow turbocharger of claim 1 , wherein the inlet passageway is defined between the outer wall and an opposite fixed wall of the turbine housing, and the inlet passageway remains unchanged in size when the inner wall is moved from the closed position to the open position.