Variable nozzle mechanism and variable geometry turbocharger

1. A variable nozzle mechanism for a variable geometry turbocharger, comprising:

a first annular member;

a second annular member disposed so as to face the first annular member and forming an exhaust gas flow passage having an annular shape between the first annular member and the second annular member, for guiding exhaust gas to a turbine rotor of the turbo charger from a scroll flow passage formed on a radially outer side of the turbine rotor; and

a plurality of nozzle vanes supported rotatably on the first annular member and configured to be capable of adjusting a flow passage area of the exhaust gas flow passage,

wherein the first annular member has a plurality of support holes for supporting the plurality of nozzle vanes rotatably, the support holes being disposed at intervals in a circumferential direction of the turbine rotor,

wherein an inner peripheral edge of the first annular member includes a plurality of first inner edge portions belonging to an angular range in which the support holes exist in the circumferential direction of the turbine rotor and a plurality of second inner edge portions belonging to an angular range in which the support holes do not exist in the circumferential direction of the turbine rotor, and

wherein at least one second inner edge portion of the plurality of second inner edge portions comprises a recess portion recessed outward in a radial direction of the turbine rotor, the recess portion extending in an axial direction of the turbine rotor from a surface defining the exhaust gas flow passage.

2. The variable nozzle mechanism according to claim 1 ,

wherein the recess portion is formed at a center position of the angular range in which the support holes do not exist in the circumferential direction of the turbine rotor.

3. The variable nozzle mechanism according to claim 1 ,

wherein the recess portion is formed to have an arc shape as seen in the axial direction of the turbine rotor.

4. The variable nozzle mechanism according to claim 1 ,

wherein the recess portion is formed to have a linear shape as seen in the axial direction of the turbine rotor.

5. The variable nozzle mechanism according to claim 1 ,

wherein the inner peripheral edge has an annular protruding portion protruding inward in the radial direction of the turbine rotor, on the side of the exhaust gas flow passage, and

wherein the recess portion is formed on the annular protruding portion.

6. The variable nozzle mechanism according to claim 5 ,

wherein the recess portion is formed over a range of not less than 60% of a thickness of the annular protruding portion in the axial direction of the turbine rotor.

7. The variable nozzle mechanism according to claim 1 ,

wherein the recess portion is formed so as to penetrate through the first annular member in the axial direction of the turbine rotor.

8. The variable nozzle mechanism according to claim 1 ,

wherein, of the inner peripheral edge, a connection portion between a surface of the first annular member facing the second annular member and an inner peripheral surface of the first annular member has a rounded shape in an angular range in which the recess portion does not exist in the circumferential direction of the turbine rotor.

9. The variable nozzle mechanism according to claim 1 ,

wherein each of the plurality of second inner edge portions has a recess portion formed thereon, the recess portion being recessed outward in the radial direction of the turbine rotor.

10. The variable nozzle mechanism according to claim 1 ,

wherein the inner peripheral edge has recess portions curved so as to be recessed outward in the radial direction of the turbine rotor and protruding portions connecting to the curved recess portions smoothly and curved so as to protrude inward in the radial direction of the turbine rotor, the recess portions and the protruding portions being formed alternately, and

wherein each of the second inner edge portions has one of the recess portions.

11. A variable geometry turbocharger, comprising:

the turbine rotor;

a turbine casing housing the turbine rotor and forming a scroll flow passage into which exhaust gas from an engine flows; and

the variable nozzle mechanism according to claim 1 ,

wherein exhaust gas passes through the scroll flow passage and then is supplied to the turbine rotor via the variable nozzle mechanism.

12. The variable nozzle mechanism according to claim 1 ,

wherein the recess portion is disposed next to the exhaust gas flow passage.

13. The variable nozzle mechanism according to claim 1 ,

wherein the first annular member is an annular plate disposed on the radially outer side of the turbine rotor.

14. A variable nozzle mechanism for a variable geometry turbocharger, comprising:

a first annular member;

a second annular member disposed so as to face the first annular member and forming an exhaust gas flow passage having an annular shape between the first annular member and the second annular member, for guiding exhaust gas to a turbine rotor of the turbo charger from a scroll flow passage formed on a radially outer side of the turbine rotor; and

a plurality of nozzle vanes supported rotatably on the first annular member and configured to be capable of adjusting a flow passage area of the exhaust gas flow passage,

wherein the first annular member has a plurality of support holes for supporting the plurality of nozzle vanes rotatably, the support holes being disposed at intervals in a circumferential direction of the turbine rotor,

wherein an inner peripheral edge of the first annular member includes a first inner peripheral edge having a first inner diameter that engages a casing of the variable geometry turbocharger and a second inner peripheral edge having a second inner diameter smaller than the first inner diameter, and the second inner peripheral edge includes a plurality of first inner edge portions belonging to an angular range in which the support holes exist in the circumferential direction of the turbine rotor and a plurality of second inner edge portions belonging to an angular range in which the support holes do not exist in the circumferential direction of the turbine rotor, and

wherein at least one second inner edge portion of the plurality of second inner edge portions comprises a recess portion recessed outward in a radial direction of the turbine rotor, the recess portion extending in an axial direction of the turbine rotor from the side of the exhaust gas flow passage.