Turbocharger

1. A turbocharger comprising:

a bearing housing that rotationally supports an impeller shaft;

a turbine housing that is a cast component coupled to an end of the bearing housing in a rotation axis direction of the impeller shaft, wherein exhaust gas discharged from an internal combustion engine flows inside the turbine housing;

a turbine chamber defined in the turbine housing;

a turbine impeller that is accommodated in the turbine chamber and is configured to be rotated integrally with the impeller shaft by exhaust gas drawn into the turbine chamber;

a turbine scroll passage that is defined in the turbine housing and is a part of a passage for conducting exhaust gas that has flowed into the turbine housing to the turbine chamber, the turbine scroll passage surrounding a circumference of the turbine chamber;

a connecting passage that is defined in the turbine housing and connects the turbine scroll passage and the turbine chamber to each other;

an annular metal plate that constitutes a part of a wall surface of the connecting passage; and

a scroll passage defining plate that includes

a passage defining portion that is arranged such that a predetermined clearance is provided between the passage defining portion and the turbine housing, the passage defining portion constituting a part of a wall surface of the turbine scroll passage, and

an inner circumferential edge that extends from an inner circumferential edge portion of the passage defining portion and along the metal plate,

wherein the scroll passage defining plate is arranged in the turbine housing such that

the inner circumferential edge is fixed between the turbine housing and the metal plate, and

an outer circumferential edge portion of the passage defining portion that is on a side opposite from the inner circumferential edge portion is movable relative to the turbine housing.

2. The turbocharger according to claim 1 , wherein the scroll passage defining plate is arranged in the turbine housing such that the outer circumferential edge portion of the passage defining portion and an inner circumferential surface of the turbine housing are spaced apart from each other.

3. The turbocharger according to claim 1 , further comprising an elastic member configured to provide a clearance between the passage defining portion of the scroll passage defining plate and the turbine housing.

4. The turbocharger according to claim 3 , wherein

the elastic member is arranged between the outer circumferential edge portion of the passage defining portion and the turbine housing, and

the outer circumferential edge portion of the passage defining portion is supported by the turbine housing with the elastic member in between.

5. The turbocharger according to claim 1 , further comprising an annular leaf spring that is arranged between the inner circumferential edge of the scroll passage defining plate and the turbine housing,

wherein the scroll passage defining plate is fixed by holding the inner circumferential edge between the leaf spring and the metal plate.

6. The turbocharger according to claim 1 , wherein the scroll passage defining plate is fixed by holding the inner circumferential edge between the turbine housing and the metal plate.

7. The turbocharger according to claim 1 , wherein

the scroll passage defining plate includes

an outer circumferential wall that constitutes an outer circumferential interior surface of the turbine scroll passage,

an inner circumferential wall that is located inward from the outer circumferential wall in a radial direction of the impeller shaft and constitute an inner circumferential interior surface of the turbine scroll passage, and

a linking wall that links the outer circumferential wall and the inner circumferential wall to each other,

wherein the inner circumferential edge of the scroll passage defining plate extends from the inner circumferential wall and inward in the radial direction of the impeller shaft.

8. The turbocharger according to claim 1 , wherein a heat insulator is arranged in the clearance between the passage defining portion of the scroll passage defining plate and the turbine housing.

9. The turbocharger according to claim 1 , further comprising a plurality of nozzle vanes that is arranged in the connecting passage and causes exhaust gas in the turbine scroll passage to flow to the turbine chamber,

wherein the metal plate supports the nozzle vanes.

10. The turbocharger according to claim 9 , wherein

the nozzle vanes are movable vanes that are pivotally supported by the metal plate so as to be capable of changing a flow passage area of the connecting passage,

the turbocharger further comprises a metal support plate, and

the support plate cooperates with the metal plate to pivotally support the nozzle vanes and is arranged to be opposed to the metal plate so as to constitute a part of the wall surface of the connecting passage.

11. The turbocharger according to claim 10 , further comprising a metal annular plate, wherein

the annular plate is arranged to be opposed to the scroll passage defining plate so as to constitute a part of the wall surface of the turbine scroll passage,

a thickness of the annular plate is smaller than a thickness of the support plate, and a thickness of the metal plate, and

an outer circumferential edge of the annular plate is held between the turbine housing and the bearing housing.

12. The turbocharger according to claim 1 , further comprising a metal annular plate, wherein

the annular plate is arranged to be opposed to the scroll passage defining plate so as to constitute a part of the wall surface of the turbine scroll passage, and

an outer circumferential edge of the annular plate is held between the turbine housing and the bearing housing.

13. The turbocharger according to claim 12 , wherein

the annular plate includes a annular rib, and

the rib protrudes from an inner circumferential portion of the annular plate in the rotation axis direction of the impeller shaft and extends away from the scroll passage defining plate.

14. The turbocharger according to claim 12 , wherein

the scroll passage defining plate includes a flange portion that extends from the outer circumferential edge portion of the passage defining portion and outward in the radial direction of the impeller shaft,

a clearance is provided between the flange portion and the annular plate, and

the flange portion extends along the annular plate.

15. The turbocharger according to claim 14 , wherein the flange portion extends outward in the radial direction of the impeller shaft such that a clearance is provided between the flange portion of the scroll passage defining plate and the inner circumferential surface of the turbine housing.