Variable geometry turbocharger

1. A variable geometry turbocharger, comprising:

a turbine rotor;

a turbine housing which accommodates the turbine rotor and which forms a scroll flow passage on a radially outer side of the turbine rotor;

a bearing housing accommodating a bearing which rotatably supports the turbine rotor, the bearing housing being coupled to the turbine housing; and

a variable nozzle mechanism for adjusting a flow of exhaust gas to the turbine rotor from the scroll flow passage,

wherein the variable nozzle mechanism includes:

a nozzle vane disposed in an exhaust gas flow passage for guiding the exhaust gas from the scroll flow passage to the turbine rotor;

a nozzle mount having an annular shape and supporting the nozzle vane rotatably, the nozzle mount forming a flow passage wall on a bearing-housing side of the exhaust gas flow passage; and

a nozzle plate having an annular shape and being disposed so as to face the nozzle mount, the nozzle plate forming a flow passage wall, of the exhaust gas flow passage,

a plurality of bolts disposed at intervals in a circumferential direction of the turbine rotor and configured to fasten the turbine housing and the bearing housing in the axial direction,

wherein the bearing housing includes a bearing-housing side support portion configured to support a radially outer portion of the nozzle mount from a side opposite to the scroll flow passage in an axial direction of the turbine rotor,

wherein the bearing-housing side support portion includes at least one bearing-housing side recess portion formed so as to be recessed toward a side opposite to the nozzle mount in the axial direction,

wherein the at least one bearing-housing side recess portion includes a plurality of bearing-housing side recess portions disposed at intervals in a circumferential direction of the turbine rotor, and

wherein the bearing-housing side recess portion is formed in an angular range which does not overlap with a center position of a bolt adjacent to the bearing-housing side recess portion, of the plurality of bolts, in the circumferential direction.

2. The variable geometry turbocharger according to claim 1 ,

wherein the bearing-housing side recess portion is formed to be 5 degrees or more apart from the center position of the bolt adjacent to the bearing-housing side recess portion, of the plurality of bolts, in the circumferential direction.

3. The variable geometry turbocharger according to claim 1 ,

wherein the turbine housing includes a turbine-housing side support portion configured to support the radially outer portion of the nozzle mount from a side opposite to the bearing-housing side support portion in the axial direction,

wherein the nozzle mount is nipped by the turbine-housing side support portion and the bearing-housing side support portion, and

wherein the turbine-housing side support portion is disposed so as to protrude toward an inner side of the bearing-housing side support portion in a radial direction of the turbine rotor, along a surface of the nozzle mount.

4. The variable geometry turbocharger according to claim 3 ,

wherein the turbine-housing side support portion includes a contact portion to be in contact with the radially outer portion of the nozzle mount, and a non-contact portion formed on an inner side of the contact portion in the radial direction, the non-contact portion facing the nozzle mount via a gap.

5. The variable geometry turbocharger according to claim 3 ,

wherein an expression 0≤(r1-r3)/(r2-r3)≤0.75 is satisfied, where r1 is a distance between a radially inner end of the turbine-housing side support portion and a rotational axis of the turbine rotor, r2 is a distance between a radially outer end of the nozzle mount and the rotational axis, and r3 is a distance between a radially outer end of the nozzle plate and the rotational axis.

6. The variable geometry turbocharger according to claim 5 ,

wherein an expression 0≤(r1-r3)/(r2-r3)≤0.30 is satisfied.

7. The variable geometry turbocharger according to claim 1 , further comprising:

a heat shield member disposed between the bearing-housing side support portion and the nozzle mount.

8. The variable geometry turbocharger according to claim 7 ,

wherein the heat shield member has a lower thermal conductivity than each of a thermal conductivity of the bearing housing and a thermal conductivity of the nozzle mount.

9. The variable geometry turbocharger according to claim 7 ,

wherein the heat shield member is formed of austenitic stainless steel or nickel-based alloy.

10. The variable geometry turbocharger according to claim 7 ,

wherein the heat shield member comprises a ring-shaped heat-shield plate disposed so that the bearing-housing side support portion and the nozzle mount do not make contact with each other over an entire angular range in a circumferential direction of the turbine rotor.

11. The variable geometry turbocharger according to claim 7 ,

wherein the heat shield member comprises a coating applied to the radially outer portion of the bearing-housing side support portion or the nozzle mount.