Turbocharger

A turbocharger, comprising:

• a turbine rotor;
• a turbine housing which includes a turbine-housing side flange portion on a radially outer side, and which accommodates the turbine rotor;
• a bearing device rotatably supporting a shaft connected to the turbine rotor;
• and
• a bearing housing which includes, on a radially outer side, a bearing-housing side flange portion facing the turbine-housing side flange portion, and which accommodates the bearing device;
• and
• a clamp gripping the turbine-housing side flange portion and the bearing-housing side flange portion to couple the turbine housing and the bearing housing,
• wherein, in a state where the turbine housing and the bearing housing are coupled by the clamp, an elastic force in a direction to separate the turbine-housing side flange portion and the bearing-housing side flange portion from each other is applied to each of the turbine housing and the bearing housing,
• wherein the turbocharger further comprises a biasing member disposed between the turbine housing and the bearing housing, and configured to bias the turbine housing and the bearing housing so as to apply the elastic force to the turbine housing and the bearing housing,
• wherein the biasing member is a back plate disposed between the turbine rotor and the bearing housing,
• wherein at least a part of the back plate is held between the turbine housing and the bearing housing in an elastically deformed state,
• wherein the back plate is supported on the turbine housing from a first side in an axial direction of the turbine rotor and is supported on the bearing housing from a second side in the axial direction,
• wherein the back plate is configured to satisfy an expression df−di<δ0−δ1, where
• δ is a step in the axial direction between a back-plate side first supported portion of the back plate supported on the turbine housing, and a back-plate side second supported portion of the back plate supported on the bearing housing, δ0 is the step δ in a natural state of the back plate, δ1 is an initial step δ of the step δ in an initial state after the back plate is mounted,
• d is a distance in the axial direction between a turbine-housing side support portion of the turbine housing supporting the back-plate side first supported portion and a bearing-housing side support portion of the bearing housing supporting the back-plate side second supported portion, di is the distance d in the initial state, and df is the distance d at the time when the turbocharger is at full load,
• wherein the turbine housing supports a radially outer portion of the back plate in the axial direction of the turbine rotor from a side of the turbine rotor against the elastic force, wherein the bearing housing supports the radially outer portion of the back plate in the axial direction from a side opposite to the turbine rotor against the elastic force, and
• wherein an inner peripheral edge of the back plate is a free end separated from the bearing housing.