A turbocharger includes a compressor housing, a bearing housing and a back plate. A discharge scroll chamber has such a shape that a cross-sectional area thereof gradually increases toward a discharge port in a circumferential direction. The compressor housing includes a scroll piece assembled to a
A turbocharger includes a compressor housing, a bearing housing and a back plate. A discharge scroll chamber has such a shape that a cross-sectional area thereof gradually increases toward a discharge port in a circumferential direction. The compressor housing includes a scroll piece assembled to a shroud piece. The scroll piece includes a suction port-forming portion, a suction-side concave surface and a scroll outer periphery. The shroud piece includes a shroud fit-in portion, an inner peripheral concave surface, a shroud surface and a diffuser surface. The back plate includes a facing surface, an outer peripheral annular fit-in portion and an outer peripheral concave surface. The outer peripheral concave surface has such a shape that a cross sectional shape thereof formed by a plane including a rotation axis of an impeller gradually changes in the circumferential direction.
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1. A turbocharger comprising: a compressor housing provided therein with an air flow passage in which an impeller is disposed;a bearing housing rotatably supporting a rotor shaft which is connected to the impeller; anda back plate which is disposed between the bearing housing and the compressor hous
1. A turbocharger comprising: a compressor housing provided therein with an air flow passage in which an impeller is disposed;a bearing housing rotatably supporting a rotor shaft which is connected to the impeller; anda back plate which is disposed between the bearing housing and the compressor housing and which faces a part of the air flow passage, whereinthe air flow passage includes a suction port from which air is sucked toward the impeller, and a discharge scroll chamber which is formed on an outer peripheral side of the impeller in a circumferential direction, and which guides compressed air discharged from the impeller to a discharge port, the discharge scroll chamber has such a shape that a cross sectional area thereof gradually increases toward the discharge port in the circumferential direction,the compressor housing includes a scroll piece and a shroud piece which are mutually assembled,the scroll piece includes a cylindrical suction port-forming portion forming the suction port, a suction-side concave surface configuring a suction-side wall surface of the discharge scroll chamber, and a scroll outer periphery disposed on an outer peripheral side of the discharge scroll chamber,the shroud piece includes a cylindrical shroud fit-in portion which is fitted into the scroll piece, an inner peripheral concave surface configuring an inner peripheral wall surface of the discharge scroll chamber, a shroud surface facing to the impeller, and a diffuser surface extending from the shroud surface toward the discharge scroll chamber,the back plate includes a facing surface which is facing to the diffuser surface, an outer peripheral annular fit-in portion which is fitted into the scroll outer periphery of the scroll piece, and an outer peripheral concave surface configuring an outer peripheral wall surface of the discharge scroll chamber, andthe outer peripheral concave surface has such a shape that a cross sectional shape thereof formed by a plane including a rotation axis of the impeller gradually changes along the circumferential direction,wherein the back plate is fastened to the bearing housing through a bolt, a shaft hole through which the rotor shaft is inserted, a bolt hole through which the bolt is inserted and an oil discharge port through which lubricant is discharged are formed in a plate central portion of the back plate on an inner peripheral side thereof as compared with the facing surface, andwherein the oil discharge port is dented in a thickness direction of the back plate from a side of the bearing housing. 2. The turbocharger according to claim 1, wherein the cross sectional shape of the outer peripheral concave surface is formed such that a radius of curvature thereof gradually increases toward the discharge port in the circumferential direction. 3. The turbocharger according to claim 1, wherein the outer peripheral concave surface is formed such that a size thereof in an axial direction of the turbocharger gradually increases from its one end toward the other end in the circumferential direction. 4. The turbocharger according to claim 1, wherein the outer peripheral concave surface is formed such that a size thereof in a radial direction gradually increases toward the discharge port in the circumferential direction. 5. A method of producing the turbocharger according to claim 1, in which the scroll piece, the shroud piece and the back plate are individually casted, the scroll piece and the shroud piece are assembled to each other to obtain the compressor housing, the back plate is fastened to the bearing housing, and the compressor housing is assembled to the back plate to produce the turbocharger, wherein a mold to cast the back plate includes a body mold to form the facing surface, the outer peripheral annular fit-in portion and the outer peripheral concave surface, and a central mold to form the plate central portion, the central mold is detachably attached to the body mold, and the central mold is attached to the body mold such that a circumferential phase of the central mold is changed with respect to the body mold. 6. The turbocharger according to claim 1, wherein the oil discharge port is disposed between a pair of the bolt holes in the circumferential direction.
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