Structure of scroll of variable-throat exhaust turbocharger and method for manufacturing the turbocharger

A scroll structure of a variable-throat turbocharger comprising:

• a scroll chamber in a turbine casing having an annular flow passage at an inner side of said scroll chamber for passing exhaust gas introduced to said scroll chamber to a radial flow turbine by passing through said annular flow passage, said turbine casing forming a circular wall that forms an inside wall of said scroll chamber, a supporting portion being provided at a stepped part of said turbine casing at an end of said circular wall;
• a plurality of nozzle vanes arranged in said annular flow passage having a variable blade angle;
• a nozzle throat area varying mechanism for varying the blade angle of said plurality of nozzle vanes, said nozzle throat area varying mechanism comprising a nozzle assembly unit which has:
• an annular nozzle mount and an annular nozzle plate rotatably supporting said plurality of nozzle vanes, and
• a plurality of nozzle supports connecting said nozzle mount to said nozzle plate so that said plurality of nozzle vanes are sandwiched between said nozzle mount and said nozzle plate;
• wherein said nozzle assembly unit is detachably attached to said turbine casing;
• wherein said nozzle plate of said nozzle assembly unit is located in said scroll chamber such that said nozzle plate forms an inside sidewall face of said scroll chamber and a wall face of said annular flow passage;
• wherein an inner periphery of said nozzle plate is fit on an outer periphery of said supporting portion provided at said end of said circular wall;
• wherein a circular groove is formed by a side face of said nozzle plate, said outer periphery of said supporting portion and a shoulder face of said stepped part of said turbine casing;
• and
• wherein a seal member is provided in said circular groove such that said scroll chamber is sealed against gas leakage from said scroll chamber to a point downstream of said annular flow passage.