Structure of scroll of variable-throat exhaust turbocharger and method for manufacturing the turbocharger
A ratio of cross sectional area A of a scroll passage to a scroll radius R (A/R) can be increased without increasing the size of a turbine casing and with very simple construction. An exhaust turbine capacity can thus be increased, so that a variable-throat exhaust turbocharger in which the engine output can be increased results. The turbocharger has a nozzle throat area varying mechanism of which a nozzle assembly unit is composed. A plurality of nozzle vanes are supported rotatably by an annular nozzle mount and an annular nozzle plate is connected to the nozzle mount by a plurality of nozzle supports to sandwich the nozzle vanes. The nozzle plate is located in the scroll chamber by attaching the nozzle assembly unit to the turbine casing to allow the nozzle plate to form part of the inside sidewall face of the scroll chamber and a wall face of the annular flow passage.
1. 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.
2. The scroll structure of a variable-throat turbocharger of claim 1 , wherein said nozzle plate has a plurality of through-holes that are arranged circumferentially in said nozzle plate and that receive said nozzle supports loosely fitted in said through-holes with a clearance between shaft end parts of said nozzle supports and an inner circumference of said through-holes.
3. The scroll structure of a variable-throat turbocharger of claim 1 , wherein said nozzle plate has a peripheral corner that is tapered or rounded toward an entrance of said annular flow passage so as to form a guide portion for smooth entrance of the exhaust gas in said scroll chamber to said annular flow passage.
4. The scroll structure of a variable-throat turbocharger of claim 1 , wherein said inside sidewall face of said nozzle plate comprises a rear face facing said scroll chamber that has a curved surface of revolution that continues smoothly to an inside circular surface of said circular wall.
5. The scroll structure of a variable-throat turbocharger of claim 1 , wherein said nozzle plate has a peripheral part that is bent such that said wall face of said annular flow passage has a curved surface that smoothly reduces said annular flow passage at an entrance thereof from said scroll chamber to form a guide portion smoothly introducing the exhaust gas from said scroll chamber into said annular flow passage.
6. A method of manufacturing a variable-throat exhaust turbocharger having 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 the scroll chamber to a radial flow turbine by passing through the annular flow passage, the turbine casing forming a circular wall that forms an inside wall of the scroll chamber, a supporting portion being provided at a stepped part of the turbine casing at an end of said circular wall, said method comprising:
manufacturing a nozzle assembly unit which has an annular nozzle mount and an annular nozzle plate rotatably supporting a plurality of nozzle vanes and a plurality of nozzle supports connecting the nozzle mount to the nozzle plate so that the plurality of nozzle vanes are sandwiched between the nozzle mount and the nozzle plate;
fitting a seal member to the supporting portion of the circular wall of the turbine casing in order that the scroll chamber can be sealed against gas leakage from the scroll chamber to a point downstream of the annular flow passage; and then
attaching the nozzle assembly unit to said turbine casing so that the nozzle plate forms an inside sidewall face of the scroll chamber and a wall face of the annular flow passage.