Turbocharger having a meridionally divided turbine housing and a variable turbine nozzle
A turbocharger has a meridionally divided turbine housing defining a first scroll and a first nozzle, and a second scroll and a second nozzle. The first and second nozzles are divided from each other by a shroud plate mounted within the nozzle, for isolating the exhaust gas streams flowing through the two nozzles from each other. A plurality of circumferentially spaced vanes are rotatably mounted at a radially inner side of the nozzles. Leading-edge portions of the vanes are slotted to receive the shroud plate when the vanes are pivoted open. Trailing-edge portions of the vanes are unslotted. A radially inner periphery of the shroud plate includes cutouts for abutting the trailing-edge portions of the vanes in the closed position, and includes contour portions for influencing a flow separation ratio of the turbine.
1. A turbocharger having a meridionally divided variable-nozzle turbine, comprising:
a turbine comprising a turbine housing and a turbine wheel mounted in the turbine housing and connected to a rotatable shaft for rotation therewith, the turbine housing defining a meridionally divided scroll extending circumferentially and surrounding the turbine wheel, the meridionally divided scroll defining a first scroll extending substantially fully about the turbine wheel and a separate second scroll extending substantially fully about the turbine wheel;
the turbine housing defining a separate inlet for each of the first and second scrolls through which separate first and second exhaust gas streams are received;
a nozzle leading from the meridionally divided scroll generally radially inwardly to the turbine wheel;
a compressor comprising a compressor housing and a compressor wheel mounted in the compressor housing and connected to the rotatable shaft for rotation therewith;
a center housing connected between the compressor housing and the turbine housing and containing bearings for the shaft;
a generally annular nozzle ring having a first face that comprises one wall of the nozzle and that is axially spaced from an opposite wall of the nozzle;
a generally annular shroud plate mounted within the nozzle and having a radially outer periphery and a radially inner periphery, the shroud plate meridionally dividing the nozzle into a first nozzle and a second nozzle, the first nozzle receiving the first exhaust gas stream from the first scroll, the second nozzle receiving the second exhaust gas stream from the second scroll; and
a plurality of circumferentially spaced vanes disposed proximate a radially inner extremity of the first nozzle and the second nozzle, each of the plurality of vanes being joined to a vane shaft disposed at a location intermediate a leading edge and a trailing edge of each of the plurality of vanes, the vane shafts being rotatably mounted to the nozzle ring such that the plurality of vanes are pivotable between an open position and a closed position for regulating exhaust gas flow to the turbine wheel, each of the plurality of vanes defining a slot extending from the leading edge radially inwardly to the vane shaft, the slot receiving the shroud plate when the vanes are pivoted to the open position such that first leading-edge portions of the vanes on a first side of the shroud plate are within the first nozzle and second leading-edge portions of the vanes on a second side of the shroud plate are within the second nozzle, and wherein trailing-edge portions of the vanes radially inwardly of the vane shafts are free of slots.
2. The turbocharger of claim 1 , wherein the radially inner periphery of the shroud plate defines a plurality of circumferentially spaced cutouts, there being one of the plurality of cutouts for each of the plurality of vanes, and wherein the radially inner periphery further defines a plurality of contour portions interspersed respectively between the plurality of cutouts, there being one of the plurality of contour portions for each of the plurality of vanes, the plurality of cutouts lying at a radius greater than that of the plurality of contour portions, the plurality of cutouts being configured to be abutted by the trailing-edge portions of the plurality of vanes when the plurality of vanes are pivoted to the closed position.
3. The turbocharger of claim 2 , wherein a flow separation ratio of the nozzle is a function of a degree to which the plurality of contour portions extend radially inwardly farther than the plurality of cutouts.
4. The turbocharger of claim 1 , wherein the radially inner periphery of the shroud plate defines a plurality of circumferentially spaced vane-shaft-bearing recesses of semi-circular shape for respectively engaging the vane shafts.
5. The turbocharger of claim 1 , further comprising a plurality of first spacers disposed between the nozzle ring and the shroud plate to govern a first axial spacing between the first face of the nozzle ring and the shroud plate, and a plurality of second spacers disposed between the shroud plate and the opposite wall of the nozzle to govern a second axial spacing between the shroud plate and the opposite wall of the nozzle.
6. The turbocharger of claim 5 , wherein each of the plurality of first spacers includes a pin of smaller diameter than the first spacer, the pin having a first portion that projects axially from one side of the first spacer toward the nozzle ring, and wherein the nozzle ring defines a plurality of first receiving holes that respectively receive the first portions of the pins of the plurality of first spacers.
7. The turbocharger of claim 6 , wherein the pin of each of the plurality of first spacers also includes a second portion that projects axially from an opposite side of the first spacer toward the opposite wall of the nozzle, the second portions of the pins passing through pin-receiving holes in the shroud plate, and wherein the opposite wall of the nozzle defines a plurality of second receiving holes that respectively receive ends of the second portions of the pins of the plurality of first spacers.
8. The turbocharger of claim 7 , wherein the plurality of second spacers comprise sleeves of greater diameter than the pins of the plurality of first spacers, each sleeve defining a central bore through which a respective one of the pins of the plurality of first spacers passes.
9. The turbocharger of claim 7 , wherein the opposite wall of the nozzle is defined by an annular insert and the turbine housing defines an annular recess in which the annular insert is disposed, and wherein the annular insert defines the plurality of second receiving holes for the pins.
10. The turbocharger of claim 9 , wherein the plurality of second receiving holes pass entirely through an axial thickness of the annular insert and wherein the turbine housing defines a plurality of blind holes that align with the plurality of second receiving holes and that receive terminal ends of the second portions of the pins.