A new type of variable nozzle turbine with a mixed-flow turbine rotor has been developed with the aim of satisfying a wide operating range and high efficiency of an automotive turbocharger. The dveloped variable nozzle is slanted in a radial direction to match the mixed flow turbine rotor and consists of alternate variable vanes and fixed vanes. The fixed vanes enable the clearance between the variable vanes and the housing wall to be minimized and prevent the variable vanes from sticking to the housing. It was shown that there was no sticking of the vanes due to thermal deformation on the condition that turbine was driven by combustion gas. It was shown that the existence of fixed vanes diminished the driven torque of the variable vanes based on the results of measurements of the axial force in the rod between the actuator and the variable vanes. In order to estimate the flow rates and the efficiencies of the developed turbines, aerodynamic performance tests were conducted. The improvements in turbine rotor shape and variable vane shape produced greter efficiencies. Consequently, the newly-developed variable nozzle turbine offers the characteristics of wide operating range and high efficiency.
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