As an effective means of improving engine output, turbocharging has been widely used in engines. However, due to the inherent mismatch of a turbocharger to a reciprocating machine, a turbocharged machine does have some drawbacks,such as the reduction in transient performance, low torque backup, low torque and etc. One solution to these problems is to dynamically vary the size of the turbine stage, reducing the swallowing capacity of the turbine at lower gasflows and increasing the swallowing capacity at high gasflows. A turbocharger fitted with such a turbine is called “Variable Geometry” turbocharger.
In general, there are two types of variable nozzle turbocharger. One is the traditional gas turbine approach of using a set of individually pivotable nozzle guide vanes (