Developing a NEXT-GEN VGT

Engineers from Mitsubishi Heavy Industries refine the design of a variable geometry turbocharger for commercial vehicles.

Variable geometry turbochargers (VGT) have been applied to commercial engines for a long time, owing to their operability at wide operation range. One of the major advantages of using a VGT is its ability to provide high boost pressure at low engine speeds, which ensures optimum supply of air for proper combustion, leading to a significant reduction in emissions. Recent emission standards by U.S. EPA and in Europe (Euro VI) demand a higher efficiency from the turbine at all operating points, which motivated engineers from Mitsubishi Heavy Industries to do an in-depth loss analysis of each component and carry out design modifications to achieve these demands.

The multi-vane VGT, which has been found to be the most effective among all the configurations, consists of a plurality of nozzle vanes distributed circumferentially upstream of the radial turbine rotor. These vanes are controlled by an electric actuator working in coherence with the engine control unit (ECU) to control the mass flow rate entering the rotor. There are many different types of link mechanisms to transfer the actuation force to the vanes; the authors selected a mechanism consisting of a plurality of lever arms connected to each vane, driven by a drive ring moved circumferentially using a crank arm connected to the actuator.