Patent ID: 8640459

Claim:
A method for operating a turbocharged internal combustion engine system comprising a high-pressure variable geometry turbocharger (VGT), a low-pressure turbocharger used to control air entering an engine, and an electronic circuit controller, the method comprising: determining a transition from a dual turbo mode to a single turbo mode, wherein the high-pressure variable geometry turbocharger is active in the dual turbo mode and idle in the single turbo mode; determining a desired turbine efficiency across the high-pressure variable geometry turbocharger based on the determination of the transition; controlling a turbine of the high-pressure variable geometry turbocharger to maintain the desired turbine efficiency during the transition from the dual turbo mode to the single turbo mode; controlling a bypass valve and a volume flow rate through the turbine determined by position of variable inlet guide vanes of the turbine of the high-pressure variable geometry turbocharger, wherein the desired turbine efficiency is a predetermined turbine efficiency based on the position of the variable inlet guide vanes and a pressure ratio, and wherein the pressure ratio is a ratio of exhaust gas flow rate pressure through a turbine inlet to a turbine outlet of the high-pressure variable geometry turbocharger; and opening the bypass valve when the pressure ratio exceeds a threshold pressure.