Compressed-air-assisted turbocharger system for internal combustion engine

A turbocharger system for an internal combustion engine that powers a vehicle having a pressure vessel storing pressurized air. The turbocharger system comprises a turbocharger and a valve system. The system is configured such that the air intake system of the internal combustion engine can be supplied with air at super-atmospheric pressure either from the compressor of the turbocharger or from the pressure vessel. When the pressure vessel is supplying the intake system, compressed air from the compressor is recirculated back to the air inlet of the compressor so as to help prevent a surge condition in the compressor.