Electrically assisted turbochargers: Their potential for energy recovery

This paper describes the integration of a high-speed 7.5 kW electric motor-generator within a standard turbocharger of a heavy-duty vehicle and examines the impact it can have on vehicle performance. The electrical machine is used to help accelerate the turbocharger up to operating speed so reducing emissions and smoke production. The electric machine is also operated as a generator at high engine loads, when excess power is available in the exhaust. By returning energy to the vehicle electrical system the mechanical load placed on the drive shaft by the electrical alternators can be reduced leading to improvements in fuel efficiency. Using such a motor-generator smoke production is substantially reduced whilst the fuel economy of a 12 tonne city bus can be increased by up to 6% depending on operating conditions