Nowadays, the electric supercharger for turbocharged downsized automotive engines is mainly used to improve torque at low engine speeds in order to obtain an enhancement of the time to boost. These components are usually designed to fill the gap in terms of torque in transient operation caused by the main turbocharger with reference to the typical turbo lag issues.
An advanced solution of the engine boosting system is taken into account, considering the adoption of an electrically assisted compressor (e-compressor) coupled to a waste-gated turbocharger, typically adopted alone, in order to provide a reduced turbo-lag.
In order to highlight the behavior of the electric supercharger coupled to the turbocharger, the first experimental investigation regarded the steady flow characterization of the compressor. Due to problems related to over temperature, the working time of the e-compressor is limited avoiding an accurate evaluation of compressor efficiency, which is related to the upstream and downstream temperature measurements. A driving system (instead of the electric machine) was designed by the authors to provide a more accurate evaluation of the compressor map. To this aim, a turbocharger turbine has been selected according to the requested power levels.
The experimental investigation was developed at the turbocharger test facility of the University of Genoa using different sensors for the measurements of the average levels of thermodynamic quantities. Besides, accelerometers and microphones were adopted to measure noise and vibrations operative levels in order to check the correct operative functionality of the system. Finally, the transient response of the e-compressor coupled to the main turbocharger is reported to highlight the benefit in terms of the engine time to boost.