Abstract
Stricter fuel consumption and emission regulations have put worldwide car makers and suppliers under pressure to develop more efficient vehicle systems. Engine downsizing by supercharging has gained significant interest due to benefits of lower fuel costs and reduced emission pollutants with marked performance gains. The supercharging systems, utilizing both positive displacement and turbo compressors, typically suffer from „linear charging‟, inefficiency, and lack of durability. Both technologies are driven by belt, sometimes geared, and offer engine charging whether required or not.
To overcome linear charging, electrically driven machines have been devised that use conventional (back-swept) turbo machine designs at ultra-high speed via a high ratio step-down gear box or a very high speed electric motor. These suffer from parasitic losses, inefficiency and high cost due to costly bearings, gearbox and motor/driver. Turbochargers that utilize exhaust energy are therefore preferred to superchargers despite turbo-lag. An electrically driven supercharger (EDS) using TurboClawTM technology crucially operates at low speed enabling direct motor drive. This provides the additional benefit of offering engine charging only when it is actually required.
In the reported work, an electrically-driven supercharger supporting downsizing of engines with a displacement of 1.4 L is developed. The system comprises an innovative low specific speed turbo-compressor driven by a brushless DC motor. The system performance has been simulated for fuel economy reduction on a supercharged 1.0 L gasoline engine in a B-segment vehicle as compared to a 1.4 L naturally aspirated engine whilst maintaining the vehicle performance. A control strategy for the system has been developed and integrated into the system. A prototype and a specially designed test rig have been built and the control functionality has been tested on Hardware in the Loop (HiL) rig. The results from the simulation and the testing show significant improvement in fuel economy on the NEDC cycle while delivering high speed acceleration target vehicle performance. Other variants such as combining the system with a turbocharger have also been investigated.
KEYWORDS: Supercharger, Downsizing, Fuel economy, Engine, Simulation