Drivecycle Benefits of Controlling Airflow with the SuperTurbo™ 2018-01-0970
The SuperTurbo™ is a driven turbocharger that uses a high-speed traction drive combined with a CVT (Continuously Variable Transmission) or electric motor to provide additional power to or from the turbo shaft. The CVT can be shifted to a ratio that provides a turbo speed that generates a desired boost pressure and air flow rate to the engine. Unlike a conventional turbocharger, where the turbine and compressor powers must be balanced, the a driven turbocharger can provide additional power to the turbo shaft through supercharging when the turbine is not collecting sufficient power to drive the compressor to the desired boost pressure, and during other operating conditions can absorb excess turbine power through turbo-compounding to improve engine efficiency. This direct control of air flow to the engine enables greater flexibility in engine operation. The topics presented focus on heavy-duty diesel engines, but the concepts can be applied to all engine types. Transient response is improved, as well as fuel efficiency during transient operation of diesel engines, as excess fueling to provide exhaust energy to the turbine is avoided. Instead, additional airflow is provided to the engine through supercharging to increase combustion efficiency. This aids in engine downspeeding, as well as downsizing, to provide improved drivability of the vehicle. Simulations and engine testing show that efficient transients can provide a fuel savings of up to 6% over a transient drivecycle, and the ability to downspeed the engine can provide an additional 3% efficiency gain. Overall, the ability to directly control airflow to the engine provides flexibility for engine operation that is not possible with a conventional turbocharger.