An electrically-controlled supercharger from a US partnership is claimed to deliver a reduction in CO2 emissions of over 18 per cent while retaining the performance and driving feel of a large conventional engine, even at low engine speeds.

The introduction of downsized and boosted engines is expected to provide a major contribution to the reduction of CO2 emissions in future generations of passenger vehicles, but the challenge of giving downsized engines the driveability characteristics demanded by consumers has so far delayed their adoption by volume car makers.

Automotive engineering specialist Integral Powertrain, together with partner DriveTec, has developed and patented a system, SuperGen, which involves a variable-speed, electrically-controlled supercharger design that takes most of its power from a physical link to the vehicle’s engine. Electrical energy from the vehicle generator is used to power an advanced gearing system that can accurately vary the speed of the turbo compressor from zero up to 150 times crank speed.

By removing the link between engine and compressor speed, SuperGen allows the use of centrifugal compressors, delivering much reduced parasitic losses and improved boosting efficiency compared to conventional supercharging systems. The key to the SuperGen concept lies in the combination of a patented epicyclic traction transmission and electric gear ratio control. Used to vary the speed of the compressor between zero and up to 150 times crankshaft speed, the SuperGen transmission allows the compressor to spin at up to 225,000rpm.

Speed control in the SuperGen system is provided by a small electric motor, which imparts extra motion to the planet hubs of the epicyclic transmission. The approach needs few special components and provides a mechanical link between the engine and the compressor.

SuperGen can deliver strong boost at all engine speeds with transient response being as quick as the vehicle driveline can normally handle. The compressor shaft can be accelerated from rest to 150,000rpm in less than 300 milliseconds. The device is suitable for boosting downsized engines of up to 200hp capacity.

Integral Powertrain is an independent consultancy, while DriveTec was established to develop power transmission technologies based on an Electric Power Split Drive (EPS), comprising two electric motor/generator units coupled to a basic gearing system, thus providing a transmission system with infinitely variable gearing ratios.