A few days ago we wrote about Bosch Engineering subsidiary Erphi Electronics’ new two-stage charging system for diesel engines that reduces “turbo lag”, and enables further engine downsizing. (Downsizing—i.e. using a smaller engine in a vehicle—being a great way to decrease fuel consumption and emissions.)
The Erphi charging system consists of two different-sized and connected turbo chargers. The smaller high-pressure charger kicks in at low engine speeds and is supplemented at medium speed by the larger low-pressure charger. When the control software switches the smaller charger off at higher speed, the larger charger completely takes over the air compression.
Now, the Engineer and Auto Industry UK report on an electrically-controlled, variable-speed supercharger being developed by Integral Powertrain in partnership with DriveTec, also designed to support downsizing.
A supercharger is similar in purpose to a turbocharger but differs in that the supercharger is powered by gearing, by belt- or by chain-drive from the engine’s crankshaft while the turbocharger is powered by exhaust gases driving a turbine.
Turbochargers are attractive in that they use otherwise wasted heat energy (the exhaust gases). The supercharger, on the other hand, uses power from the crank—but being mechanically-driven, it can react more quickly to start-up or low-speed acceleration.
Integral Powertrain/DriveTec’s Supergen supercharger uses an advanced gearing system that can accurately vary the speed of the compressor from zero up to 150 times crank speed—up to 225,000 rpm.
By removing the direct link between engine and compressor speed, SuperGen supports the use of centrifugal compressors (normally used in turbochargers), reducing parasitic power losses and improving boosting efficiency compared to conventional supercharging systems.
SuperGen delivers strong boost at all engine speeds with extremely quick response. The compressor shaft can be accelerated from rest to 150,000 rpm in less than 300 milliseconds.
SuperGen is based on the the combination of a patented epicyclic traction transmission and electric gear ratio control. A small electric motor, which imparts extra motion to the planet hubs of the epicyclic transmission, controls the compressor speed.
The device is suitable for boosting downsized engines of up to 200 hp capacity.
The Supergen is currently at the simulation phase. The developers are discussing a full prototype with a number of OEMs and are planning for the technology to enter series production in around three years.