After years of existing in the periphery of automotive performance tuning- and, quite literally, in the periphery of low-budget tuning magazines- electric superchargers are finally ready to hit the road for real under the hoods of Volkswagens, Audis, and Volvos.
A supercharger is a compressor that forces more air into the combustion chamber. The effect is like fanning the flames of a campfire to make it burn hotter. We get more ooomph from a supercharged engine when we press on the loud pedal. There is no free lunch, of course. It takes energy to spin a supercharger and connecting one to the engine through belts, or clutches can be an engineering nightmare. Exhaust driven turbochargers are more mechanically efficient, but they take time to build compression (or, “boost”). Most of us know this delay as “turbo lag”, the difference in time between when you mash the throttle and when the extra power kicks in.
Both Audi’s RS5 TDI and Volvo’s High Performance Drive-E use electric superchargers to supplement engines that are already turbocharged. The electric compressor can spin up from rest to 70,000 rpm in about a quarter of a second, providing instant boost on demand. Once engine revs rise, the electric supercharger shuts off and the turbo takes over. From the driver’s seat, the impression is of one long, continuous burst of power with no gaps. Using an electric supercharger also provides a significant boost to fuel economy because the engine can get more power out of a given amount of gasoline, as demonstrated by the HyBoost Ford Focus project.
Adding an electric supercharger is easy. All you need is a bracket to hang it from and an electric wire to the power source. And that’s where things get interesting. The true beauty of an electric supercharger is that it uses stored electricity harvested during normal driving. Because a regular battery is slow to charge and slow to release its energy, the key component is the supercapacitor – an energy storage device that charges and discharges almost instantaneously.
While it does not have the power density of a battery, it doesn’t need to, since the electric supercharger operates only for short intervals – usually 1 to 2 seconds -every once in a while. Supercapacitors cost more than a comparable battery at present, but prices are coming down rapidly, thanks in part to the use of graphene. Another key to using electric superchargers successfully is the software that controls the complex relationship between it and the turbocharger so the driver feels only a seamless flow of power.
Turbochargers are already standard equipment on many cars today. As manufacturers struggle to meet ever tightening fuel economy standards around the world, look for electric superchargers to find their way under the hood of more and more mainstream automobiles.
Source | Images: Road & Track, via Popular Mechanics.