By Freddie Heaney:
If you reduce engine displacement by 50 percent, add an electrified turbocharger and connect it to an on-board battery pack what do you get? Amazingly…the same fast lap times while using 35 percent less fuel—and the elimination of turbo lag! We live in fascinating times.
For the 2014 racing season Formula One teams encountered their biggest challenge in decades. Generating toward 800hp, the former naturally aspirated 2.4 liter V8 racing engines, which had been revving to over 20,000rpm and more recently limited to 18,000rpm, were replaced by smaller, turbocharged 1.6 liter 90-degree V6 units accompanied by an on-board battery pack. The battery pack generates a further 160hp and uses an energy recovery system (ERS) to keep the battery charged. Assuredly, the changes have brought an abundance of new technologies in its wake.
What was the purpose? These efforts have been devised as an environmental gain by the sport’s ruling body, the FIA, to reduce fuel consumption to 100 kilograms (220lbs) per race. Races are limited to a maximum of 2 hours in duration. Under the new regulations refueling stops are no longer permitted. Miraculously, the new power units can complete a full race distance within seconds of last year’s times while using 35 percent less fuel thanks largely to the ERS.
The ERS recharges the battery pack by motor-generators connected to the electrified turbo and to the braking system. The function of the motor-generators is determined by the direction in which the electricity is flowing. If the electricity turns the shaft it functions as a motor. But if the engine spins the shaft it functions as a generator and recharges the battery.
How braking charges the battery pack
The braking system, known as brake-by-wire, works as follows: Under acceleration the electric motor-generator supplies extra power from the batteries to the drive wheels. Under braking the electrical flow is reversed and the kinetic energy of the driving wheels is redirected to charge the battery pack. As the electrical power needed to charge the batteries is generated by the rotating wheels via the crankshaft, the system acts as a brake, slowing down the drive wheels. This is known as regenerative braking and because it supplements the conventional braking system, traditional braking components have been reduced in size.
Controlled by complex software in the car, the function of regenerative braking is to balance the amount of electrical power harvested to charge the batteries with that expended on acceleration. Generating power usually costs power—a drive belt, for example, robs engine power to feed the electrical system—but this concept puts power losses to productive use: slowing the car and charging the battery.
Similarly the turbocharger
“The most important thing to understand about the electrical turbocharger,” says Borg Warner senior engineer, Mike Harris, “is that it is not just a turbo, but an integrated system comprising a turbine, an electric motor-generator and a compressor. Satisfying the very different needs of these components in a single, integrated package is quite the challenge.”
He went on, “Commercial vehicle manufacturers are attracted to this technology for the same reason F1 uses it: fuel economy. Everyone is looking for improved efficiencies. Currently, our interest lies with commercial diesel applications, especially ones with lots of stop-start cycles like buses or garbage trucks. Though turbochargers can operate at 100,000-plus rpm and transmit huge amounts of power, they lay at the heart of future automotive engine designs.”