Super fly: Derived from F1, flywheel systems will offer energy-efficiency benefits for road-ready hybrids. Stuart Nathan reports
A swift look around the streets will tell you that we’re in the age of the hybrid vehicle. The Toyota Prius was the vanguard, but most of the major automotive manufacturers have at least one hybrid model either on sale or about to reach the market.
These hybrids are battery electric, but that isn’t the only type of hybrid around. Hybrids, strictly speaking, are systems using more than one form of energy storage and release, and another, inspired by Formula 1, is likely to be making its marketplace debut in the next couple of years.
Flywheel hybrids are now under test by many of the automotive majors. They are a form of regenerative braking, versions of which have been available - mainly on high-end models - for some years. But while most regenerative braking systems use the energy to charge batteries or capacitors -thereby converting it from mechanical energy into chemical energy - flywheels simply shift it into another object. It is kinetic energy when it goes in, it’s stored as kinetic energy and it’s recovered as kinetic energy to make the car go faster.
’This is the key to why flywheels are an attractive prospect,’ explained Doug Cross, technical director of Flybrid, a small UK developer of automotive flywheel systems. ’We don’t have to convert the energy into another form.’ There are always efficiency losses when you convert the energy, he said; for an electrical-based regenerative system, the batteries won’t store as much energy as the car lost when it braked.
For this reason, F1 started taking a close interest in flywheels when the Federation Internationale de l’Automobile (FIA) opted to allow regenerative braking systems. The kinetic energy recovery systems (KERS) used in the 2009 racing season combined flywheel and battery, and with the motor-sport industry eager to see commercial returns for its developments, the shift from racing to road-ready systems is a top priority.
For Cross and his colleagues, KERS was a mixed blessing. ’We used to be employed in the Renault team’s engine-development division, but when the FIA froze engine development, we were basically out of a job. We stayed for six months developing the KERS, but after that we found ourselves in the pub with our redundancy cheques wondering what to do next.’
What was next was to start Flybrid to take the technology further, which took the team from the bosom of a big corporate enterprise to the world of the SME. ’We are not the classic 12 men in a shed,’ Cross insisted. ’There are 14 of us - and it’s a very nice, high-tech shed.’
Flybrid’s system is based around a lightweight flywheel that operates at very high rotational speeds. Its F1 pedigree is apparent in the concern for low weight, but there is a complex trade-off at work here, as the mass of the flywheel is integral to the amount of energy it can store. The lighter the wheel, the faster it needs to spin to store energy.