The 12 university FutureCar teams took radically different approaches.
Eleven cars were hybrids, with electric motors coupled to some kind of traditional engine. Four were "series hybrids," electric cars that used the engine to recharge the batteries. The rest were "parallel hybrids," using engines and electric motors simultaneously. Four ran on diesel fuel; four on gasoline; two on compressed natural gas; one on ethanol; and one on propane.
Only one of the hybrid electric cars required plugging in. The other 10 used their on-board engines to recharge the batteries (though most had external wall plugs as well).
The eight parallel-hybrid cars used a variety of approaches, including:
* Electric assist - where the electrical system supplements a small, low-power engine on hills or under acceleration, then recharges the batteries when it has extra power.
* Torque equalizing - a system that constantly adjusts the amount of power coming from the engine and electric motor, depending on which is more efficient and cleaner.
* Part-time hybrid - a system that shuts off the engine at low speeds, starts it in second gear, uses hardly any electricity on the freeway, and turns the engine off down hills. This "charge-depleting" car has to plugged in to recharge its batteries at the end of the day.
The advantage of all these approaches is that they allow the cars to use a smaller, cleaner, harder-working internal combustion engine than today's cars have, without sacrificing acceleration. They also sport much smaller, lighter battery packs than electric cars and have greater range.