While Toyota took out the Tokachi 24-Hour Race in 2007 with a Supra HV-R hybrid race car featuring a quick-charging supercapacitor-based regenerative braking system, battery storage has so far been the norm for these systems in production vehicles. Now Mazda is charging things up with its new "i-ELOOP" system intended for internal combustion engine-powered vehicles. The i-ELOOP is billed as the world's first passenger vehicle regenerative braking system that uses a capacitor in place of rechargeable batteries to temporarily store energy captured from braking.

Regenerative braking systems used in most current hybrid and electric vehicles convert a vehicle's kinetic energy as it decelerates into electricity, which is used to recharge a battery that powers an electric motor. In contrast, Mazda's new "i-ELOOP" (Intelligent Energy Loop) system is designed to be used in internal combustion engine-powered cars with the energy captured used to power the climate control, audio system and other electrical components. This gives the system the advantage of not requiring a dedicated electric motor or battery.

Mazda claims the i-ELOOP system improves the fuel economy of a vehicle by around 10 percent under real-world driving conditions with frequent acceleration and braking.

i-ELOOP uses a new 12-25 V variable voltage alternator that generates electricity at up to 25 V before sending it to a low-resistance Electric Double Layer Capacitor (EDLC) for storage. Because capacitors can be charged and discharged much more quickly than batteries, the capacitor used in the i-ELOOP system can be fully charged in seconds. A DC/DC converter then steps down the electricity from 25 V to 12 V before distributing it directly to the vehicle's electrical components.

The system is also used to charge the vehicle's battery when necessary and works in conjunction with Mazda's i-stop idling technology to extend the period that the engine can be shut off.

The new i-ELOOP system, along with its range of SKYACTIV technologies, fits in with Mazda's focus on improving the efficiency of internal combustion engine vehicles rather than developing hybrid electric vehicle technology of its own, having opted instead to license technology used in the Toyota Prius for any near-future hybrid vehicles. Mazda says the i-ELOOP system will start to appear in its vehicles in 2012.