Engineers for long have been challenged on what could be the best way of harvesting the ‘free’ engine power under braking. In 2009, Formula 1 racing cars started using KERS (Kinetic Energy Recovery System), a mechanism for recovering a moving vehicle's kinetic energy under braking. The energy thus recovered is stored either in a flywheel or in a battery for later use under acceleration.
In fact, brake energy regeneration has come to be regarded as the most common solution for such engineering challenges. The regenerated energy is used to recharge batteries in EVs and hybrids, for example, or to power the on-board electrical network and save engine power, and therefore, save fuel.
Japanese manufacturer Mazda, however, took a unique approach to brake energy regeneration by developing i-ELOOP (intelligent energy loop), claimed to be the world’s first passenger car system to use a capacitor in addition to a lead-acid battery to efficiently store and supply this electricity to the car’s electric components. The system also works in conjunction with Mazda’s idling stop system, i-stop, to realise an improvement of approximately 10 % in fuel economy.
Mazda used capacitors as they can deliver a large quantity of electricity over a short period of time and are extremely durable compared to traditional lead-acid batteries, which do not react well to repeated charging and discharging. The use of the capacitor will lead to significant increase in the life of the battery, also leading to a reduction in maintenance costs. The all-new Mazda6 is the first of Mazda’s SKYACTIV technology models to be available with i-ELOOP.
Mazda engineers utilised two breakthrough technologies to develop a system that efficiently recaptures kinetic energy, generates electricity, quickly stores it and allows that electricity to be used by the vehicle’s electrical components without waste. The first is the variable voltage alternator, capable of producing up to 25 V and 200 A, which is used to convert the car’s kinetic energy into electricity, and secondly, a low-resistance, high-capacity electric double layer capacitor (EDLC), which is used to store the electricity after regeneration.
A typical vehicle deceleration phase lasts only about 10 seconds. Realising that the effectiveness of regenerative braking systems to date has been limited by the charging and storage drawbacks of conventional lead-acid starter batteries, Mazda engineers adopted the EDLC, which recharges fully in only a few seconds. An efficient 12V-25V variable voltage alternator generates the electricity and charges the EDLC; a DC/DC converter then steps down the voltage to power electrical components such as the climate control air-conditioning and audio systems, with any surplus going to the starter battery.
Through the combined use of the capacitor and the variable voltage alternator, i-ELOOP is capable of regenerating about three times the energy of existing regeneration systems, which use only alternators and lead-acid batteries. It has also made it possible to supply almost all the electricity the vehicle needs, when driving through the regeneration system, freeing the engine from the work.
A fully-charged capacitor is enough to run the vehicle’s electrical systems for a minute or so. This makes i-ELOOP the perfect companion for i-stop – the latter launched as standard on the Mazda CX-5 and the all-new Mazda6 – as there is no need to revert to battery power even when Mazda’s idle-stop system has shut the car off. During stop-and-go city driving, charging often resumes before the capacitor is fully discharged. i-ELOOP can therefore produce most if not all of a vehicle’s electricity needs, whereas normally some of the engine’s output is required just to drive the alternator. By freeing up this engine capacity, i-ELOOP increases fuel economy under everyday driving conditions, the company claims.