In hybrid and electric cars, regenerative braking systems are used to convert kinetic energy into electrical energy under braking, slowing the car down and improving gas mileage or all-electric range.

But Nissan’s latest iteration of the Japanese-market Serena minivan uses regenerative braking technology as a way to eke out extra gas mileage from a regular gasoline engine. 

Called the S-Hybrid -- standing for “simple and smart” -- the system features an upgraded version of the ECO stop-start motor found in current generation Serena minivans, which replaces the alternator found in conventional cars. 

Despite its name however, it is not a true hybrid system: the motor cannot provide any power to move the car along, only recapture it. Nor does it store energy in a large hybrid battery pack. 

Under braking, the engine stops and the ECO motor engages to generate electricity that recharges a pair of 12-Volt batteries. The generated power is then used as required by the car to run its 12-volt accessories and computer systems. 

When it needs to move off, the ECO motor acts as a starter motor, restarting the gasoline engine and letting the car move away.

In a traditional gasoline-powered car, the on-board electrical systems are powered by an engine-driven alternator. This puts a continuous, parasitic draw on the engine, reducing its efficiency.

Mazda i-ELOOP capacitor-based regenerative braking technology

Mazda i-ELOOP capacitor-based regenerative braking technology

Because it eliminates that continuous power drain, Nissan claims its S-Hybrid technology can improve fuel economy by around 10 percent, although it should be noted this figure has not been independently verified.

It is also substantially cheaper than a full hybrid drivetrain, since it does not require a high-voltage hybrid battery pack.

Nissan hasn’t said yet if the technology will ever make it to the U.S., but even if it doesn’t, lots of other automakers are tackling the problem of parasitic power draw in innovative ways. 

In some of its cars, BMW employs a regenerative alternator that is clutched only when the engine is on overrun, not when maximum power is required.  

Next year, the 2014 Mazda6 Sedan will introduce a system called i-Eloop. Similar to Nissan’s S-Hybrid, i-Eloop recaptures energy under regenerative braking to power on-board electrical systems. Instead of storing recaptured energy in a battery however, it uses a large capacitor to store energy until it is needed. 


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