Lightning Hybrids, which builds aftermarket hybrid powertrains for fleet vehicles, uses a different type of power source for its regenerative braking system.

Unlike electrified hybrid systems, which rely on rechargeable batteries to store power from regenerative braking, Lightning Hybrids has developed what it calls a mechanical battery. The heart of this system is its two tanks – called accumulators – which move fluid from one to the next in a cyclical fashion as it stores and uses energy.

hybrid powertrains

A comparison of electric and hybrid regeneration, based on analysis from the University of Michigan Automotive Research Center. Source: Lightning Hybrids.

“Regenerative braking is all about capturing kinetic energy, storing it and releasing it,” says Ian Patterson, lead hydraulics engineer for Lightning Hybrids.

“Inside [one tank] is a nitrogen-filled rubber bag, called a bladder, which is compressed when hydraulic fluid gets pumped into the accumulator,” explained the company. “It takes energy to compress the bladder – just like it takes energy to compress a spring. A fully compressed bladder represents a lot of stored energy which on a hydraulic hybrid system can be released to propel the vehicle – hence the analogy of a ‘mechanical battery’ for the hydraulic accumulator.”

The video above illustrates how this hydraulic hybrid system powers a vehicle.

Lightning Hybrids systems can be installed on medium- and heavy-duty fleet vehicles as an aftermarket component. It’s compatible on vans such as the Freightliner, Mercedes-Benz Sprinter and Chevrolet Express, among other fleet models.

And installation is fairly straightforward. After removing the original brake pedal and driveshaft, technicians install a proprietary brake pedal, and the hydraulic hybrid powertrain takes the place of the driveshaft.

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Regenerative braking that incorporates a hydraulic system “has the advantage of high power density and the ability to accept the high rates/high frequencies of charging and discharging,” explained ER. Amitesh Kumar in the International Journal of Scientific and Engineering Research. This makes “hydraulic regenerative braking technology well suited for off-road vehicles and heavy-duty trucks.”

The system uses up to 30 percent less fuel, according to Lighting Hybrids, and emits 90 percent fewer emissions. And acceleration gets a boost from the swap, said the company. More information on the system can be found at the company’s website.