Electrifying Trucks: Add-on Turns Diesel Semis into Hybrids

Converting a diesel semi-truck into a hybrid electric vehicle could be as simple as adding a detachable unit behind the cab. The unit, or dolly, contains an electric motor, a battery pack, and a drive axle and could reduce diesel consumption by as much as 85%, according to the San Francisco-based manufacturer, Revoy.

Revoy’s dolly sits between the cab and the trailer to provide an electric boost. Image used courtesy of Revoy

The Electric Dolly

The Revoy dolly is four meters long and weighs 10 tonnes (10,000 kg). It attaches between the truck’s fifth wheel plate and the trailer, providing battery-electric power without requiring any permanent engine or drivetrain changes.

The battery pack uses lithium iron phosphate batteries and has a 575 kWh capacity, optimally providing 320-400 km (200 to 250 miles) of electric-only power. Like nearly all hybrid vehicles, it uses regenerative braking to charge the battery during braking.

In a pilot program with Ryder System, Inc., the dolly traveled 50,000 miles over a year and achieved an 80% to 95% reduction in diesel fuel use. It also cut emissions by about 85%.

The Revoy dolly. Image used courtesy of Revoy

The dolly can handle a fully loaded semi weighing up to 36 tonnes (80,000 pounds). It includes built-in safety features to prevent jackknifing, rollovers, and other operating risks.

Because the unit operates externally, it can easily be swapped out. When the battery is depleted, a fresh unit can be swapped in within a few minutes, eliminating long recharge times. Revoy’s long-range vision is to establish a network of swapping depots along major roads.

Expansion Plans

Revoy recently raised $27 million in Series A funding, bringing the company’s total to $41 million. Key investors included Standard Capital, Doerr Capital, Time Ventures, Y Combinator, and Leap Ventures.

Revoy plans to use the funding to expand operations and build a second-generation electric dolly with a smaller battery pack. The lower-cost unit is expected to maintain the same 200-mile range as its predecessor.

Watch how Revoy’s unit-swapping system could work. Video used courtesy of Revoy

The company plans to begin commercial operations along a 320 km (200-mile) corridor near Portland, Oregon. Two swap stations, with a fleet of four dollies, will be placed at either end to service 16 loads (or 8 round trips) daily.

First-of-its Kind Solution

Although other companies have developed devices to convert diesel fuel trucks into hybrids, Revoy has created the first completely external, detachable, and swappable unit. Other solutions require altering the drivetrain or other truck parts.

For example, in Europe, Trailer Dynamics builds semi-trailers equipped with battery packs up to 600 kWh and smart electric axles. It uses sensors on the trailer’s kingpin to detect pulling and braking forces, recovers energy through regenerative braking, and assists during acceleration. In tests on BMW trucks, the device saved up to 48% of fuel on long-distance hauls.

California-based Range Energy builds its device into the trailer. The battery pack and control system are mounted under the floor of a standard 53-foot box trailer. They replace the standard trailer axle with an electric axle with an integrated electric motor. The trailer’s kingpin also has sensors to detect load.

Revoy’s vision of swappable units, however, gives truck owners an option that eliminates up-front costs to retrofit or buy new trailers. The swapping program will be a pay-per-mile subscription.