All-electric trucks are exciting, but the reality is that in the heavy-duty world, range-extended hybrids are a more practical stepping stone into electrification. Hyliion recently introduced the 6X4HE, a electric drivetrain system for Class 8 diesel trucks.

The Hyliion 6X4HE can be installed on new or retrofitted onto existing Class 8 trucks, and works without any driver interaction. According to the company, regenerative braking captures power when slowing down, then electric power is applied when necessary to keep diesel engines at their most efficient RPM, delivering hybrid fuel savings. Additionally, the APU uses Hyliion’s proprietary cooling system and battery to deliver 18,000 BTUs for 10 hours on a single charge.

Hyliion Chief Executive Officer Thomas Healy describes the system as bringing the “Toyota Prius concept” to heavy-duty vehicles.

“What we do is we take your conventional, diesel-powered truck and add on an electric axle and battery pack system,” Healy explains. “When the vehicle is slowing down or going downhill, we can capture all that wasted energy and store it in the battery pack for when the vehicle accelerates or goes uphill. Then we can take that energy and use it to help propel the vehicle forward. By doing that, the diesel engine doesn’t have to work as hard.”

The system can also be used as an APU, which adds to the fuel economy savings.

Ryder, PAM Transport and Mesilla Valley Transport assisted with the development of the system, with all three receiving first-delivery “beta” units, and reporting their feedback to Hyliion, who then made adjustments to what became the final product.

“On the technology side, the whole goal is to keep the diesel engine in its sweet spot. What we’re doing is looking at how hard the diesel engine is working—Is it downshifting? Is the engine revving up? Is it coasting and not consuming any fuel? Then our algorithms decide when to apply electric power or when to capture energy,” Healy explains.

“An example of this is if you’re climbing a hill, normally, the diesel engine would downshift and the RPMs would start climbing. You’d start consuming more fuel in order to maintain speed while climbing the hill. With our system, the goal is to not have the vehicle downshift so it stays in that higher gear, which causes the RPMs to stay lower and it to consume less fuel.”

The Hyliion system is designed for over-the-road, long-haul Class 8 applications specifically. Healy points out that the greatest fuel savings will be seen by trucks that frequently traverse hilly terrain and by drivers who sleep in their trucks and can realize the benefits of the APU. While Hyliion’s hybrid systems are only available in Class 8 applications at the moment, Healy says they are working on bringing it to medium-duty trucks as well.

“We have some customers already lined up in that category, actually, so it’s something that we’re working on with them,” he says.

Of course, the big reason to electrify a truck’s components is the potential to reduce the cost of ownership delivered through fuel savings. So let’s get right to the numbers.

According to the company, the Hyliion 6X4HE delivers a total of 30% fuel and emissions savings. This is broken down into three categories: 15% fuel savings from the electric hybrid drive axle, 12% from the APU, and 3% from aerodynamics. Healy says a hybrid system—like the electric drive Hyliion system on a diesel truck—is the most realistic option for an on-highway fleet with an eye on electric power.

“The fully electric trucks are a wonderful, ideal solution for short-haul, local delivery, where you can set up a recharging station at your warehouse and you can charge it up when it goes out for the day and when it gets back at night you can plug it back in,” Healy says. The way Healy sees it, building a sufficient network of charging station across the U.S. to recharge vehicles like a Class 8 electric truck is going to take more than a decade.

“A hybrid system has many of the benefits of a fully electric truck, but you can bring it in to your fleet now,” he continues. “You don’t need to recharge our system. You don’t need to plug it in. You just put it on the truck and it’s a self-sustaining system. You’re not going to see 100% fuel savings like you would with electric, but you’re going to see that stepping stone of 30% savings by using hybrid technology, and you don’t have any of the infrastructure problems or those big up-front costs.

“Electrification is the popular buzzword right now, and there’s a big push for it, but we feel that hybrid technology is what makes sense.”