DTNA’s SuperTruck II Separates the Practical from the Possible

Daimler Truck North America unveiled its SuperTruck II project in Las Vegas earlier this month. It doubles the freight efficiency of the baseline truck, a 2009 Freightliner Cascadia with a DD15 engine.

SuperTruck II builds on the learnings of SuperTruck 1, which wrapped up in 2015. DTNA’s SuperTruck 1 effort was a moon-shot of sorts, integrating some highly advanced technology. SuperTruck II was a little more grounded. It focused on more promising core components and systems with real-world applicability — technology that could be more easily integrated in near-future generations of an over-the-road truck.

Speaking to reporters gathered for the reveal during the Manifest Vegas 2023 show in Las Vegas, Derek Rotz, DTNA’s director of advanced engineering, said the team did not set out with a clean sheet to investigate every last corner of the vehicle.

“We learned on SuperTruck I which technologies showed promise for production and what did not,” he said. “On SuperTruck II, we focused on what we believe stands the best chance for production.”

Among those left in the basement this time around were the waste heat recovery system, the hybrid electric drive, and wide use of carbon-fiber composite materials for lightweighting.

Rotz said the waste heat recovery system proved to be too complex and too heavy to provide tangible benefits, and it was difficult to package on the chassis. The same applied to the high-voltage hybrid drive. And composites such as carbon fiber are simply too expensive to provide a viable return on the cost.

“That is some of what we learned from SuperTruck I,” said Rotz. “This time, we decided to focus on other core areas instead, like optimized aerodynamics, energy management, and powertrain efficiency.”

Optimized Aerodynamics

Daimler said it achieved a 12% improvement in aerodynamic efficiency with a redesigned hood, bumper and chassis fairings. The truck features active cab side-extenders and a roof spoiler system as well as a camera/mirror system. An active ride-height control system lowers the ride height by a couple of inches to close the gap with the road surface and to lower the overall frontal profile of the truck.

“Because we live in the Pacific Northwest, there's mountains all around us, and we were very much inspired by the way the wind blows across surfaces like snow and sand actually creating the perfect shape,” said the truck designer with the soul of a poet, Jeff Cotner. He’s the design development manager at DTNA. “The wind will tell you the shape that it wants the form to be.”

The hood, bumper and chassis fairings on this truck were designed to complement the existing cab structure and to allow air to flow undisturbed around the truck. The grille, air intakes and doors were redesigned to be as seamless and clean as possible, with no sharp edges to compromise the aerodynamics.

The doors got a redesign, too. A skirt of sorts was added to the bottom of the door that closes the gap between the door sill and the top step. Darek Villeneuve, DTNA’s manager of advanced vehicle systems, said that addition significantly reduced noise inside the cab, which is another way of saying it reduced a lot of air turbulence in that area.

Daimler’s SuperTruck II also features active cab side extenders and a roof spoiler system that deploys at highway speeds. These close the gap between the cab and trailer to just 4 inches. “Aerodynamic Height Control” lowers the truck to just inches off the ground for additional aerodynamic improvements.

Gone from SuperTruck II are traditional mirrors. They are replaced by the MirrorEye camera system with a proprietary camera arm, again, engineered with aero in mind. 

Powertrain Efficiency

Under the newly sculpted hood is a prototype Detroit 13L engine. It’s not certified to any particular emissions standard, because that wasn’t among the objectives of this project. The engine got a lot of attention this time around, especially with air handling and thermal management.

It features two series turbochargers with an intercooler between them to cool the air exiting the first turbo in the interest of increasing the volumetric density of the air entering the second turbocharger. The intercooler is looped into what Daimler calls a split cooling circuit with high and low temperature loops. The low-temperature cooling circuit helps dissipate heat from the exhaust gas recovery (EGR) cooler and a couple of accessory drives, while the high-temp side handles basic engine cooling.

Internally, much work was done to reduce parasitic friction through the use of lighter-viscosity oil and friction-reducing coatings on various surfaces.

“We were trying to use as little oil as possible and use as little energy as possible to circulate the oil through the engine while maintaining its mechanical integrity,” said Villeneuve. “We also went with a thermal barrier coating within the combustion system, in piston heads, the fire deck and the valves — different technologies on those things, but we saw pretty significant improvements.”

The fuel injection system was overhauled to eliminate mechanical losses while the injection pressure was increased to 2500 bar (36,000 psi).

Out back, Daimler is using “adaptive tandem axles” that, with a clutch package located on the forward differential housing, automatically shift from 6x4 to 6x2 at highway speeds. This also allows for load biasing between the driving axle (front) and the would-be tag axle (rear) at highway speed. Coupled with a fresh tire design from Michelin, Villeneuve said the rolling resistance on the high-torque driving tires is reduced by shifting some weight to the extra-low-rolling-resistance tires on the tag axle.

DTNA’s SuperTruck II has a downsped driveline with a 1.75:1 ratio for an engine speed of 950 rpm at highway cruise speed. 

“We have a big difference in rolling resistance between the tag axle and the drive axle,” he explained. “With these technologies working together, we found there's a lot of synergistic effects that really have made a big, big improvement.”

Also new on SuperTruck II is a prototype 13-speed transmission. Overall, Daimler claims a 5.7% improvement in fuel consumption over SuperTruck I.

Energy Management

SuperTruck II features a 48-volt electrical system with lithium-ion batteries, enabling electric “power” steering that adjusts demand as needed at low or high speeds. The oil pump and starter motor are also 48 volts, as is the all-electric HVAC system. It’s a single-circuit AC system rather than the two-circuit system in use today. This, Daimler claims, consumes 50% less energy than conventional AC systems.

Powering some of those systems electrically opens the door to true engine-off operation, which Daimler is calling EcoSail. If the truck is coasting down a hill while the engine is off, features such as air conditioning remain in operation. As soon as power is needed, the engine will restart automatically.

“In testing EcoSail, on certain routes, we saw a 30% operating time when it was engaged and the engine was off,” said Samantha Parlier, Freightliner brand manager. “So, if I was making a 400-mile trip, over 100 miles of that would be going without any energy.”

The 48-volt electrical system is not without its challenges, Rotz told HDT. Power demand is only increasing, and there are a number of obvious applications for 48 volts, but the design and engineering challenges may keep it just outside our grasp.

“There’s quite a bit you can do electrically, but you have to design for safety, too,” he explained. “You have to consider the risks for open circuits, short circuits, and the risk of the 48-volt lines contacting with 12-volt lines.

“We didn’t find the killer app for 48 volts in this project. We found a lot of minor benefits, like controlling the oil pump a little bit better, and more efficient operation of the AC system. They’re all little tiny bits and benefits. They just didn't add together to get the savings you need to justify the cost.”

And he noted 48 volts will likely have a 5- to 10-year commercialization window, at which time demand could have shifted significantly toward fully electric trucks. 

But that’s exactly what SuperTruck is all about. It’s a science project on a grand scale. There are applications for all the technology here, but some of it might not pencil out into a commercially viable product.

The SuperTruck program, co-funded by the Department of Energy, aims to reduce emissions from on-road freight transportation by investigating next-generation technologies with possible commercial applications. Possible is the operative word here.

Watch as Jim Park explains the highlights of the DTNA SuperTruck in this On the Spot video.