Daimler Truck North America revealed its SuperTruck II project at Manifesto 2023 in Las Vegas in early February. The focus was on promising new technologies that could improve real-world operational efficiency.
Photo: DTNA
Daimler Truck North America unveiled its SuperTruck II project in Las Vegas earlier this month. It doubles the freight efficiency of the reference truck, a 2009 Freightliner Cascadia with a DD15 engine.
SuperTruck II builds on the learnings from SuperTruck 1, which was completed in 2015. DTNA’s SuperTruck 1 effort was something of a moon launch, incorporating very advanced technology. SuperTruck II was a little more on the ground. It focused on the most promising core components and systems with real-world applicability—technology that could be more easily integrated into near-future generations of an on-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 didn’t set out with a blank slate to investigate until the last corner of the vehicle.
“We learned at SuperTruck I which technologies were promising for production and which were not,” he said. “In SuperTruck II, we focused on what we believe is the best opportunity for production.”
Among those left in the basement this time were the waste heat recovery system, the hybrid electric unit and the extensive use of carbon fiber composite materials for lightness.
Rotz said the waste heat recovery system proved to be too complex and too heavy to provide tangible benefits, and was difficult to pack into the chassis. The same applies to the high voltage hybrid drive. And composites like carbon fiber are simply too expensive to offer a viable return on cost.
“That’s part of what we learned from SuperTruck I,” Rotz said. “This time, we decided to focus on other core areas, such as optimized aerodynamics, power management and powertrain efficiency.”
Optimized aerodynamics
Daimler said it achieved a 12 percent improvement in aerodynamic efficiency with a redesigned hood, bumpers 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 lower the truck’s overall frontal profile.
The aerodynamic designers left no stone unturned in carving out an additional 12% reduction in drag. Even the doors were treated, in this case with skirts that extend to the top of the entry steps.
Photo: Jim Park
“Since we live in the Pacific Northwest, there are mountains all around us and we were very inspired by the way the wind blows over surfaces like snow and sand creating the perfect shape,” said the soulful truck designer of poet , Jeff Cotner. He is the Director of Design Development at DTNA. “The wind will tell you the shape it wants the shape 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 smoothly around the truck. The grille, air intakes and doors were redesigned to be as clean and seamless as possible, with no sharp edges that compromise aerodynamics.
The doors have also been redesigned. A sort of skirt was added to the bottom of the door that closes the gap between the door sill and the top step. Darek Villaneuve, DTNA’s manager of advanced vehicle systems, said this addition significantly reduced noise inside the cabin, which is another way of saying it reduced a lot of air turbulence in that area.
Daimler’s Supertruck II also features active side cab extenders and a roof spoiler system that deploys at highway speeds. These close the gap between the cab and the trailer to just 4 inches. “Height Control” lowers the truck just inches off the ground for additional aerodynamics.
Since SuperTruck II, the traditional mirrors have disappeared. They are replaced by the MirrorEye camera system with a proprietary camera arm, again designed with aero in mind.
DTNA designers and engineers identified improved tractor aerodynamics, low rolling resistance tires, powertrain improvements and advanced power management as areas of innovation with short paths to market .
Photo: Jim Park
Powertrain efficiency
Under the newly sculpted hood is a prototype Detroit 13L engine. It is not certified to any particular emissions standard, as this was not among the goals of this project. The engine got a lot of attention this time, especially with air management and thermal management.
It has two series of turbochargers with an intercooler between them to cool the air leaving the first turbo in order to increase the volumetric density of the air entering the second turbocharger. The intercooler is connected to what Daimler calls a split cooling circuit with high and low temperature loops. The low-temperature cooling circuit helps dissipate heat from the EGR cooler and a couple of accessory drives, while the high-temperature side handles basic engine cooling.
Internally, a lot of work went into reducing parasitic friction by using 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,” Villaneuve said. “We also went for a thermal barrier coating inside the combustion system, on the piston heads, the fire cover and the valves – different technologies on these things, but we saw pretty significant improvements.”
The fuel injection system was revised to eliminate mechanical losses while the injection pressure was increased to 2500 bar (36,000 psi).
At the rear, Daimler uses “adaptive tandem axles” which, with a clutch pack located in the front differential housing, automatically switch from 6×4 to 6×2 at highway speeds. This also allows for load polarization between the drive axle (front) and tag axle (rear) at highway speeds. Coupled with a recent tire design from Michelin, Villaneuve said the rolling resistance of the high-torque driving tires is reduced by shifting weight to the very low-rolling-resistance tires on the label axle.
DTNA’s SuperTruck II has a reduced driveline with a 1.75:1 ratio for an engine speed of 950 rpm at highway cruising 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’ve found that there are a lot of synergistic effects that have really made a big, big improvement.”
Also new to SuperTruck II is a prototype 13-speed transmission. Overall, Daimler claims a 5.7% improvement in fuel consumption over the SuperTruck I.
DTNA collaborated with Michelin in the development of new tires designed specifically for adaptive tandem axles. The XM 586 model tires reduce vehicle energy consumption and are said to have exceptional wear characteristics.
Photo: Jim Park
Energy management
SuperTruck II features a 48-volt electrical system with lithium-ion batteries, which enables electric 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 is a single-circuit AC system instead of the two-circuit system used today. This, Daimler claims, consumes 50% less energy than conventional AC systems.
Electric powering some of these systems opens the door to true engine-off operation, which Daimler calls EcoSail. If the truck goes down a hill while the engine is off, functions such as the air conditioning will continue to operate. As soon as power is needed, the motor will restart automatically.
“When testing EcoSail, on certain routes, we saw 30 percent uptime when it was on and the engine was off,” said Samantha Parlier, Freightliner brand manager. “So if I were doing a 400-mile trip, more than 100 miles would go without any power.”
The 48-volt electrical system is not without its challenges, Rotz told HDT. Demand for power is only increasing, and there are a number of obvious applications for 48 volts, but design and engineering challenges may keep it out of our reach.
“There’s a lot you can do electrically, but you also have to design for safety,” he explained. “You have to consider the risks of open circuits, short circuits, and the risk of 48-volt lines coming into contact with 12-volt lines.
“We didn’t find the killer application for 48 volts on this project. We found a lot of minor benefits, like slightly better control of the oil pump and more efficient operation of the AC system. These are all small details and benefits. Just they didn’t add up to get the savings you need to justify the cost.”
And he noted that 48 volts will likely have a commercialization window of 5 to 10 years, by which time demand could have shifted significantly toward all-electric trucks.
But that’s exactly what SuperTruck is all about. It is a large-scale scientific project. There are applications for all the technology here, but some of them may not make it into a commercially viable product.
The SuperTruck program, co-funded by the Department of Energy, aims to reduce road freight emissions by researching next-generation technologies with potential commercial applications. Possible is the operative word here.
