“How do you get the 50% aero reduction and improvement? You have to pay attention to details.”
That’s Keith Brandis, vice president of system solutions and partnerships for Volvo Trucks North America, showing reporters the Volvo SuperTruck 2 in its first public appearance during the American Trucking Associations’ 2023 Management Conference & Exhibition in Austin, Texas.
The truck, said Volvo, offers “a glimpse at styling and engineering cues for future generations of trucks.”
Rather than focusing strictly on miles per gallon, Volvo focused on freight efficiency.
The SuperTruck 2 program, a public-private partnership with the U.S. Department of Energy, tasked OEMs with achieving a 100% freight efficiency improvement over their submitted 2009 baseline. Volvo Trucks not only achieved the DOE objective but exceeded even its own higher goals, with a 134% increase in freight efficiency.
Aerodynamics and lightweighting were key strategies.
While Volvo's SuperTruck 1 was a slightly modified version of a VNL 670 cab, SuperTruck 2 boasts a brand-new cab design, including a radically different windshield.
The cab is wedge-shaped from front to back, including a raked and wraparound windshield, a front end designed around a downsized cooling package, and an adjustable ride height that allows for better aero at higher speeds.
“Starting from the hood working our way back, we were able to have a sloped, wraparound windshield, a wedge shaped cab, closed in the trailer gap, all the cab aerodynamics, the cab fairings, the chassis fairings… all the way to the back of the trailer with the boat tail,” said Eric Bond, principal engineer, in a walkaround of the truck at the show for reporters done with Brandis.
Volvo also replaced the traditional hood- and cab-mounted mirrors with a streamlined camera monitoring system to reduce the drag by more than 4%.
Probably the biggest technical challenge, Brandis said, was the windshield.
“You’ve never seen a windshield like this,” he said. “The rake on the windshield, the curvature of the windshield, moving the A-pillars backwards and sloping them, meant that it was a complex piece of glass, that had to continue to meet the optical qualities the driver needs to see on the road ahead.”
Another area of focus was keeping the truck low to the ground.
“How do you keep the air from spilling under the vehicle, creating drag, requiring more fuel?” Brandis said. The front suspension system was lowered by 2 inches and the truck uses 19.5-inch tires (which also mean less weight and reduced rolling resistance).
There’s even an air scoop in the front of the bumper that helps move the air around to the outside and create a sweep on the outside of the wheel well for additional aerodynamics, Bond explained.
The chassis fairings on the truck on display at the show were virtually touching the floor. The full air-ride suspension allows the truck to raise up to 6 inches higher during low-speed maneuvering, while it lowers at highway speeds for optimum aerodynamics. And, engineers said, the fairings are designed to be sturdy, with a flexible strip at the bottom.
Volvo Trucks worked with Wabash to create a custom, lightweight aerodynamic trailer with an optimized aerodynamic shape of the full truck and trailer to appear as one seamless unit. The entire tractor-trailer combination showed 50% lower drag than Volvo Trucks’ 2009 baseline and was a 20% improvement over Volvo Trucks’ SuperTruck 1.
Lightweighting the SuperTruck
In addition to the aerodynamics advancements, there was a tremendous focus on lightweighting.
“We were able to go ahead and take a ground-up approach,” said Eric Bond, principal engineer, starting with the axle configuration. The SuperTruck 2 is a 4x2 configuration, which is not common in the U.S. but is frequently used in Europe, using fewer axles for the same payload.
“A 4x2 that’s capable of 65,000 pounds,” Bond said. “There’s a lot of lightweighting that had to go into it as a result.”
The result was a reduced curb weight of 27,000 lbs. for the combined truck and the trailer.
The truck was designed so it could be applied to a 6x2 or 6x4 configuration, but that was not part of the specific demonstrator validation for this program. The shorter cab design is lightweight and paired with an aluminum chassis that uses a lightweight optimized drive axle system with a single composite driveshaft.
“Every inch of this truck, very detailed design, a lot of engineering went into lightweighting this as much as possible,” Bond said, “to get us the payload. In addition to the aerodynamics and in addition to the fuel economics we had, this vehicle is capable, even with 65,000 pounds gross combination weight, of about 38,500 pounds of payload.”
“We came up with an aluminum framerail, aluminum crossmembers, special suspensions,” Brandis said, “even counting the number of bolts that we have on the chassis, to take out every pound that we could possibly find.”
One challenge with an aluminum framerail is that you can’t weld to it, Brandis said. Using 3D-printing technology, engineers created brackets for fastening the chassis fairing, as well as for the routing and clipping and cabling.
“Our downsized, rightsized, technologies for the powertrain, which also enabled the aerodynamics,” Bond said. “We were able to go to a lower, smaller, cooling package that gave us really that good aerodynamic shape on the front of the truck.”
The SuperTruck 2 is powered by an 11-liter, 325-hp base production engine, but Volvo engineers made a number of changes with pistons, a fixed-geometry turbo, thermal and friction reduction, and a smaller exhaust aftertreatment system.
“A lot of the technology we did with this engine here was directly applied to what we have on the 13 liter product line,” Bond said.
One key to being able to use a smaller engine is the 48-volt micro hybrid system, which is an integrated starter-generator.
Many of the engine accessories that normally would be belt driven or gear driven are now powered by this 48-volt system. That helped to make the whole engine and driveline more efficient.
The micro hybrid system also provides power for driver comfort features. That includes an all-electric HVAC system capable of running off the batteries for 12 to 14 hours without idling.
Most trucks in the market right now don’t have 48-volt electrical systems. However, Volvo’s not the only OEM to explore 48-volt systems in their SuperTruck projects. Daimler Truck North America’s SuperTruck II features an innovative 48-volt electrical system as well, and they were exploredin the first round of SuperTruck projects.
What About Engine Brake Thermal Efficiency?
One thing Volvo didn’t achieve with SuperTruck 2 was the goal of 55% engine brake thermal efficiency.
The team developed a driveline optimized for freight efficiency, applying advanced technologies to the 11-liter engine platform, which was demonstrated on-road in the SuperTruck 2.
The team also worked on a 13-liter powertrain optimized for brake thermal efficiency, which was demonstrated in a test cell, which allowed them to test additional concepts and push the limits further.
“Although we fell short of the 55% target, this dual-path approach provided the ability to develop and experiment with many new technologies without jeopardizing the [freight efficiency] optimized SuperTruck 2 demonstrator,” said a Volvo spokesperson when asked about the BTE results.
“You can create the most fuel-efficient powertrain, regardless of propulsion method, but without proper aerodynamics you won’t achieve the freight efficiency desired.”
On the Way to Electric Trucks
Much of the R&D work done on the SuperTruck 2 program is also applicable to SuperTruck 3, which focuses on electric trucks.
Lightweighting, for instance, is important to offset the payload penalty of heavy batteries. Aerodynamics, just as it can reduce fuel use in a traditional truck, can improve range in a BEV.
Converting engine accessories to electric-driven is another factor when going to electric propulsion instead of diesel.
In addition, Brandis explained, “There’s going to be a different purpose for the cooling. Instead of cooling an engine, we still have to cool all the power electronics.
“But let’s see how we can use that space, which was an engine, and now put more battery packs, to get the extended range that we’re looking for.”
More batteries, however, mean even more heat.
“Especially when you’re talking megawatt charger levels, that creates a tremendous amount of heat,” Brandis says. “So we have to cool the cables. They’re liquid-cooled cables, including the ones that go to the charger.”
The DOE’s SuperTruck 3 program has awarded more than $18 million for Volvo Group North America to develop a 400-mile-range Class 8 battery-electric tractor-trailer with advanced aerodynamics, electric braking, EV-optimized tires, automation and route planning. A megawatt charging station will be developed and demonstrated.