Volvo adds hybrid power to SuperTruck concept
Commercial trucks may not be as plentiful as cars in the US, making up just 7 percent of vehicles on the road, but they consume 25 percent of the fuel due largely to an average fuel economy of 6 mpg, according to the Union for Concerned Scientists. Volvo has sought to do something about this with its SuperTruck concept, which has now been fitted with a prototype hybrid powertrain that would reduce fuel consumption by 5 to 10 percent by allowing the diesel engine to shut off up to 30 percent of the time.
Volvo started its SuperTruck concept project in 2011, with testing beginning in 2015 ahead of an official unveiling last year. Prompted by a US Department of Energy challenge, the goal of the project is to find ways to improve freight efficiency by 50 percent, mostly by improving aerodynamics and reducing weight. Under the same DOE challenge, Freightliner has also been working on its own SuperTruck.
By adding the hybrid powertrain system, energy can be recovered when the truck is braking or driving downhill, which then allows the vehicle to go all-electric on level or low gradient roads for up to 6.2 miles (10 km). Combined with previous improvements to the body of the vehicle, both the fuel consumption and CO2 are reduced by about 30 percent.
Some of those prior improvements included using a chassis made almost entirely out of aluminum, which helped reduce the trucks overall weight by 3,200 lb (1,450 kg). To lower drag and turbulence, fairings were added that covered all the wheels except in the tractor's front, with spoilers added to the back of the trailer. Side-view mirrors were replaced with cameras. All of this has helped the SuperTruck improve its fuel efficiency by 70 percent compared to a baseline model (the 2009 Volvo VNL 670), while surpassing 12 miles per gallon in road tests.
Another new feature to the SuperTruck is Volvo's hybrid-specific I-See driver-assist system, which uses GPS data and digital mapping to analyze the approaching terrain. The software uses this info to choose the most efficient use of both the electric motor and engine in regards to the topography, while optimizing energy recovery.
Though the actual SuperTruck itself may never be put in service, some aspects could make it through to production models. In fact, aerodynamic elements can already be found on current models.
Source: Volvo Trucks
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The hot side of the Stirling can also incorporate (catalytic) diesel-emission controls.
Waste heat from diesel engine cooling (and the cool side of the exhaust energy recovery) could be concentrated to run another Stirling engine and gen-set to contribute more usable energy back to the rig.
You could even run an expansion engine (like on an old steamship) to capture a bit more power from the last bit of exhaust before it's released to atmosphere but there's likely little left to gain here for the added complexity.
Complex, sort of, but there's enough room on a large highway tractor to incorporate all these items and the control systems for them.
Estimated efficiency improvements are significant. If an efficient diesel rig can get 10 mpg, the exhaust-heat-Stirling could potentially add another 3 to 4 mpg. That's a pretty big improvement and worth incorporating into long-haul tractors where steady highway speeds would provide a constant and reliable heat source to drive the Stirling gen-set. A 3-way-hybrid of this sort would be the ultimate way to get the most usable energy from a combustion engine driveline.