Should Heavy-Duty Truck Owners Consider Mild-Hybrid Systems?


2014 Peterbilt 579

2014 Peterbilt 579

As carmakers work to meet stricter global emissions standards, many regular internal-combustion cars will adopt some degree of electrification--including systems with mild-hybrid aspects.

A "mild hybrid" powertrain isn't capable of using electricity alone for propulsion.

But it offers more aggressive engine start-stop, added electric torque to assist the engine, and electrified accessories, all to boost the fuel economy of conventional powertrains.

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There's been a lot of chatter about future applications of these systems for cars, but what about other vehicles that could use an efficiency boost?

Heavy-duty trucks cover more miles than passenger cars--with much worse--fuel economy.

While full-hybrid powertrains remain problematic, could mild-hybrid systems be a good fit?

Daimler Trucks North America SuperTruck

Daimler Trucks North America SuperTruck

That's the case made in a recent SAE International blog post, contributed by powertrain-research firm AVL.

Conventional hybrid powertrains are considered a non-starter for large trucks because of their much higher initial cost--which owners may not be able to balance with fuel savings.

Unlike city buses--many of which already feature hybrid powertrains--heavy-duty trucks are driven mostly on highways, with less stopping and starting.

They're also owned for shorter periods of time, so there's less chance to recover the purchase price in fuel savings.

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Much simpler mild-hybrid systems would cost less, but still deliver meaningful fuel-economy improvements, the post's authors argue.

Mild-hybrid trucks would feature electric auxiliary systems, powered by energy recovered through regenerative braking.

Switching to electric power steering, for example, yielded a 0.8-percent increase in fuel economy during a simulated Stuttgart-Hamburg, Germany, round trip.

Mack Pinnacle series

Mack Pinnacle series

Overall fuel savings of two to four percent are possible with mild-hybrid systems, the authors say.

That may not sound like a lot, but even small improvements in the least-efficient vehicles add up to significant fuel savings.

They may also become necessary if a proposed new round of U.S. fuel-efficiency standards becomes reality.

MORE: Obama Tells EPA To Set Next Heavy-Duty Truck Fuel-Efficiency Rule (Feb 2014)

Manufacturers already have to achieve a 10- to 20-percent increase in fuel economy by 2018.

But President Barack Obama wants regulations mandating further improvements between 2019 and 2025.

Those bring large trucks in line with Corporate Average Fuel Economy (CAFE) standards for passenger cars, which already run through 2025.

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