The case for 48 volts in commercial vehicles
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The ReAX EPS from ZF is a 48V prototype of a fully electric steering system for commercial vehicles that eliminates the need for hydraulics and associated peripheral components. Its electric motor offers complete servo power up to 70 N·m (52 lb·ft). (image: ZF)

The case for 48V in commercial vehicles

Higher voltage architectures allow for more efficient power generation and distribution, according to Jim Bevan, Mechatronics Power Systems Manager for Daimler Trucks North America. “Making this change also allows us to explore energy recovery technology, turning the vehicle into a scaled-down hybrid. This can contribute to fuel savings, as well as provide more efficient power distribution to engine accessories and other electronics on the vehicle,” he told Truck & Off-Highway Engineering.

Bevan noted that while 24V systems have been in place in Europe for some time inside some commercial vehicles, his company’s evaluation of North America has not led them to implement it here, while they continue to explore 48V architecture and solutions.

The main advantage of a 48V system may lie in its cost to benefit. “Generally, we get 80% of the benefit for 20% of the cost,” compared to higher voltage alternatives, said Carl R. Smith, Commercial Manager, Sales, Applications Engineering and Customer Support for Eaton eMobility.

A 48V system is not considered a shock hazard to humans. “Anything above 60V requires special cabling and wiring and you get into more regulations. That is one reason why 48V is less expensive to implement,” Smith explained.

Another reason is the battery in the system. As an integer multiple of the current 12V systems, engineers can put four dependable lead-acid batteries in series, often eliminating the need for more expensive batteries.

How does it work? Higher voltages make it easier to increase power to components without increasing current. Higher currents mean more copper and thus more weight and expense in cabling and more loss in transmission. 48V might be in a sweet spot.

“12V systems practically top-off at 3.5 kW, but many components that are useful in autonomous driving or fuel economy improvements operate around 5 kW,” Smith said—too much for practical 12V systems. A 400 or 800V system could provide much more power—more than needed—for much more cost.

“For example, a strategy to increase fuel economy and improve emissions is to incorporate engine off/coast,” explained Smith. “If you do that, you need a way of keeping critical systems running that were once belt-driven from the engine. These include safety systems, cooling systems, braking, steering, or air-conditioning,” he said. All of these components are in that 48V sweet spot.

Components driven by 48V electric motors also give vehicle designers more flexibility in packaging when compared to their belt-driven alternatives like the front-end accessory drive (FEAD). Now, engineers can package components like cooling fans off the front of the engine to improve aerodynamics and fuel economy. FEAD could disappear.

Smith believes that 48V will begin an initial adoption in the commercial truck and agricultural equipment markets within five years or less. In fact, some elements are here already. For example, John Deere introduced in 2015 a row-crop planter driven by an electric motor operating at 56V.

This ExactEmerge row unit increases speed and eliminates hydraulic lines needed in traditional seeders, according to Deere. The company boasts that it gives corn and soybean producers the ability to plant at 100% increase over non-electric units, maintaining superior seed placement.

Another company making investments in higher voltage components is ZF. Citing many of the same motivations mentioned above, ZF announced in a June 2018 press release the reveal of its ReAX electric power steering system. The ReAX EPS prototype for commercial vehicles “can simplify and accelerate the advance of electrification, including 48V on-board vehicle power supply systems and steer-by-wire options, and do so with high efficiency and reliability,” Mitja Schulz, head of CV Steering Systems at ZF, said in the release.

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