Hydraulic hybrids from Eaton are stiff competition for electric hybrid alternatives.

Electrified off-highway powertrains search for marketing power

Electrified powertrains have seen success in commercial applications like buses and small vehicles, but in many fields, they’ve seen only limited success. Today’s low fuel prices are not helping marketers expand the niches where hybrids provide a cost-effective solution.

Most electric off-highway vehicles are relatively small vehicles that have small power requirements compared to some construction and agriculture behemoths. Hybrids fit more use cases.

“For non-road mobile machinery applications, a pure electric mode of operation is only relevant for small machines, less than 19 kW,” said Kiran Govindswamy, Powertrain Director at FEV North America. “Only hybrid concepts, from micro to mild and full hybrids, are considered to be feasible for most applications. This is fundamentally driven by high add-on costs for batteries as well as time needed for recharging the batteries.”

In all vehicle classes, electrified powertrains face competition from hydraulic hybrids. Battery packs take a fair amount of space compared to hydraulic components. Automotive hybrids are driving advances in batteries, but many developers feel it’s easier to use battle-tested hydraulics than to revamp systems on existing product lines.

“Adding an electric power architecture adds cost and complexity that the base machine doesn't normally have,” said Randy Peterson, Chief Engineer, Hydraulics, at Caterpillar Advanced Components & Systems Division. “The power density (size) advantage for hydraulics over electrics is still in the neighborhood of 10:1 or more, making packaging electrics a challenge.”

Many usage models require quick bursts of power that can be difficult to provide with electric motors. Battery discharge and charging rates can work against electrics in many environments.

“As battery technology continues to improve, the ability to store and use energy becomes much more attractive,” said Steve Zumbusch, Technology Development Director for Eaton’s Hydraulics Group. “If the rate of energy consumption (power) becomes high, then the battery technology becomes challenged with being able to rapidly store and discharge energy fast enough to be effective. Hydraulics on the other hand, have a very distinct advantage in using technologies such as accumulators that can be charged and discharged extremely fast, providing very high power levels.”

Though battery power has limits, its role may still expand. Advances in automotive are driving down overall system costs, and there’s no guarantee that global oil prices will remain low. Potential regulatory restrictions are also prompting a lot of research into hybrids.

“The low cost of fuel has negatively influenced the payback period,” Govindswamy said. “With the exception of large excavators, electrified powertrain payback times currently remain rather poor. Considering significantly reduced hybrid add-on costs as well as a slight increase in fuel price, hybridization with reasonable payback periods are expected to become feasible in the future.”


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