Truck & Off-Highway Engineering – June 2019

TRUCK & OFF-HIGHWAY ENGINEERING June 2019 19

ALL IMAGES: PERKINS

solution for a telehandler might not be the same as for a road roller,

which might not be the same for an excavator or a wheel loader.

There’s quite a range of optimal solutions.”

Perkins highlighted three different hybrid power solutions at bauma,

all based on the company’s Syncro 2.8-L Stage V engine and all gener-

ating 75 kW (100 hp) of peak power to provide a direct comparison.

The first is a hybrid-electric setup using a motor generator with the

engine, lithium-ion batteries to store up to 6 kWh, and 48-V electrics.

Long-duration energy storage makes this a suitable option for ma-

chines with less-predictable operating cycles, “but it likes to release

energy quite slowly,” Lythgoe explained. “So if you want to release a

lot of energy, you need a big battery, which becomes hard to pack-

age in a machine and gets expensive.”

A mechanical hybrid stores energy in a high-speed flywheel that

can be delivered back to the machine. This setup is particularly useful

in hybridizing machines that run a cyclic operation and need very

intense bursts of additional power. Installation size is another benefit

compared to hybrid-electric: “In a very small space you can package

this into an existing machine,” he said. But the system has an energy-

storage capacity of only 0.05 kWh.

The third solution is a hydraulic hybrid that stores energy (0.04

kWh) as high-pressure hydraulic fluid in accumulators, which could

be the most practical and cost-effective hybrid solution for some

machines, Lythgoe said.

“Many machines already have lots of hydraulic architecture in

place—pumps, valves, motors, electronic controls—so the effect on

the machine will be quite minimal and quick to implement. Another

thing is it’s technology that everybody understands,” he said.

“However, if it’s not a cyclical operation, it’s not going to help you.”

The market will decide

The solutions don’t end there. According to Lythgoe, there are eight

different hybrid architectures that could be viable for one type of

off-highway machine or another, including “several different flavors

of electrical hybrids,” he noted.

Micro hybrids provide a small amount of electrical boost with not

much recovery but in an inexpensive package. Series hybrids only

deliver power from an electric motor run by a battery or a gasoline-

powered generator—or versions that integrate renewables. “For fixed

installations in telecoms, for example, you could integrate solar pan-

els or wind,” Lythgoe said.

Parallel hybrids have a much more-sophisticated transmission to

be able to switch between power sources: the electric motor and in-

ternal combustion engine, which can provide power simultaneously.

Pure electric machines are another option, as is a “limp home” range

extender that incorporates “an undersized engine to get out of trou-

ble or to just work that extra hour in the day,” he said.

“Even in the electrical options, there’s quite a lot of differences in

voltages—48 volt or 400 volt, 600 volt or 700 volt. Some are AC and

some DC, and these are fundamental questions to how you build a

machine, how much it costs, how efficient it is, and also what kind of

technician you need to maintain it.”

Recharging in remote locales poses a challenge. “Some cases it will

be solvable,” he said. For example, in small wheel loaders commonly

used in agricultural applications, charging points can

be placed at fixed points on a farm where machines

always return. “But there’ll be other [applications] that

are almost impossible to resolve. If you are operating

the excavator that is building the electrical substation,

it’s hard to see how you’d get around that.”

Lythgoe noted that “real technology” is currently run-

ning in its test cells, but he could not share which custom-

ers and which machines are involved. And plans for tech-

nology rollout will be guided by market demands, he said.

“We’re going to listen to our customers and see

where they want to go, where they’re being driven by

their stakeholders. If it’s, ‘Hey, let’s get fuel economy

now,’ then it’s going to be one set of technologies. If

it’s, ‘Let’s take a slightly longer view but get to zero

tailpipe emissions,’ then it’s going to be a different set

of technologies. We have to be guided by what the

market wants rather than what we want to sell.”

EXECUTIVE VIEWPOINTS

Operating cycles and packaging constraints will help to decide

which option is suitable for a particular construction machine.