Fleet Maintenance - 14

increasing the life of those tires. Additionally, data
from Link Manufacturing and Mack Trucks shows
that tire life with a 6x2 liftable pusher can be
improved by up to 20 percent compared to a 6x4.

6x2 specification advice

How electric
axles can further
enhance fuel
efficiency with 6x2
configurations
Electric axles, known as e-axles, could be
used in conjunction with tag or lift axles
pending application needs, say experts at
driveline and brake supplier Meritor.
As the industry continues discussion
around vehicle electrification, e-axles are
a means to electrify a system on a traditional diesel engine while providing better
fuel efficiency and less moving parts. The
same design used on a hybrid truck can also
be spec'd on a fully electric drivetrain.
An e-axle system consists of an electric motor,
transmission, and a drive axle. How does it work?
"An e-axle uses an electric motor to assist
or be the source of propulsion of the vehicle," Meritor experts say. "The electric
motor takes the place of the ring gear and
associated gearing in the axle housing contained as one power-dense package."
This design provides flexibility and a more
seamless integration for truck manufacturers
when spec'ing e-axles like Meritor's eCarrier.
In a conventional powertrain, the torque
comes from the engine, passes through the
transmission and driveline, and travels up to
the axle and wheels, enabling the vehicle to
propel. With an e-axle, an electric motor and
a transmission with fewer gears take the place
of the conventional engine and transmission.

14 Fleet Maintenance | April 2020

»Hendrickson's Optimaax liftable forward
(pusher) axle design automates the lowering
and lifting of the axle by sensing load
capacities; no driver intervention is needed.
Photo courtesy of Hendrickson

ured with a 6x2 pusher such as Hendrickson's
Optimaax, traction can be improved.
"We have also heard from our fleet customers
that the ride is better, especially when lightly loaded or in a bobtail," Williamson says.
As Van Den Brink explains, the drive axle
remains behind the fifth wheel in a pusher
configuration, which increases tire friction. Then,
when the tractor has the right control system,
the driver can maximize load on the single drive
axle. "Users of our 6x2 pusher have actually told
us they get better traction than a 6x4 because
they are getting that maximum load on one drive
axle," Van Den Brink says.
Ploger Transportation's fleet includes both 6x4s
and 6x2s on Volvo and Mack trucks. Morrow says
the weight distribution logic that is part of the
Volvo system has made all the difference.
"Not only does the system know when it's time
to lift the axle, but it also has an algorithm to
help bias weight to the drive axle," Morrow says.
That's how a 6x2 liftable pusher axle can provide
enhanced traction.
With a tag axle, on the other hand, the drive
axle is in front which makes it difficult to achieve
optimum weight transfer.
"Traction and tire life really suffer," Morrow adds.
Speaking of tire life, liftable pusher axles can
also reclaim some of that negative stigma associated with 6x2 tags. Weight transferring, as Morrow
just explained, is an important part. The other part
is that with tag axles, all four rear tires are on the
road at all times, whereas liftable pushers take
two tires off the road when not needed, therefore

All in all, with the correct logic and torque,
Morrow believes a 6x2 liftable pusher axle is
on par or better than a 6x4 in just about any
on-highway application. Fuel economy has been
the biggest benefit.
"We're getting another half-mile per gallon at
least," Morrow says.
Some of Morrow's fuel savings used to go right
into tire replacements. Now he has figured out how
to reduce wear and extend life so that isn't necessary.
"We've learned to avoid using wide-based tires
on 6x2s because all the power and torque are
going through just two tires," Morrow explains.
"Instead, we use tires with moderate rolling resistance and more traction."
Along with tires, Morrow says he has learned a
few other lessons about how to properly specify a
tractor-trailer with a 6x2 pusher axle:
Ü Since the goal is to get the lift axle off the
ground as much as possible, go with a heavier
(i.e. 14,000 lbs) front steer axle.
Ü Pay attention to engine size and weight. An 11L
or 13L engine can provide power and torque on
par with a 15L engine, and the lighter weight
engine will help when it comes to weight transfer and lifting of the axle.
Ü With a 6x2, numerous oil and gear sets are
eliminated, therefore power transfer to the
drive axle is more efficient. Thus, 450hp will
pull just as well as 500hp.
Morrow says it is also a good idea to consider a
transmission with a crawler gear - even if you're
in a general freight application.
"You need 25 percent of gross combination
vehicle weight on the drive axle to maximize traction," Morrow explains. "It's easy to do that when
you're light and the pusher axle comes up. But
when you're heavy and need to maintain legality
on the axles, the axle drops, and you have a hard
time meeting that 25 percent on the drive axle.
Maybe you only get 18 percent. To compensate, a
crawler gear will help you get started on slippery
surfaces with a heavy load."
Dana's Mastroianni says fleets often develop
their own preferences on how they like to specify
their vehicles for 6x2 axles.
"Some try to lightweight the upfront area of the
truck, maybe going with a slightly smaller engine,
just to balance things out more favorably so they
aren't as front-end heavy," Mastroianni relates.
"Some fleets prefer wide-base singles while others
prefer dual tires. Some like torque-reactive suspensions while others do not. There are all kinds of
tweaking fleets can do with 6x2s to get the most
favorable vehicle dynamics they are looking for."
In the case of Dana 6x2 axles, Mastroianni
says the company offers various features that
help support a truck being configured in the right
way to maximize traction. Examples include wider
axle housings to provide the right track width to
support the vehicle and thicker wall housings to
accommodate various weight ratings.

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