20 E-AXLES
a range of confi gurations that could include combustiononly
two-wheel drive, hybrid all-wheel drive (with the
addition of an e-axle) and electric-only drive on either
axle (or indeed both).
This multitude of options raises some interesting control
challenges, Fliscu points out: “If you have two separate
drive systems, you need to look at how you manage
the torque split to maximise safety, performance
and effi ciency. You don’t want one end dragging
the other. Regenerative braking also becomes
quite interesting, because recovering energy on
the rear axle sometimes poses stability issues.
One approach we adopt at AVL is to develop the
supervisory controller to the point where it is
largely agnostic to the layout of the hybrid system.”
The simplicity that comes from a single, integrated
unit is particularly useful when it comes to vehicle
assembly, as Alan Cherrington, chief operating offi cer
VehicleDynamicsInternational.com • November/December 2019
at Integral Powertrain explains, “The OEMs’ supply
chain requirements often dictate that they would like a
complete integrated unit that’s ready to fi t into a vehicle.
That makes the build process on the production line a lot
neater than trying to bring together disparate elements
from different companies.”
Integral Powertrain supplies the motors for a joint
project with McLaren Applied Technologies and Hewland
Engineering. The end result is a single unit ready to lift
into the chassis with just four mounting bolts, two wires
for the DC supply, and a couple of cooling connections.
There are potential challenges when servicing a heavily
integrated unit, but Dr Stephen Lambert, HEV product
manager at McLaren Applied Technologies, doesn’t believe
they pose an issue for e-axles.
“Historically in the automotive industry, integrated
designs have tended to make things more diffi cult with
regard to serviceability,” he says. “If you had a
failure in one component, it could potentially be
harder to rectify, particularly if you had to service
the entire integrated system. But with the reliability
and comparative simplicity of electric vehicle
drivetrains there are no real servicing requirements,
apart from basic checks and transmission fl uid
changes. This opens the door to higher levels of
integration and innovative new products.”
In particular, he explains, the biggest advance
seen in recent years has been the addition of power
The 48V option
When 48V electrification is mentioned, it’s generally in the context of a mild hybrid
setup, aimed principally at coping with the demands of power-hungry auxiliaries.
However, some see a great deal more potential for these low-voltage concepts.
At last year’s North American International Auto Show, Schaeffler presented
its High Performance 48V concept vehicle (pictured above), which combined a beltdriven
starter generator with a rear-mounted e-axle. This system was capable of
delivering 20kW and as much as 2,000Nm at the wheels, providing electric-only
running at speeds of up to 21mph (35km/h) and a ‘sailing’ function at speeds of
up to 43mph (70km/h) via a two-speed transmission. The company notes that the
majority of braking energy released on the WLTC cycle could be captured and stored
in the battery using this system.
Elsewhere, Magna’s eRAD Traction Assist is a 48V e-axle designed to provide
a limited amount of pure electric driving functionality, as well as all-wheel-drive
support in low-friction conditions.
BELOW: McLaren Applied
Technologies’ combined
traction unit is an e-axle
system that takes energy
from HEV or EV battery packs
“With the reliability and comparative simplicity of electric
vehicle drivetrains there are no real servicing requirements,
apart from basic checks and transmission fl uid changes.
This opens the door to higher levels of integration and
innovative new products”
Dr Stephen Lambert, hybrid and EV product manager at McLaren Applied Technologies
/VehicleDynamicsInternational.com