NEWS
24 APRIL 2 019 AUTOCAR.CO.UK 19
IF LAST WEEK’S column was anything to
go by, EV motors are far more interesting
than they look. Once people get their heads
around them, they may hold the same
fascination that engines have enjoyed since
they were invented. The electric machines
(the correct name for motor-generators) in
EVs today take various forms electrically,
but the one thing they have in common is
that they are all radial fl ux machines. Flux
is the scientifi c name for the direction takenby the magnetic fi elds but, in simple terms,
it means they are cylindrical in shape with a
rotor spinning inside a cylindrical stator.
There is, however, another type of electric
machine emerging, and it’s one that some
car makers are looking at intently, especially
for integrating with a combustion engine to
hybridise it, or tacking onto a small engine
to make a range-extender generator. It’s the
axial fl u x ‘ bi s c u it t i n’ mot or.
If biscuit tin sounds derogatory, it isn’t
(and come on, who doesn’t like a Hobnob?).
It’s the simplest way to describe the shape:
short in length and large in diameter. This
is useful because it means that in some
applications they can use space more
effi ciently than a radial fl ux motor, such
a s w he n s a nd w ic he d b e t w e e n a n e n g i ne
and gearbox on a transverse engine. They
have other important advantages, such as
the ability to generate more torque than a
radial fl ux equivalent.
Whereas the rotor (which rotates) of
a conventional radial fl ux machine is
relatively small in diameter because it is
housed inside the stator (which remainsstatic), the rotor and stator of the axial fl ux
machine are like two large dinner plates
facing one another. So both plates’ magnets,
the fi elds of which interact to generate
torque and spin the rotor, are set much
further away from the motor’s driveshaft.
Because of that, the force they produce
has more leverage on the main shaft. That
means more torque, or the same torque for
less power consumption.
A good way to visualise that is to think of
the steering wheel on a car. Imagine taking
the wheel off and grasping the steering
THE HUB OF THE MATTER
column with your
hand. It would
be pretty diffi cult
to turn. Moving
the effort you’re
applying further away
from the column – by
using a wheel – gives you more leverage, or
turning force. The same thing happens with
an axial fl ux motor.
More companies are developing thetechnology, and one of those in the forefront
is the Oxford-based fi rm Yasa. Its P
electric machine can be sandwiched
between an engine and transmission in a
‘P2’ hybrid confi guration or be used stand-
a lone. A t ju s t 80 m m t h ic k , t h i s sl i v e r of a
machine weighs only 24kg, develops peak
power of 215bhp (160kW) and 273lb ft peak
torque. Yasa also has a complete electric
drive unit (EDU) concept comprising a
motor, controller and two-speed powershift
automatic transmission. The motor itself
produces peaks of 402bhp and 368lb ft and
yet it weighs in at just 85kg. That compares
pretty favourably with the average four-
cylinder engine, which weighs around
150kg without the transmission.
I t ’s o n l y a m a t te r of ti m e b efo r e e l e c tr i c
machines move to the wheels, freeing upspace and possibly changing the way
cars look. The axial flux
design lends itself
perfectly to this.
US firm Protean
Electric has
yet another
design, its
‘inside out’
permanent
magnet motor,
with the stator
on the inside
and rotor on
the outside.
THE EMERGING ELECTRIC TECH
THAT’S SET TO DRIVE OUR FUTURE
Axial
flux motors like
this Yasa P400 series
can be integrated with
combustion engines for
hybrids or used alone for EVs.
It was used to power the
Jaguar C-X75 concept
and the Koenigsegg
Regera.
UNDER
THE SKIN
JESSE CROSSE
SPECIAL KIA STINGER GETS DRIFT MODE
The new US-only Kia Stinger
GTS packs a new drift mode
that’s likely to appear on
standard Stinger GTs when
the car is updated in 2020.
The limited-edition GTS
features a newly developed
all-wheel-drive system that
includes the drift mode.
Although all-wheel drive is
available in some markets,
only rear-drive Stingers are
currently sold in the UK.Kia says the new version
of the Stinger’s all-wheel-
drive system is “peppered
with rear-wheel-drive DNA”.
Called D-AWD, it’s intended
to close the gap in behaviour
between existing all-wheel-
drive and rear-drive GTs.
The D-AWD system has a
mechanical limited-slip rear
differential. There are three
different drive settings,
including a drift mode that
sends 100% of power to the
rear wheels and holds gears
without shifting up.
The Stinger GTS uses
the same powertrain as the
standard Stinger, a 3.3-litre
twin-turbo V6 with 365bhp
and 376lb ft paired to an
eight-speed automatic ’box.
The special-edition car,
which is limited to 800 units,has bright orange paint
and uses carbonfibre parts
around the ‘tiger nose’ grille
and side vents. Inside, the
steering wheel and centre
console are trimmed in
Alcantara. A sunroof and
Harmon audio also feature.
The GTS with D-AWD costs
from $46,500 (£35,730),
$13,600 (£10,450) more
than the US starting price. In
the UK, the Stinger is priced
from £32,475. The UK’s
top-spec V6 Stinger is the
similarly named but
different GT S.
US-only Stinger GTS: 800 will be made, all painted orange
H a b a N i r o’s sta n ce i s m a d e p ossi b l e by a n ew e l e c t r i c c a r p l atfo r m
Interior has plenty
of show car flourish
and futuristic tech