72 TheEconomistJuly 13th 2019
1A
t the dawnof the motor industry one
of its pioneers, Ferdinand Porsche,
caused a sensation at the Paris World Fair
in 1900 with a vehicle driven by a pair of
electric motors incorporated into its front
wheels. This arrangement allowed the
Lohner-Porsche (pictured above) to dis-
pense with cumbersome belts, chains and
gears. It was thus able to nip along at a
heady 35kph for up to 50km after its lead-
acid batteries had been charged up.
Porsche, like other carmakers of the
time, eventually turned to the internal-
combustion engine for greater range and
flexibility. His eponymous firm went on to
build some of the fastest sports cars
around. But despite the fact that electric ve-
hicles are now returning to the road with a
vengeance, the idea of using “in-wheel”
motors of the sort Porsche pioneered has
failed to follow suit. Some vehicle manu-
facturers and their suppliers, including
Michelin, a French tyremaker, and nsk, a
Japanese component-producer, have de-
veloped modern versions of in-wheel
drives for cars, but these have yet to make it
into production models.
There are two reasons for this reluc-
tance. One is that an in-wheel motor’s com-
ponents and wiring are exposed to the ele-ments rather than being snug inside a
vehicle’s body. They must therefore be ro-
bust enough to handle the high voltages
such motors normally require while simul-
taneously being protected against damage
from road debris and the risk of shorting
out when periodically soaked in water. The
other concern is that the additional weight
of the motors on each wheel increases a ve-
hicle’s “unsprung” weight—the part of its
mass not supported by its suspension. A
high unsprung weight results in a bumpy
ride and poor handling.Taking a load off
All this means that most electric cars con-
tinue to use drivetrains that resemble
those found in combustion-engined vehi-
cles. They have an electric motor at the
front or the rear (or, sometimes, both)
which turns the wheels via shafts and
gears. But if Indigo Technologies of Cam-
bridge, Massachusetts has its way, all this
will change. Since the firm was founded in
2010 by Ian Hunter, a professor of mechani-
cal engineering at the Massachusetts Insti-
tute of Technology, Indigo’s engineers have
been developing an in-wheel drive system
they call the t1. They believe that their sys-
tem, a module that incorporates brakes,steering and an active suspension, as well
as a motor, overcomes both the electrical
problem and the unsprung-weight pro-
blem, thus paving the way for in-wheel
drives to become mainstream.
To reduce the electrical difficulties, the
t1 runs at 48 volts instead of the 400 volts or
more used by the motors in existing elec-
tric cars. The choice of 48 volts is not arbi-
trary. That voltage is also rapidly becoming
standard for the circuits which run things
like lighting, climate control, entertain-
ment systems and adjustable seats, even in
conventional combustion-engine-driven
cars. Lowering the voltage almost tenfold
in this way does, though, make the t1’s mo-
tor easier to protect and insulate, which in
turn makes it cheaper to produce than
higher-voltage motors, says Brian He-
mond, Indigo’s boss.
All this is possible because fitting t1s to
all four wheels eliminates the need for
driveshafts, transmissions, suspension
parts and other weighty components.
Those weight savings allow the size of the
battery pack to be reduced, saving still
more weight.
Reduced vehicle weight means also that
the propulsive motors do not need to be as
powerful as those of conventional electric
cars—especially as the task of propulsion is
divided four ways between them. Nor are
any gears involved, for the motors turn
only as fast as the vehicle’s wheels, which is
a relatively low speed for an electric motor
and further reduces its need to be power-
ful. That translates to a low voltage because
the power of such a motor is a product of
voltage and current (P=V*I, one of the fun-
damental equations in electricity). At aAutomotive engineeringBack to the future
Putting a car’s propulsive systems directly into its wheels is a century-old idea
whose time may at last have comeScience & technology
73 Searchingfora newredpigment
73 TheancientestGreek
74 Penguins and tourismAlso in this section