Automotive Engineering - August 2021 - 18

Making the case for
IN-WHEEL
MOTORS
The number of IWM developers and their technology solutions in the global mobility industry is expanding.
case, differential, rear axle, half shafts) can exceed 250 kg (551 lb.)
the resulting mass balance can be favorable for IWM versus alternative
e-AWD configurations.
The mass comparison becomes even more favorable for IWMs if
their higher efficiency is considered. By eliminating the transmission,
a direct-drive IWM can be a few percent more efficient under typical
driving conditions. This can translate either into longer range or using
a ~20 kg (~44 lb.) lighter battery for the same range. For low-speed
urban vehicles, high IWM efficiency and distributed power at each
corner could lead to a lighter, air-cooling solution.
Similar analysis needs to happen for cost at the vehicle level. Although
four IWMs and associated power electronics will cost more than one- or
two-motor solutions, at the vehicle level, the overall cost equation can
be favorable for IWMs if elimination of drivetrain components and reduced
battery energy requirements are considered.
For the customer, more obvious benefits of IWM may be in vehicle
dynamics performance and vehicle design features. Compared
with the 200-300ms needed for spooling up air intake, engine and
driveline components, IWM can apply torque near-instantaneously
and more precisely so that there is less pitch during braking and
less roll when cornering. Eliminating the front center-mounted traction
motor can provide a larger " frunk " (front trunk). Eliminating
the rear axle offers the potential to lower the pickup bed or SUV
trunk floor for easier loading/unloading; a loading area comprising
the entire length of the vehicle also is possible. The absence of incompressible
motor hardware in the load path can be exploited to
manage impact forces into the structure and potentially improve
passive safety.
18 July/August 2021
Several future mobility trends are favorable to
IWMs. Increased fleet ownership for shared vehicles
and goods delivery will drive decisions based on lifecycle
costs; elimination of gearboxes and driveshafts
could improve reliability for IWM-driven vehicles.
Urban mobility, where a greater portion of the world's
vehicle-miles traveled (VMT) are generated, will place
more importance on vehicle compactness: IWMs can
enable shorter vehicles that still offer the same occupant
and battery storage space. They can also enable
relevant urban performance, even offering 90-degree
articulation, to greatly enhance parkability.
For robotaxi operators that need to maintain and
store vehicles overnight, enhanced parkability converts
into lower real estate costs (often in expensive cities),
as well as faster passenger pickup and drop-off times,
leading to more paid rides per day and increased profitability.
The smoother ride quality enabled by IWMs can
reduce the risk of motion sickness in autonomous vehicles
and risk of freight damage for delivery vehicles. A
lower load floor not only improves loading/unloading
but can improve entry/egress for an increasingly aging
population and for wheelchair users. Car-free centers,
being proposed by several European cities, could stimulate
new door systems, such as front entry with the requirement
for a low step-in height and floor.
IWMs are being developed by a variety of companies
(table above). The growing roster includes " pure
AUTOMOTIVE ENGINEERING
INDUSTRY SOURCES

Automotive Engineering - August 2021

Table of Contents for the Digital Edition of Automotive Engineering - August 2021