Automotive Engineering - April 2022 - 14

Airing on the side of
COVER STORY
INNOVATION
Lucid lighting experts
engineered the Air's
LED-based headlamp
modules that use a
microlens array optical
system featuring
switchable light
channels and a solidstate
high beam linked
to the car's steering.
Each microlens has a
direction and a focal
length. Miniaturization
of the modules
enabled designers to
give Air the industry's
slimmest lighting
apertures.
Inside the unique drive module
Among the Air's tech stars, the drive module may shine brightest. It's a
triumph of systems engineering and thorough analysis of electromagnetics,
motor topology, power flow and cooling. According to Bach, the
geometry and physics that went into the design are what give Lucid's
motor its formidable power density. The drive unit can be used for the
front, rear, or on both axles in the vehicle; only the motor mounts are
different. In the Air, the rear drive unit is rotated 90 degrees to make it
" flatter " in profile and thus provide more luggage-compartment volume.
The electric machine is an oil-cooled permanent-magnet design,
optimized to reduce internal resistance to free spinning, Bach said.
Uniquely, the differential is located inside the rotor, " our secret
sauce, " he calls it. Rawlinson describes the arrangement as " a single
rotational inertia system " that avoids the tolerance-related losses
inherent with many motor-gearbox pairings. The design engineering
is most remarkable when viewed in a cutaway display motor at Lucid
HQ (unfortunately, photos were forbidden during our visit). The engineers
said they looked forward to teardown specialists Munro &
Assoc. fully dissecting an Air and reporting their findings.
While brainstorming the motor concept in the context of power density
and miniaturization, the team discussed how to utilize the space
within the center of the rotor. " We realized that it was the most logical
space for the differential, " Bach recalled, " because the center of the
rotor doesn't generate torque; it's typically dead mass within the lamination
stack. " They decided to sequester that space and engineer a
small, lightweight, high-speed/low-torque differential to reside there.
With the diff inside, two planetary gearsets (one each for left and right
differential speed) were engineered into the transmission design.
The planetaries and their tooth profiles also were designed inhouse
to meet the team's stringent spec for " perfect gear meshing
under high- and low-load conditions, " Bach explained. Again, every
percent of efficiency gained is important. The gearing is oil-lubricated
via a small pump that delivers oil from a compact sump,
through an annulus to cool the stator and end windings. It also lubricates
the differential.
14 April 2022
Drive module with integrated inverter at top, installed in the Air sedan.
" It's all optimized for efficiency. You can't achieve
the efficiency we wanted in this system by going to an
outside supplier, " he said. The heat exchanger mounts
directly on the electric machine; pressurized coolant
flows in to cool the inverter in situ, transferring the
heat into the oil which then cools the drive unit. A look
inside the cutaway property reveals the resolver, also
an in-house development. Integrated with the rotor
shaft, the resolver determines the clocking angle of
the rotor. " A motor supplier would not have come up
with the idea of integrating the resolver and rotor
shaft, " Bach asserted.
AUTOMOTIVE ENGINEERING
FROM TOP: LUCID MOTORS; LINDSAY BROOKE
Automotive Engineering - April 2022

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