Automotive Engineering - March 2025 - 21

TECHNOLOGY REPORT
COMPONENTS
Mercedes proposes 'in-drive brakes' for better EVs
From humble Chevrolet Bolts to sixfigure
Lucid Airs, every EV can reverse
its electric motors to slow the vehicle
while harvesting energy for the battery,
the efficient tag-team process known as
regenerative braking.
Today's EVs do this so well that traditional
friction brakes, which clamp onto
a spinning wheel rotor or drum, can
seem an afterthought. Witness
Volkswagen's decision to equip its ID.4
with old-fashioned rear drum brakes,
with VW claiming drums reduce EV rolling
resistance and offer superior performance
after long periods of disuse.
At Mercedes-Benz, engineers say
their regenerative brakes already slow
the company's EVs on their own in 98%
of driving situations. Its upcoming CLA
electric sedan - a critical model in the
wake of the EQS sedan's sales flop -
can generate up to 200 kW under braking.
With friction Mercedes' solution is
called " in-drive brakes, " which it
showed off recently at its R&D center in
Sindelfingen, Germany.
These innovative stoppers are integrated
directly in electric drive units,
sharing space with a motor, transmission
and differential. The system switches up
the usual role of brake pads and a spinning
rotor. A pair of stationary brake
discs, to the left and right of the motor/
transmission unit, squeeze against a
Mercedes-Benz displays its
in-drive brake at its Innovations
& Future Technologies
2024 event.
spinning, two-sided circular brake pad
that's connected to the driveshaft.
Mercedes cites several advantages.
The system would divert about 200 lbs
(91 kg) of unsprung mass from a car's
corners to the inboard side of its suspension.
That would improve wheel
control and ride quality.
Mercedes claims squeaky discs and
other brake noise would be eliminated,
with reduced wear and virtually no
maintenance. With no need for outboard
brake cooling, designers could
improve aerodynamics with fully enclosed
wheel designs, in any imaginable
style. (Though something tells us that
fake five-spoke classics would quickly
Mercedes says its
new in-drive brake
technology produces
no emissions from
brake dust and
eliminates brake noise.
join today's pretend EV grilles.)
With the brakes moved to an aluminum
housing, drivers could say goodbye to
unsightly brake dust on those precious
alloy wheels, and their associated emissions.
A pan below the motor housing
captures that nasty particulate for the life
of the vehicle, again with no maintenance.
As for two-wheel-drive EVs, the all-in-one
drive units can pair with conventional
brakes on the non-driven wheels.
Cooling the system remains a key
engineering challenge. Even if regen
handles 98% of stops, the other two
percent - think hard stops in heavy
traffic - can generate copious heat,
above 300°F (149°C). Mercedes can run
coolant through the motor unit's brake
discs. Ideally, the brakes would be
plumbed into the same cooling circuit
that soothes the motor and battery.
Therein lies the problem: With a lithium-ion
battery preferring a comfy 6085°F
(16-29°C), and spinning electric
motors running at 180°F (82°C), putting
friction brakes on the same cooling circuit
could push the battery and motor
beyond optimal temperatures.
Mercedes is working in its labs to overcome
that issue, and has yet to test the
system in roadgoing prototypes.
Add it to Mercedes' to-do list, along
with fixing the jellybean blahs of its EQbranded
sedans.
Lawrence Ulrich
AUTOMOTIVE ENGINEERING
March 2025 21
BOTH IMAGES: MERCEDES-BENZ
Automotive Engineering - March 2025

Table of Contents for the Digital Edition of Automotive Engineering - March 2025
