Mercedes Proposes “In-Drive Brakes” for Better EVs

March 1, 2025

Lawrence Ulrich

In-drive brakes will allow for closed wheel designs with better aerodynamics and higher efficiency. (Mercedes-Benz)

From humble Chevy Bolts to six-figure 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.

Mercedes-Benz’s in-drive brakes are integrated into the motor-transmission unit on the left and right and replace conventional brakes. (Mercedes-Benz)

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 brakes twiddling their metallic thumbs, the German automaker is questioning why they’re even taking up space within a car’s wheels.

Mercedes-Benz displays its in-drive brake at its Innovations & Future Technologies 2024 event. (Mercedes-Benz)

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 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 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.

Mercedes says it’s new in-drive brake technology produces no emissions from brake dust and eliminates brake noise. (Mercedes-Benz)

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 60-85 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 EQ-branded sedans.