Automotive

Mercedes reinvents the brakes for electric vehicles

Mercedes reinvents the brakes for electric vehicles
Mercedes-Benz in-drive brake system for EV cars
Mercedes-Benz in-drive brake system for EV cars
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The in-drive brake pads resemble friction pads inside a clutch
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In-drive brake
Mercedes-Benz in-drive brake system for EV cars
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Mercedes-Benz in-drive brake system for EV cars
Exploded view of the in-drive brake system that fits inside the Mercedes-Benz EV drivetrain
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Exploded view of the in-drive brake system that fits inside the Mercedes-Benz EV drivetrain
The Mercedes-Benz in-drive brake system fits inside the electric motor drivetrain pictured on the right
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The Mercedes-Benz in-drive brake system fits inside the electric motor drivetrain pictured on the right
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In the simplest terms, nearly every modern car on the planet uses disk brakes: a rotor attached to a hub with a caliper with brake pads fixed to the control arm at each wheel. The driver presses the brake pedal and hydraulic fluid is pushed down the brake lines into the caliper, expanding the pistons and pushing the brake pads against the rotor, slowing down the rotation of the rotor connected to the hub, thus slowing down the wheel.

There are other systems, like drum brakes, air brakes, band brakes, the Flintstones method, et cetera, that have also been around since the dawn of the automotive industry. The concept almost always remains the same: using friction to slow down. And so it doesn't go unsaid, yes, there are compression brake systems as well, but that's entirely different.

Mercedes-Benz has put a new spin on an age-old concept with what it calls "in-drive brakes" for electric vehicles. The system being developed at the company's research and development department in Sindelfingen, Germany, integrates the brakes right into the drivetrain, in an arrangement that works very much like a transmission brake. It resembles clutch plates – but with a unique twist.

The in-drive brake pads resemble friction pads inside a clutch
In-drive brake

There are no calipers, instead a circular brake pad connected directly to the output shaft of the electric motor is pressed against a stationary water-cooled ring, all of which is in an enclosed system.

According to Mercedes, the in-drive brake system shouldn't require servicing for the life of the vehicle, potentially saving the owner thousands of dollars in brake repairs and replacements. Even the brake dust is collected in a small inner compartment that won't require emptying.

Brake dust is a major contributor to pollution, particularly in urban areas with lots of stop-and-go traffic. And if you've ever driven down a long, steep grade like the Grapevine, just north of Los Angeles, California, you're no stranger to the smell of brake dust – and the discomfort in your nasal passages. EV motors inherently act as a brake when the accelerator is released, as EV motors have the ability to regenerate electricity back into the batteries, slowing the vehicle down in the process. An actual brake system is still needed, however.

Though the in-drive brake is still undergoing testing, Mercedes reckons that brake fade will be a non-issue as the system is water-cooled. Given the in-drive brake system relocates all the necessary "slow down" bits away from the wheels, unsprung weight (weight that isn't carried by the chassis, and instead spins or moves with the wheels, creating gyroscopic forces) is significantly reduced, making the vehicle both handle better and improve the ride. Wheels could also be made more aerodynamically efficient without the constraints of rotors and calipers.

The Mercedes-Benz in-drive brake system fits inside the electric motor drivetrain pictured on the right
The Mercedes-Benz in-drive brake system fits inside the electric motor drivetrain pictured on the right

The biggest upside to in-drive brakes? No more looking at rusty rotors on your otherwise beautifully pristine US$180,000 Mercedes-Maybach EQS 680 SUV. Tongue-in-cheek, of course. A brake system that doesn't require repairs will save owners downtime and money. Consolidating components also saves the manufacturers money and necessary materials, making a smaller impact on the planet.

And with Euro 7 emissions standards starting in 2026, the dust-sealing design will be ahead of the curve.

While Mercedes focuses on reimagining traditional brake systems for its electric cars, other companies are rethinking the entire architecture of electric vehicles. REE has taken an interesting approach by relocating everything "under the hood" into the wheel wells. Motors, drivetrain, steering, suspension, and brakes are all located in the wheel wells, creating a modular platform – one that very much resembles a skateboard – on which anything can be built on top of, from delivery trucks to sports cars to camper vans.

Whether Mercedes' in-drive brakes become a new standard or ends up as a premium upgrade for affluent EV buyers, only time will tell.

Source: Inside EVs

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16 comments
16 comments
paul314
If your drivetrain is electric, the right combination of electric/magnetic fields should be able to do your braking for you without involving mechanical friction and a bunch of heat. Yes, as you slow down, regenerative braking becomes less efficient, but with fancy enough circuit design and sensors you can expend some current to finish the stopping process. (Keeping the wheels locked by electricity alone might be an H-bridge too far, though, so you might still need a mechanical component in there.)
vince
With an AWD electric car you could do it one better and have the rear drive disconnect from motion and reverse and try to spin wheels backwards but without slipping using ABS technologies. With good engineering it might be possible to actually "stop on a dime". Of course this woukdnt work with front brakes as you could easily spin car around pkus massive inertia pushing down on front wheels would be hard to control if thwvtires truws to rotate backwards.
Chase
@paul314, regen only works if you have the battery capacity to take that energy, which means the maximum effect is reduced the closer you are to 100% capacity, and is worthless if you happen to live on a hill and fully charge your EV overnight (arguments for not fully charging your EV can certainly be made, but most people don't want to spare the cognitive cycles to understand why).

On to my concerns:
As far as I can tell, there is no way to bias this system to apply breaking power to one wheel over another, nor any way to release it from one while but not another. So ABS and brake-vectoring would appear to be out the window. Also, this would require a dual-motor (at least) setup so that you can have brakes at both the front and rear, or you'd need traditional brakes at the rear in a single-motor configuration.

Seems the simpler solution to unsightly rusted brake rotors and annoying unsprung weight is to just move the traditional brake rotors and calipers inboard, next to the motors/differentials. The only vehicle I know of, off the top of my head, that does this is the HMWVV/H1 Hummer. It's a weird design, but it does have its benefits. Probably the only good part of that vehicle's design though. That thing is/was hot garbage.
hemachayart
They still not using EDDY Current Break System
-dphiBbydt
My 1979 AlfaSud Sprint had inboard disc brakes - liquid cooled, but only when it was raining.
dhdallas
But what about my showy big red calipers? Oh, the horror!
Erik
Define "for the life of the vehicle" they said the same about sealed automatic gearboxes, but the manufacturer has a 10 year lifetime or shorter or maybe 180000 km, after that they think it's eol. Surprise surprise cars aren't written of in the real world that fast so the second or third owner has no doubt very expensive brake repairs in the future.

Which means second hand prices plummet, so the first owner writes off a huge amount, which makes it very expensive brakes you "don't have to service".

What was the benefit exactly?

Rick O
Not sure how they'll handle ABS systems. And a "lifetime brake" just means you have to replace a lot more than just the brakes when something goes wrong. Also, you'll be doing all your braking through the CV axles, which will inevitably lead to more axle replacements.
McDesign
Break a half-shaft; lose that brake - hmmmmmm.
TechGazer
For wheels driven directly from motors, it doesn't really apply. For more complicated drivetrains (gears, yokes), you may have trouble from stresses applied further from the wheel. There's probably not much experience with those stresses applied to those components, so unexpected problems are likely, leading to recalls and/or expensive repairs.

Isn't brake maintenance fairly cheap? When my disk brakes start dragging, I simply take them apart and clean&grease the pistons or replace the o-rings. Cheap and easy. I've also replaced the calipers, which cost well < $100. Drum brakes are cheap and easy too. I have no idea what brake shops charge, but it _should_ be really cheap in terms of parts and time. I think it's unlikely that an untried design will end up providing much savings in overall cost of ownership.
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