Over the past few decades, electrification has resulted in the virtual elimination of several once-key automotive liquids. Power steering fluid is the most obvious example across the board, but electric vehicles have also dispatched with engine oil, automatic transmission fluid, and of course, gasoline. However, innovators in the industry aren’t done yet. Two suppliers have already developed solutions for eliminating another common maintenance fluid: brake fluid.
While there are already cars available with brake-by-wire pedals that actuate the brake master cylinder electronically, Brembo’s Sensify and ZF’s EMB take things one step further and feature electrically actuated calipers rather than hydraulically actuated ones. In the case of the former, all four calipers can be specified to feature an electromechanical mechanism that clamps the pads to the discs, while in the case of the latter, all four calipers or only the rear calipers can be electromechanical, with the second setup controlling each hydraulic front caliper by way of a separate electronically actuated master cylinder. Contrast this with a traditional brake caliper setup in which all caliper pistons are acted upon hydraulically, and it’s clear we’re soon to be playing in a whole other realm.
So what benefits do electromechanical brakes have in the real world? Well, they promise faster actuation than hydraulic brake solenoids, which should lead to more precise control of each individual wheel. Automatic adjustments can be made at the calipers themselves for weight transfer and differences in surface friction, and threshold braking in seriously slippery conditions can be achieved by computer algorithms rather than by driver skill. Also, since the pedal is entirely electronic, there’s no heavy traditional pulsating anti-lock braking feedback that may scare drivers not used to getting into ABS during panic braking instances. In addition, electromechanical calipers promise to eliminate brake pad drag which should reduce particulate emissions, and they should integrate seamlessly with regenerative braking in electrified vehicles.
There are purported perks for automatic emergency braking, too. ZF claims that its electromechanical calipers can offer a 29.5 feet reduction in automatic emergency braking stopping distance from 62 mph over a standard hydraulic braking system. That could be the difference between changing your shorts and filing a claim, but without further details on how that number was reached, we’ll have to wait on third-party validation.
Oh, and there are some potential maintenance benefits to this evolution of brake-by-wire. Because electric calipers keep the pads clear of the discs in regular operation, it’s possible that pad changes could be a cinch. There might not be a need to retract the pistons if retraction is their default state to avoid dragging the pads on the discs. Also, removing the need for traditional brake lines eliminates the possibility of having, say, a rear brake line rot out after 20 years in the rust belt. It also means that brake fluid flushes on electromechanical calipers literally can’t be neglected (because there’s no brake fluid to flush).
Are there any potential downsides? Well, I could see a few. The first is unsprung weight, as adding a powerful electric motor and mechanism to a caliper is almost certainly a heavier proposition than a few ounces of flexible brake tubing and brake fluid. The second is packaging, because oh brother, these calipers look huge. Sure, they mean manufacturers won’t have to run brake lines, but the sheer depth of the calipers may require compromises in knuckle design and suspension arm placement to achieve sufficient steering angle. I also can’t help but wonder about rats. They don’t normally chew metal brake lines, but wiring? Happens all the time.
Still, so long as rodents don’t find themselves attracted to the cabling, electromechanical brake calipers offer up some interesting possibilities. With contracts already inked as per Automotive News, expect to see these systems appearing in production cars within the next few years.
Top graphic images: ZF
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Considering how numb and disconnected Toyota brake have been since (checks watch) “forever”, I’m sure they are eager to adopt this system and remove any last possibility of authentic driver feedback.
When the weather is nice I drive an old school vehicle; no ABS, no traction control, mechanical steering with power assist, and boosted brakes. Not 100% free from aids, but not far off. It’s a very analog experience and you can feel absolutely everything the vehicle is doing.
I’d be very hesitant to move to a full electric braking system. One computer error, a degraded caliper piston position sensor signal, or just a loss of power means no braking. At least with a hydraulic system I can engage leg-day and get to a controlled stop. Some systems should just always have mechanical redundancy.
As soon as brake by wire was the move, electric calipers became the obvious answer. The advantage of fluid is that it transfers pressure feedback right to the pedal, as soon as you’ve added one electromechanical actuator, having 4 only makes it safer. Not only do you get all the performance benefits of individual wheel braking and millisecond-precise antilock systems, you also get the benefit of redundancy. A failed actuator would leave you with 3 wheels still working just fine, and multi-piston calipers would mean any one failed actuator only decreases braking efficiency on that wheel, which the system could detect and compensate for.
2 concerns are that it’d eat up battery range on EV’s (at least when going for a spirited drive), mitigated by the fact they’d probably stay off most of the time due to regen, and the possibility of a dead control module bricking one’s brakes, which sounds pretty spooky to me.
It’s really exciting as an engineer. As a driver, I like hydraulic feedback and manually threshold braking.
Will BMW make you subscribe?
Hydraulic brakes still work if the car’s entire electrical system fails. These, not so much. I guess you could use capacitors or something to create redundancy, but this seems like a solution to a problem that doesn’t exist.
Meh, if you lose electrical power you can lean on the electric emergency brake
Currently sporting electric brakes since sometime in 2009, for many of the same reasons listed above: the Boeing 787.
They should make “brake by magnets.”
That would piss the Turd off bigly.
That’s regenerative braking.
I wonder how the brakes would handle something like track use under very high temperatures, and if the brake pedal itself will provide any feedback
Oh goody, more unintended corrosion possibilities!
I’m a little leery of any kind of braking system innovations, given that I work at a BMW dealership and see non-stop recalls for the integrated braking system control module. Somehow I feel like adding even more electronics to the mix isn’t a great idea.
I’ve never had a hydraulic system actually fail to stop a vehicle. I’ve had leaks that needed to be fixed, boosters that have died, but never had a vehicle with total brake failure. If every computer, chip, sensor, and wire on my vehicle were to suddenly fry all at once, I can still steer and stop.
As long as my iPhone flushes my toilet.
I’ve been to Japan recently, and their toilets are more advanced than their phones. It is a bit strange in that regard.
Japan has been in the Year 2000 since 1970
Just keep a cable going to at least one or two of the rears for backup and I’m not entirely opposed. And make sure the pedal feel isn’t absolute shit. Hydraulic brakes are a failure prone pain in my goddamn ass, if executed properly, this would be great. Still a hard no from me on steer by wire though.
But we already gave up manual cable parking brakes years ago, so I would not count on any system with full electric braking to include a manual cable and drums inside the rotors when “a few lines of code and a cheap button will do that just as well for $150 less per vehicle.”
Personally I am not comfortable trusting my life to electronic braking. Seeing weird electrical stuff happen in multiple modern cars and still remembering that the Hummer EV had malfunctioning brake lights which at this point we as a species should have NAILED DOWN leads me to not want to take that gamble. Bare legal minimum should be a real handbrake physically connected to the brakes if all else is electric.
Yeah, if a nuke goes of the EMP will bork the brakes.
I’m pretty sure the electric power steering in my vehicles is a self contained electric powered hydraulic pump mounted on the steering rack. So no changeable fluid, but it’s still there.
The assembly plant folks will like this a lot eliminating fluid additions on the line.
We got some bon bons when we started providing pre-filled automatic transmissions.
Power steering conversion to electric was similar.