Picture the way brake dust turns your shiny silver wheels into a dull, gray mess. Now imagine what it does for your lungs.
When we talk about automotive emissions, we’re typically not thinking about brakes. The European Commission is, though, and in the Euro 7 standards set to come into effect next year, there are limits on particulate emissions from brakes.
According to a 2023 Automotive Engineering article, the limit for Euro 7’s introduction is set at 7 mg/kilometer, and in 2035, the limit will reduce to 3 mg/km. Euro 7 will allow electrified vehicles to have higher brake-emission levels, depending on the type of powertrain, operating under the assumption that motor-regenerative braking means less use of the friction brakes.
Regardless, there’s a real need to cut brake dust. Brembo’s approach is called Greentell, a portmanteau of "green" and "intelligent." Maybe not the most elegant name, but a neat piece of technology.
"When Euro 7 will be applied in Europe, the legislation will impact all passenger vehicles or most of them," says Fabiano Carminati, Brembo’s head of brake-disc development, in an interview with Motor1. "So this is the reason why we needed to find a solution from a technological point of view that can be useful for huge volumes, not just a few thousand pieces per year."
A generic example of Laser Metal Depositon.
That solution revolves around Laser Metal Deposition (LMD), a relatively new form of additive manufacturing where powdered metals are heated by a laser and sprayed on a metallic surface. Without getting too in the weeds, think of it as printing metal. Brembo uses LMD to coat the surface of its brake discs with a proprietary—secret—alloy. Carminati tells us Brembo applies this dual-layer coating after the machining process, and before the final finishing.
The results, according to Brembo, are fairly astonishing. On the Worldwide Harmonised Light Vehicles Test Procedure (WLTP) for braking, Brembo claims a 90-percent reduction in particle emissions from its Greentell system. Carminati also says the LMD process only adds minimal time to the manufacturing process.
Brembo also says that the LMD coating reduces disc surface wear by about 80 percent compared to an uncoated cast-iron disc. But Carminatti is quick to stress that this doesn’t translate directly into an 80-percent increase in disc life, because Greentell discs are actually thinner than traditional cast-iron units. He says Greentell discs should last about 20 to 30 percent longer than their cast-iron equivalents.
The new disc coating also required Brembo to develop a new pad material. “The coupling between the discs and pads is completely different than in a standard cast-iron material,” Carminatti says.
Also, because of the relative lack of surface wear, Brembo created a new indication marker for disc life—its logo, etched into the surface. Brembo can replace this with the logo of an automaker, too, but regardless, when the visible logo is gone, it’s time to replace your discs. A neat detail, which comes from racing. In the cast-iron brakes you see on GT cars, Brembo debosses its logo into the disc surface as a wear indicator.
Carminatti tells Motor1 that, beyond reducing emissions, the overall goal with Greentell wasn’t necessarily to improve braking performance, but to provide the same level of stopping power while ensuring consistency in all conditions. LMD provided the best solution without the risk of the coating becoming delaminated from the disc in cold and/or salty conditions.
Slotted and drilled rotors have long been associated with high-performance cars, but you won’t see a Greentell disc with such cuts or holes. Slotted and drilled rotors were originally designed to prevent “gassing-out,” a phenomenon where worn-off pad material creates a boundary layer between the pad and rotor surface, significantly reducing braking performance. But they create a more abrasive surface, which increases particle emissions from the disc. Which would negate the entire point of this exercise.
Not that you should worry about cooling or stopping power with these plain-surface discs. We’ve come a long way with material science since drilled and slotted discs first arrived, so gassing out isn’t really a concern these days. Holes and slots are mostly present these days for weight savings, cooling, or to get a bit more bite from the pads.
Since these brakes are designed to help automakers meet Euro 7 emissions, Brembo says it’s mainly targeting the European market, though they could come to the US eventually if an automaker wants them. (We don’t have any rules about particle emissions from brakes here, though we do have regulations on certain materials used in braking systems.) And Brembo being Brembo, Greentell is targeted mostly at premium and performance cars, its typical market. For aftermarket customers, Brembo also offers a similar product, Greenance, which targets similar emissions reductions.
This is, ultimately, a small piece of a very complex puzzle. Automakers and suppliers all have to be clever in how they meet the aggressive Euro 7 emissions, and it’ll take more than just electrifying powertrains.
