FRANKFURT, Germany – Drum brakes, an irrelevant passenger-vehicle technology except on limited small cars, are making a comeback for several reasons including the ability to help deal with particulate-matter emissions and corrosion.

This concept emerged during a recent The BRAKE Report (TBR) interview with two Continental engineers Sebastian Amrioui, Head of Advanced Products Hydraulic Brake Systems, and Dr. Mathias Haag, Technical Project Manager e-Caliper / Senior Expert Brake Function.

Continental, which engineered the drum-brake system for the Volkswagen ID.4 electric vehicle (EV) has been a leader in the resurrection of drum brakes.

In the first article from this interview, the Continental engineers explained how, thanks to regenerative braking, electric vehicles (EVs) no longer need the stopping power of an internal-combustion-engine (ICE) vehicle.

“The performance of a drum bake compared to a disc brake is lower, but now we have a situation that we need less performance because the brake does not work as much anymore because most of the deceleration is covered by the electric engine,” explained Amrioui.

Furthermore, he explained how one characteristic of drum brakes, being an encapsulated system, might be a detriment to braking performance when compared to disc brakes (by inhibiting brake cooling) but was a boon to controlling particulate emissions from deteriorating braking materials.

“The dust remains inside the drum,” Amrioui said. “With a disc brake, any particles go directly into the atmosphere. Small particles, smaller than 10 microns, can go right into the lungs and provoke cancer.

“And in the drum brake, an encapsuled system, a large part of the dust remains inside the drum and does not go into the atmosphere.”

There are methods of improving particulate emissions produced by disc brakes, but they present challenges.

“It’s possible to improve the system for particle emission for disc brakes and there are different technologies to do this,” said Haag. “On the one side, there is a large number of coatings for the discs and on the other end, there are filtration systems to catch the dust. But these are very, very expensive, adding additional measures within the vehicle.

“The drum itself has all the encapsulation features already installed, so there is a big advantage with the drum wherever a drum makes sense. And wherever customers are open for drum technology to improve particulate emissions and corrosion in the same application.”

The corrosion-fighting aspects of drum brakes also figured in Amrioui and Haag’s explanation of the positives associated with this technology.

“The encapsulation prevents water and salt going into inside the friction partners,” said Amrioui. “So, the drum brake has better corrosion behavior.”

The drum brake of the future will not, according to the Continental engineers, be your grandfather’s drum brake. It will most likely be made of composites (perhaps a front plate of aluminum and a friction ring of cast iron), weighing much less than previous iterations without any degradation of performance.

It might also be virtual lifetime product.

“We have done some endurance testing with the Volkswagen ID.3 EV (smaller EV than the ID.4) and there the lifetime of the drum brakes’ linings was greater than 300,000 kilometers (186,000 miles),” said Amrioui. “So, normally, maintenance is not needed on an electric vehicle’s drum brakes.”

There are further challenges – and opportunities – for the installation of drum brakes in a broader range of vehicles, a topic which will be explored in the next installment from this interview.