Drum brakes are an OG technology that has been around almost as long as cars. First developed in 1899, this style of brake was found on some of the very first prototype automobiles built by Wilhelm Maybach and Louis Renault. Barely younger than their disc-type alternative, drum brakes have long been the standard way to slow a vehicle down given their decent performance and inexpensive production cost. But they began to fall out of favor with automakers in the mid-1960s, when shorter-stop disc brake systems became widespread. Drum brakes are about to make a resurgence thanks to the growing popularity of electric vehicles.
Drums and discs work very differently and each system has its own advantages. Disc brakes work the same way as those on your bike: a pair of brake pads attached to a caliper dig into the rim to generate friction and slow the wheel’s rotation. In the case of automotive brakes, this is a dedicated metal plate (hence a disc) rather than the rim itself. Disc systems are more powerful and faster than drums, which is very necessary as the front brakes will support 60-80% of the momentum of a slowing vehicle relative to the rear, that is. why you will be hard pressed to find a car with front drums anymore. The discs are also self-adjusting, which means less gripping or pulling, and self-cleaning, which makes them quieter. They are also less prone to warping from prolonged heat exposure and won’t fade in hard braking situations like long descents.
Drums, on the other hand, have their brake shoes located in a cylindrical box that spins with the rest of the wheel and use a piston to press the two jaws outward, wedging them against the inner wall of the drum to create friction that slows down the vehicle. Because the inside of the cylinder has more area, the drum pads can be much larger than the pads on a disc, making them last longer and exerting a greater stopping force than pads on Similar sized disc calipers. Plus, since the drums are placed further into the wheel, they can easily serve as a parking or emergency brake, while vehicles with four-wheel rotors require the addition of a self-contained electric brake.
On the latest generation of electric vehicles, drum brakes actually make sense. Take VW new ID.4 and only in Europe ID.3 Electric vehicles, for example. Both models use Continental designed drum brakes on their rear wheels. “By design, drum brakes have no residual drag,” a spokesperson for VW’s North American region EV test team told Engadget. “The shoes are always opened by the internal springs. It helps to vary.
A VE regenerative braking system, which shifts the rear motor into reverse (turning it into an electric generator to recharge the vehicle’s batteries) each time you release the throttle, also functionally harmonizes with the drum brakes. With an electric motor sitting on the rear axle and automatically slowing it down during the regenerative braking process, the rear brakes won’t be used often, according to VW. You then run the risk of the discs rusting or corroding when you need them most if they are discs. Drums are generally immune to this problem because they are effectively isolated from the surrounding road environment.
A spokesperson for Volkswagen AG’s brake development department confirmed that “drum brakes look dated, but for an electric vehicle like the ID.4, it’s the perfect solution.” They highlighted the drums’ lack of residual torque and drag, as well as their lower wear and corrosion rates that result in lower brake dust emission than the discs, as the main benefits of the brake system.
“The drum brake, as integrated in the ID.3, offers many advantages, especially in the field of electric vehicles,” said Dr Bernhard Klumpp, Head of the Braking Systems business unit. hydraulic at Continental. a press release 2020, “for example a longer service interval of up to 150,000 kilometers.” This is effectively the lifespan of the vehicle.
In electric vehicles, where batteries can weigh as much as a U-Haul trailer, every gram is precious and every ounce has a cost. While disc systems can be more efficient than drums, they’re also much more mechanically complicated – and those extra components, like the self-contained electric brake, all add to the vehicle’s overall curb weight and sticker price.
And even though drum brakes have been around since the 19th century, the technology itself continues to evolve. Variants of the Continental brake system used in the ID.4, for example, are already in use in half a dozen other applications for various OEMs.
“We first started the development [of this brake system], to include the electronic parking brake… ”, Alejandro Abreu Gonzalez, engineering director of Continental’s hydraulic braking systems division, told Engadget. “We have another step forward which will be fully electromechanical for the drum brake, we continue to invest in this technology. “
Continental previously worked on the development of an all-in-one disc brake system in 2017 for the electric vehicle market, dubbed the New wheel concept. “The rim of the wheel consists of two aluminum parts, the inner aluminum load-bearing star with the aluminum brake disc and the outer aluminum rim well with the tire,” the company explained in a press release to the time. “Unlike conventional wheel brakes, the New Wheel Concept brake engages the aluminum disc from the inside. This allows it to have a particularly large diameter, which benefits braking performance.
Although the new wheel was never put into production, the work “certainly gave us a lot of information about new materials to reduce weight,” Gonzalez noted. “This is something that with heavy batteries we will definitely have to continue to develop.”
Gonzalez concedes that changing the public’s perception of drum brake technology as archaic and inferior to discs remains a challenge. But while we’ll probably never see a comeback of four-wheel drum systems, especially not in high-performance and sporty vehicles, “For city driving, I think that’s the best technology that makes sense here for electric vehicles. “
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