Whatever the architecture of future brake systems will look like – every car will continue to need wheel brakes

The need for deceleration, emergency stopping, stabilization, standstill management and fail-safe operation makes wheel brakes indispensable. However, on top of that, brakes have to contribute to lower CO2 and dust emissions.

Electrification will also bring a revival of the drum brake. Brake calipers, on the other hand, will similarly be optimized for the specific boundary conditions of electrification and for specific types of vehicles. The braking hardware is as much on the move as software and architecture are.


Calipers – Powerful. Green. Sustainable

Calipers are still an attractive choice, particularly on the front axle (FA) and for vehicles with a greater mass. As discs with calipers dissipate heat very well owed to their open design, they are perfectly suited for delivering very high braking power to decelerate a vehicle with a lot of kinetic energy. This is reflected in Continental’s expertise in developing calipers for hard-coated discs, which reduce particle emissions from this brake type.
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Dust generated through braking (disc/drum and brake pad/shoe abrasion), however, is another challenge for the automotive industry. The future aim is to reduce the particulate matter (PM) emission of this type of dust in order to lower the overall vehicle particle emissions. For calipers, one of the current approaches is to apply a hard coating to the brake disc, which reduces abrasion. However, this solution is cost-intensive as the coating is expensive.

To also reduce the residual friction of the brake shoes, which remain in contact to the disc after the braking action, a caliper design with a greater air gap between disc and pad is available, as well as a solution for active brake pad retraction.

Downsizing of Calipers – Less weight. Greater efficiency

Downsizing is another innovation path that Continental is pursuing with calipers. The potential for further downsizing is a result of electrification: In an electric vehicle equipped with a brake-by-wire system such as the MK C2, up to 80 percent of all deceleration events can be covered with regenerative braking during a normal driving style. Assuming that braking actions are consistently started with regenerative braking, this percentage can go up as high as 95 percent.
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In other words, in an electric vehicle with an optimized regenerative braking strategy, the wheel brakes are hardly ever used for deceleration. This change can be utilized to downsize the calipers, which saves wheel-sprung mass and contributes to vehicle efficiency. As infrequent use of a caliper can potentially cause issues due to brake disc corrosion and less aggressive brake pad surfaces, Continental is also working on solutions for keeping a caliper fully operational despite longer downtimes.

Drum Brakes – No corrosion. No residual drag. Ideal for Electric Vehicles

With the EPB-Si, Continental is manufacturing and supplying a patented drum brake solution that fits the bill of sustainability and green braking especially well. It eliminates corrosion, reduces brake dust – and the electric parking brake functions are also integrated into the patented design.
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Once the wheel brake is no longer the workhorse of deceleration, it turns into a “fallback system” that is only needed in exceptional situations. When this happens, drum brakes can play to one of their particular strengths: As the drum brake is a system fully enclosed by a housing, the mechanics and brake surfaces inside are well protected against ambient influences such as rain and salt, which cause corrosion. As the brake shoes are also retracted from the drum surface by the force of a spring, residual drag is not an issue with the drum brake.

Yet, the drum brake has another trump card to offer: It causes hardly any particle emissions. Thanks to the closed design, brake dust accumulates within the brake and can be collected in a reservoir at the bottom of the brake drum. During brake service this reservoir is emptied by suction-cleaning. This level of brake dust reduction is hard to achieve with a caliper.

Considering this mix of system properties, the drum brake is an attractive choice, at least for the rear axle of electric vehicles. Depending on the vehicle segment, it is also an attractive option for the front axle of vehicles with a lower mass.

Dry Drum Brakes – Smart. Dry. Sustainable

In this completely new type of duo-servo brake, sensors measure the effective brake moment, and the system’s high control rate ensures that exactly the requested force is applied by the compact electric actuator and gear unit inside the dry drum brakes – the braking force is thus perfectly balanced at both wheels. So electrification may well result in a comeback of the drum brake and is also likely to trigger the next step to dry braking.

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As the electrification of vehicles is making rapid progress, the mechanical part of brake actuation – the hydraulics – can be replaced with an electric actuation. The first solutions for “dry” braking are likely to be installed on the rear axle – where the drum brake is naturally at home.

In fact, the drum brake is well suited to this approach because it offers a design advantage for electrification: Owed to their principle of operation, drum brakes require less actuation power, which results in small and light motor-gear-units inside the brake. The drum’s rotation causes a self-enhancement effect by pressing the two linings against the drum.

Drum brakes with electromechanical actuation are therefore a particularly good match for efficient electrified mobility. Continental is addressing this requirement with developing the lightweight e-DS, a dry drum brake without hydraulics.

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