The world's most efficient near-production electric car by Volkswagen uses AUMOVIO’s semi-dry brake system

With the MK C2 and the front axle calipers, AUMOVIO already supplies a braking system for the in-series ID. Polo that is designed entirely to support regenerative braking. As a so-called brake-by-wire solution, it transmits the braking command electronically and is therefore completely decoupled from the hydraulic system. Unlike electric brake boosters, which are still connected to the hydraulic system, this allows for regenerative braking without friction losses.

To ensure that as little kinetic energy as possible is “wasted”, the system decides on its own whether to engage the friction brake or whether the braking command should be used to recover energy via the electric generator. In the “Mission Efficiency” project vehicle, AUMOVIO has also optimized the hydraulic front axle caliper. Compared to the series model, this caliper can build up a larger air gap more quickly, thereby minimizing residual braking torque.

A new feature compared to the standard braking system on the ID. Polo are the electromechanical brakes on the rear axle. Instead of hydraulic pressure (“wet” brakes), the brake calipers are actuated by an electric motor (“dry” brakes) and therefore do not require hydraulic lines or brake fluid. Thanks to the faster electromechanical actuation, the air gap can be increased even further compared to the brake calipers on the front axle. This further reduces residual braking torque. Another advantage of the electromechanical solution is that the air gap can be actively adjusted via the electric motor, ensuring it remains constant. After the electric parking brake is applied or high braking forces are applied, the caliper is deliberately reopened, regardless of the previous application. Unlike with hydraulic brakes, there is therefore no memory effect – with an initially increased residual braking torque that would consume energy – even after heavy braking maneuvers.

Irrespective of the study’s focus, the semi-dry brake system offers further potential to make electric vehicles even more efficient and improve their performance. This primarily concerns driving dynamics because the EMB can distribute brake forces dynamically and individually to each wheel. This further improves regenerative braking performance, increases vehicle stability – especially when cornering – and enhances braking comfort. This effect can be further amplified in a fully dry system with electromechanical calipers on all four wheels.

To ensure situation-appropriate braking, the EMB can also intelligently adjust the air gap: When cornering, it increases the air gap to reduce residual braking torque; when hazardous situations are detected early, it reduces the distance between the brake pad and disc to bring the vehicle to a stop even more quickly.

Since the semi-dry system for the rear wheel brakes requires neither hydraulic lines nor brake fluid, weight can be reduced depending on the model; in addition, brake maintenance requirements are lowered. At the same time, design flexibility in vehicle architecture increases.

One example of an optimized hydraulic application is the “smart sizing” concept for brake calipers. To this end, AUMOVIO has specifically refined the brake design to meet the requirements of electric vehicles, streamlining and reducing the number of components. A smaller housing and an adjusted pad mass reduce the weight of the caliper. The concept also allows for a greater air gap, thereby reducing the residual braking torque. Since the brake engages further outward on a larger, thinner disc, less clamping force is required to achieve the same braking torque.

As part of the “Mission Efficiency” study, Volkswagen has unveiled the world’s most efficient electric car. With the help of new technologies (e.g. a solar roof) and adaptations to mass-production technology such as the MK C2, it recently set three world records that demonstrate its energy efficiency. First: It is more aerodynamic than any other car ever approved for road use. Second: During a so-called ideal drive (i.e. without inclines or auxiliary consumers), it achieved a record-breaking energy consumption of just 6.48 kWh/100 km. Third: Thanks to its aerodynamics and a highly efficient electric powertrain, the “Mission Efficiency” is also the most fuel-efficient near-production electric car. During a fuel-efficiency test drive from the Volkswagen Development Center in Wolfsburg, Germany, via Poznań (Poland) and Olomouc (Czech Republic) to the Austrian capital of Vienna, the “Mission Efficiency” electric motor achieved an actual energy consumption of just 7.51 kWh/100 km, including charging losses (6.89 kWh/100 km excluding charging losses).

Further information on “Mission Efficiency” is available in Volkswagen's press release.

_{[1] See the corresponding press release from Volkswagen: https://www.volkswagen-newsroom.com/en/press-releases/mission-efficiency-volkswagen-presents-the-worlds-most-efficient-near-production-electric-car-20691}