AUMOVIO has fitted Volkswagen’s “Mission Efficiency” concept car, which recorded real-world energy consumption of 12.1 kWh per 100 miles (7.51 kWh/100 km) on a drive from Wolfsburg to Vienna, with a new semi-dry brake system that combines hydraulic front brakes and electromechanical rear brakes. Based on the ID. Polo, the car uses the current-generation MK C2 one box system and optimized hydraulic calipers on the front axle, while AUMOVIO’s near-production electromechanical brake (EMB) handles the rear axle. The company says both axles run a larger air gap between the brake disc and pad than the production vehicle, further reducing unwanted friction in the wheel brakes.
Highlights
- Front axle: The MK C2 brake-by-wire one box system pairs with a hydraulic caliper that builds a larger air gap more quickly than the series ID. Polo caliper.
- Rear axle: Near-production electromechanical calipers require no hydraulic lines or brake fluid and actively hold the air gap constant.
- Efficiency records: Volkswagen reports 10.4 kWh per 100 miles (6.48 kWh/100 km) on an ideal drive and 12.1 kWh per 100 miles (7.51 kWh/100 km) on a road drive, including charging losses.
- No memory effect: The rear caliper is deliberately reopened after the electric parking brake or high braking forces are applied.
Reduced Residual Braking Torque on the Front Axle
AUMOVIO already supplies the MK C2 and front axle calipers for the series-production ID. Polo. The system is designed entirely to support regenerative braking. As a brake-by-wire solution, it transmits the braking command electronically and is completely decoupled from the hydraulic system.
According to the company, this is the key difference from electric brake boosters, which remain connected to the hydraulic system. The decoupling allows regenerative braking without friction losses.
The system decides on its own whether to engage the friction brake or route the braking command to recover energy through the electric generator. For the Mission Efficiency project vehicle, AUMOVIO also optimized the hydraulic front caliper. Compared with the series model, it can build a larger air gap more quickly, minimizing residual braking torque.
Electromechanical Rear Brakes Hold a Constant Air Gap
The electromechanical rear brakes are new relative to the standard ID. Polo braking system, creating the semi-dry configuration. Instead of hydraulic pressure (“wet” brakes), an electric motor actuates the calipers (“dry” brakes), eliminating hydraulic lines and brake fluid at the rear.
Faster electromechanical actuation allows an even larger air gap than on the front calipers, further reducing residual braking torque. The electric motor can also actively adjust the air gap to keep it constant.
After the electric parking brake is applied or high braking forces are used, the caliper is deliberately reopened regardless of the previous application. AUMOVIO says this eliminates the memory effect seen with hydraulic brakes, in which residual braking torque stays elevated after heavy braking and consumes energy.
“Especially with electric vehicles, energy efficiency is one of the key drivers of development for greater range and lower energy consumption. The braking system can contribute in many different ways as well. To this end, we draw on our 120 years of experience in development. Volkswagen’s ‘Mission Efficiency’ demonstrates that the journey toward greater energy efficiency in electric vehicles is far from over,” said Boris Mergell, Head of the Safety and Motion business area at AUMOVIO.
What Else Can a Semi-Dry Brake System Offer?
Beyond the study’s efficiency focus, AUMOVIO identifies further potential in the semi-dry architecture:
- Driving dynamics: The EMB can distribute brake forces dynamically and individually to each wheel, which the company says improves regenerative braking performance, increases stability during cornering, and enhances braking comfort. AUMOVIO notes the effect can be amplified in a fully dry system with electromechanical calipers at all four wheels.
- Situational air gap control: The EMB widens the air gap during cornering to reduce residual braking torque, and narrows it when hazardous situations are detected early so the vehicle can stop more quickly.
- Weight and maintenance: With no hydraulic lines or brake fluid at the rear, weight can be reduced depending on the model, and brake maintenance requirements are lowered.
- Packaging: The company says design flexibility in vehicle architecture increases.
AUMOVIO’s “Smart Sizing” Caliper Concept
AUMOVIO also outlined its “smart sizing” concept as an example of an optimized hydraulic application. The company has refined the caliper design for electric vehicles, streamlining and reducing the number of components.
A smaller housing and adjusted pad mass reduce caliper weight, and the design allows a greater air gap to cut residual braking torque. Because the brake engages further outward on a larger, thinner disc, less clamping force is required to achieve the same braking torque.
Mission Efficiency’s Three Records
According to Volkswagen, the Mission Efficiency study recently set three world records using new technologies such as a solar roof and adaptations of mass-production technology, including the MK C2:
- Aerodynamics: More aerodynamic than any other car ever approved for road use.
- Ideal drive: 10.4 kWh per 100 miles (6.48 kWh/100 km), measured without inclines or auxiliary consumers.
- Road drive: 12.1 kWh per 100 miles (7.51 kWh/100 km) including charging losses, or 11.1 kWh per 100 miles (6.89 kWh/100 km) excluding them, on a route from the Volkswagen Development Center in Wolfsburg, Germany, through Poznań, Poland, and Olomouc, Czech Republic, to Vienna, Austria.
