FRANKFURT, Germany—Continental A.G. developed a wheel concept to meet the specific requirements of electric vehicles.
The wheel rim consists of two aluminum parts—the inner aluminum carrier star with an aluminum brake disk and the outer aluminum rim well with the tire.
In contrast to conventional wheel brakes, the concept's brake engages the aluminum disk from the inside. This allows it to have a particularly large diameter, which benefits the braking performance, the company said.
To increase the vehicle's range, deceleration in EVs generates as much electricity as possible through recuperation (braking using the electric motor), so the wheel brake is used less frequently. The corrosion-free aluminum brake disk also prevents the formation of rust which can impair the braking effect.
"Electromobility needs new solutions for braking technology, too," said Matthias Matic, head of Continental's Hydraulic Brake Systems Business Unit. "Using conventional brakes is not very effective in this case. The New Wheel Concept meets all the demands that electric driving places on the brake. We used our braking know-how to develop a solution that provides a consistently reliable braking effect in the electric vehicle."
The concept's lightweight material reduces the weight of the wheel and brake, enabling lightweight construction in EVs, according to Conti, noting the advantages of the concept are easier wheel and brake pad changes and the disk is not subject to wear.
The concept is based on a new division between the wheel and the axle where the wheel consists of two parts—the aluminum carrier star which remains permanently bolted to the wheel hub, and the rim well which is bolted to the star.
The wheel brake is fastened to the wheel carrier of the axle and engages from the inside with an annular aluminum brake disk, which in turn is bolted to the carrier star.
The internal brake permits a wide brake disk friction radius, since the space available in the wheel is optimally utilized, the company said.
During its development, the concept's braking performance initially was designed for medium and compact class vehicles, Conti said. In accordance with today's requirements for this application, the brake is sturdy and fulfills all the established criteria — although it is used much less frequently in an EV, Conti said.
"In EVs, it's crucial that the driver expends as little energy as possible on the friction brake," said Paul Linhoff, head of brake pre-development in Conti's Chassis & Safety Business Unit.
"During a deceleration, the momentum of the vehicle is converted into electricity in the generator to increase the vehicle's range. That's why the driver continues to operate the brake pedal—but it certainly doesn't mean that the wheel brakes are active, too."
The deceleration torque of the electric motor is no longer sufficient by itself when the driver brakes more energetically, or braking has to be carried out with the non-driven axle for driving dynamics reasons. The wheel brake is needed in this situation, he said, and it must be available.
"Drivers want to be able to rely on a consistent braking effect—and too much rust on the brake disk in particular can really make this difficult," Linhoff said. The reason behind the reduced performance is less friction between the brake pad and the brake disk. The automatic emergency braking function also has to fully rely on the availability of the friction brake effect, he noted.
The design of the new wheel concept uses the strengths of lightweight aluminum material for the brake.
The long leverage effect on the large brake disk provides relatively low clamping forces that are enough to provide a high level of braking efficiency, according to Conti. Since aluminum is a very good heat conductor, the heat generated in the disk during braking is quickly dissipated.
Conti said it assumes, after the results of the initial practical tests, that the aluminum disk is not subject to wear, unlike cast-iron disks. With the new concept, abrasion only takes place on the pads and the design of the Concept makes replacing them and the wheels much easier.
"Because the brake disk is fixed on the outside and the brake engages from the inside, the brake caliper can be designed particularly light and stiff. The force is transmitted largely symmetrically into the center of the axle, and this has a favorable effect on the noise behavior of the brake," said Linhoff.
Conti will demonstrate the concept during the International Motor Show (IAA) in Frankfurt/Main in September.