Continental has expanded its solutions portfolio for electric vehicles, developing an all-new wheel concept to meet the specific requirements of these vehicles. The wheel rim consists of two aluminium (Al) parts, the inner Al carrier star with the Al brake disc and the outer Al rim well with the tyre. In contrast to conventional brakes, the new wheel concept brake engages the Al disc from the inside, which allows it to have a particularly large diameter, which improves braking performance.
To increase the vehicle’s range, deceleration in the EV generates as much electricity as possible through recuperation (by braking using the electric motor), so the wheel brake is used less frequently. The corrosion-free Al brake disc also prevents the formation of rust, which is normal on cast-iron discs, which can hamper braking performance.
‘Electromobility needs new solutions for braking technology too. 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,’ says Matthias Matic, Head of Continental’s Hydraulic Brake Systems Business Unit.
Thanks to the lightweight material used, the new wheel concept reduces the weight of the wheel and brake, enabling lightweight construction in EVs. Advantages of the concept include easier wheel and brake pad changes, lower wear for the brake discs.
Rethinking the wheel
The new wheel concept is based on a new division between the wheel and the axle. Here the wheel consists of two parts, the aluminium 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 aluminium brake disc, which in turn is bolted to the carrier star. The internal brake permits a wide brake disc friction radius, since the space available in the wheel is optimally utilised. During its development, the wheel concept’s braking performance was initially designed for medium and compact class vehicles. In accordance with today’s requirements for this application, the brake is sturdy and fulfils all the established criteria – although it is used much less frequently in an EV.
‘In EVs, it’s crucial that the driver expends as little energy as possible on the friction brake. During 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,’ says Paul Linhoff, Head of Brake Pre-Development in the Chassis & Safety Business Unit at Continental. The deceleration torque of the electric motor is only no longer sufficient by itself when the driver brakes more energetically, or braking also has to carried out with the non-driven axle for driving dynamics reasons. The wheel brake is needed in this situation – and it must be available.
‘Drivers want to be able to rely on a consistent braking effect – and too much rust on the brake disc in particular can really make this difficult,’ Linhoff emphasizes. The reason behind the reduced performance is less friction between the brake pad and the brake disc. The automatic emergency braking function also has to fully rely on the availability of the friction brake effect.
Material and Design
The design of the new wheel concept uses the strengths of lightweight aluminium material for the brake. Thanks to the long leverage effect on the large brake disc, relatively low clamping forces are enough to provide a high level of braking efficiency – and since aluminium is a very good heat conductor, the heat generated in the disc during braking is quickly dissipated.
Continental assumes, after the results of the initial practical tests, that the Al disc itself is not subject to wear, unlike cast-iron discs. 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. The New Wheel Concept has yet another positive; ‘Because the brake disc is fixed on the outside and the brake engages from the inside, the brake calliper can be designed particularly light and stiff. The force is transmitted largely symmetrically into the centre of the axle, and this has a favourable effect on the noise behaviour of the brake,’ says Linhoff – and that’s a side effect which is particularly attractive in a quiet EV.
Continental will also demonstrate the new wheel concept during the Frankfurt motorshow this year.