Continental is promising improved braking efficiency combined with weight reduction as well as lower maintenance costs for its so-called ‘New Wheel Concept’ revealed at its recent technical show in Germany.
Designed specifically for electric vehicles (EV), the New Wheel Concept actually isn’t new. Readers with long memories will recall that the original Audi A8 featured an annular brake concept from Alfred Teves, which Continental bought in 1998, whilst Quebec-based NewTech licensed a similar concept to Visteon in 2000.
The wheel rim consists of two aluminum (AL) parts, the inner AL carrier star with the AL brake disk and the outer AL rim well with the tire. Unlike a conventional disc brake, the New Wheel Concept brake engages the AL disk from the inside. This allows it to have a particularly large diameter, enhancing braking performance.
According to Paul Linhoff, Continental’s head of brake pre-development in the chassis and safety business unit, the friction radius is increased by 40% with a comparable reduction in clamping forces and energy consumption resulting in a down-sizing of ancillary brake components for further weight-saving and improved packaging.
The wheel consists of two parts: the aluminum carrier star, which is permanently bolted to the wheel hub, and the rim well, 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 allows a wider brake disk friction radius, as the space available in the wheel is optimally utilized.
“The system is about two to 5.5 lb lighter than a comparable conventional brake set-up, but we’ve still got some way to go before it is fully optimized,” Linhoff told Automotive Engineering.
The New Wheel Concept uses the strengths of lightweight AL material for the brake, although Continental refused to reveal what grade was used. Thanks to the long leverage effect on the large brake disk, relatively low clamping forces are enough to provide a high level of braking efficiency – and as aluminum is a good heat conductor, the heat generated in the disk during braking is quickly dissipated.
Moreover as aluminum doesn’t rust, the disc will last the lifetime of the vehicle, with only the pads requiring replacement, “We expect the initial higher costs to be offset by the improved service life,” explained a Continental engineer.
Linhoff said it is “crucial” that EV drivers expend minimum energy as possible on the friction brake: “During deceleration, the vehicle’s momentum is converted into electricity by 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 electric motor’s deceleration torque is only no longer sufficient by itself when the driver brakes harder or braking has to carried out with the non-driven axle for reasons of driving dynamics which is when the wheel brake is needed and 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,” added Linhoff.
Continental has been developing the New Wheel concept for the past two-to-three years and it has now been handed over to the business unit for future applications with OEMs expected around the 2020 timeframe. Although primarily aimed at the EV sector, Continental engineers refused to rule out the possibility that it would find applications in combustion-engine vehicles as well.