In contrast to conventional combustion engines, the brakes in electric cars are applied much less frequently. This is due to the fact that in more than 80 percent of all deceleration situations, the brake is not needed at all thanks to recuperation. This not only slows the vehicle down, but also converts kinetic energy into electricity during deceleration, which is then stored in the vehicle’s battery. The top priority in optimizing electric vehicles is therefore to increase efficiency. The lower the losses from the use of electrical energy, the greater the range of the vehicle.
Thanks to a new brake design from Continental, electric vehicles can now even gain around one percent more range: The Green Caliper, a newly developed brake caliper for disc brakes, is significantly lighter than previous designs and has a lower residual brake torque. In combination with the brake disc, the lower mass – in individual cases up to five kilograms per brake – along with the reduced friction between brake pad and disc contribute to increasing the range of an electric vehicle.
A brake design for more range
The new brake caliper design has been optimized precisely for the changed requirement profile of electric vehicles. Because of the comparatively heavy battery, the deceleration performance of the brakes here usually must be higher than in conventional vehicles. At the same time, their thermal load is lower because the wheel brake is stressed much less frequently in the comfort braking range. Only beyond this point occurs the so-called blending area – which is the seamless transition between recuperation and foundation brake use controlled by the electronic brake system. The foundation brake is only active on its own during emergency braking. As a result, the Green Caliper’s cast-iron fist caliper is much more compact, and the brake pads are smaller and less thick because they wear more slowly. Thus, the mass of the caliper is reduced. At the same time, the smaller brake caliper with its lower bridge height enables the installation of a larger cast iron brake disc. Due to the reduced thermal load, the disc can be made significantly thinner, which saves further weight.
Longer lever and smaller residual brake torque
Since the brake engages further out on the larger disc and thus achieves high deceleration power with the same clamping force due to the longer lever arm, the braking performance is optimal at the same time. In addition, the Green Caliper has an active retraction of the brake pads after each braking action. This reduces the brake grinding torque between the pads and the disc to less than 0.2 Newton meters, which means virtually loss-free operation. Although this increases the distance between the pads and the brake disc, in combination with the MK C2 brake-by-wire brake system and Continental's electronic pedal this longer travel - in the interest of low residual drag torque – is not noticeable on the brake pedal. The compromise between pedal feel and residual torque that is otherwise necessary with every brake does not apply here. The Green Caliper construction represents a production-ready technology that opens up additional potential for the range of an electric car and can now be integrated into vehicles with the usual lead time for application development of two to three years.