FRNKFURT, Germany — Continental A.G.'s automotive business has designed a brake caliper for use on electric vehicles (EVs) that's measurably lighter than existing designs while offering lower residual brake torque.
The new design, dubbed "Green Caliper," is more compact and lighter than those for conventional vehicles but with the same deceleration power, Conti said. Based on current vehicle development cycles, Conti said it expects the Green Caliper concept could be available on new cars within two to three years.
When used in combination with the brake disc, the lower mass — up to 11 pounds per brake in some cases — and the reduced friction between brake pad and disc contribute to increasing the range of an electric vehicle, Conti claims.
Unlike the brakes in a conventional vehicle, those in an EV are activated much less frequently, as the brake is not needed in up to 80% of all deceleration situations due to recuperation, Conti said.
This does not mean, however, that the Green Caliper has to be able to do less than a conventional brake caliper. On the contrary: Because of the weight of the battery in an electric car, the deceleration performance of the brakes often has to be even higher. At the same time, though, their thermal load is lower because the brake is used much less frequently.
"Increasing efficiency is a primary goal in the optimization of electric vehicles. The lower the loss of electrical energy, the greater the range of the vehicle," Dominik Hiss, head of product center friction brakes, hydraulic brake systems, said.
"Brakes can make a contribution to this that has not been exploited to date. With the new Green Caliper, we are providing a production-ready technology that unlocks additional potential for the range of an electric car."
The Green Caliper design is the result of a system analysis of the brakes in the vehicle. The new fist caliper brake precisely meets the requirements in an electric vehicle.
Up to around 0.3 g of deceleration, in the "comfort' braking range, the foundation brake is hardly needed in an EV, Conti said. The so-called blending area — i.e., the seamless transition between recuperation and foundation brake use controlled by the electronic brake system — occurs beyond this point only.
The foundation brake is active only on its own during emergency braking. The developers at Continental have derived design changes from this changing requirement profile. The Green Caliper's cast iron fist caliper is much more compact, and the brake pads are smaller and thinner, as they wear out 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. 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.
Also, in the interest of driving efficiency, the Green Caliper features an active retraction of the brake pads after each braking action. This reduces the residual brake torque between the pads and the disc to less than 0.2 newton meters, meaning virtually loss-free operation. A further design innovation ensures that the air gap between the pad and disc is larger, and evenly distributed on both sides of the brake.
