They say the wheel is one of man’s oldest inventions. Today, they are still round, and they still roll. It is the technology that stops them that keeps changing. Most automotive braking systems still use friction to stop a vehicle. But friction creates heat, which wastes a good deal of the energy generated. However, new research may lead to friction-less, super-efficient brakes that are especially useful for hybrids and electric vehicles with regenerating braking systems.
Batteries store energy too slowly
Some hybrid and electric vehicles have regenerating brakes, meaning that when the driver brakes, the kinetic motion of the vehicle is captured by the motor, acting as a generator. The captured energy is then stored in the vehicle’s battery pack. However, batteries take time to charge, and so the transferred energy is not sufficient to stop the vehicle without the addition of traditional friction brakes.
Rajesh Rajamani, a mechanical engineering professor at the University of Minnesota, explained:
“Batteries cannot rapidly harvest or supply energy. When a vehicle has to brake quickly, frictional brakes have to be used in addition to electromagnetic brakes, because the electromagnetic brakes cannot charge a battery quickly enough to decelerate the vehicle as rapidly as the driver wants. Unlike batteries, a supercapacitor can harvest and supply energy very quickly.”
New supercapacitor eliminates friction
According to Psyorg, researchers at the University of Minnesota and University of North Texas are developing a supercapacitor that could eventually make friction brakes a thing of the past. Batteries use chemicals and store energy slowly. Supercapacitors use electrical fields to store energy. They can be charged very quickly. They also discharge their energy rapidly. With no heat lost to friction, they have the potential to totally supplant friction brakes in the future.
Light, thin, flexible
Modern supercapacitors use hazardous liquid electrolytes that require bulky protection, adding weight and minimizing flexibility. The new supercapacitors being developed use carbon nanotube-coated cotton paper, making them extremely lightweight, thin and flexible. According to Psyorg, they can fit anywhere in an automobile body without creating design issues.
Modern friction brakes use parts made of heavy cast iron. When that weight rotates with the wheels, it creates what engineers call “unsprung weight.” By eliminating this moving mass, performance and handling will also improve in the vehicle.
The heat generated by friction brakes also causes wear. According to Motor Authority, it is not rare for brake pads and rotors to be replaced more than once during 24-hour endurance competitions. If those friction brakes could be replaced with a friction-free electromagnetic system, little wear, if any, would occur.
Researchers say that the biggest disappointment experienced with the new supercapacitor is that is slower to charge than other supercapicitors being used today. Researchers believe, however, that this problem can be minimized with a nanotube coating of higher density.