Regenerative braking

A regenerative brake is an energy recovery mechanism which slows a vehicle or object by converting its kinetic energy into a form which can be either used immediately or stored until needed. This contrasts with conventional braking systems, where the excess kinetic energy is converted to unwanted and wasted heat by friction in the brakes. In addition to improving the overall efficiency of the vehicle, regeneration can greatly extend the life of the braking system as its parts do not wear as quickly.

The most common form of regenerative brake involves an electric motor as an electric generator. In electric railways the electricity generated is fed back into the supply system. In battery electric and hybrid electric vehicles, the energy is stored chemically in a battery, electrically in a bank of capacitors, or mechanically in a rotating flywheel. Hydraulic hybrid vehicles use hydraulic motors to store energy in the form of compressed air.

Regenerative braking is not by itself sufficient as the sole means of safely bringing a vehicle to a standstill, or slowing it as required so it must be used in conjunction with another braking system such as friction-based braking.

Regenerative and friction braking must both be used, creating the need to control them to produce the required total braking. The GM EV-1 was the first commercial car to do this. In 1997 and 1998 engineers Abraham Farag and Loren Majersik were issued two patents for this brake-by-wire technology.

Early applications commonly suffered from a serious safety hazard: in many early electric vehicles with regenerative braking, the same controller positions were used to apply power and to apply the regenerative brake, with the functions being swapped by a separate manual switch. This led to a number of serious accidents when drivers accidentally accelerated when intending to brake, such as the runaway train accident in Wädenswil, Switzerland in 1948, which killed twenty-one people.

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Wikipedia