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What is regenerative braking?

You've probably heard of the term ‘regenerative braking' which has become commonplace in both hybrid and conventional vehicles. However just what is regenerative braking, how does it work and how does it help the environment? This guide to regenerative braking will explain all.

Regenerative braking from Bosch.

What is regenerative braking?

In the effort to produce greener cars numerous processes have been examined that effect fuel consumption. One process is braking - traditional braking wastes energy because it kills the momentum that the engine has built up.

However, with the process of regenerative braking, this energy effectively finds a new home. Instead of being lost as heat in the brakes, the energy is used to drive an alternator which allows the energy to be partially recovered and stored in a battery.

In conventional vehicles this stored energy is then used to power electrical components including headlights, stereos and air conditioning.

In hybrid cars, regenerative braking is used to charge the battery that propels the electric motor. This is particularly advantageous in town driving situations when cars traditionally travel at low speeds. With regenerative braking a hybrid can rely solely on the electric motor in these situations, therefore producing zero emissions.

Regenerative braking is sometimes confused with dynamic braking but the processes are very different. By contrast, dynamic braking dissipates the energy as heat and does not recapture it.

What are the pros and cons of regenerative braking?

The advantages of regenerative braking are clear-cut as effectively drivers can enjoy ‘something for nothing'. They will notice no difference to regular braking and yet enjoy better fuel economy, reduced CO2 emissions and know that they are saving energy.

Effectively the electric motor works in reverse during the process of regenerative braking. The motor acts as the generator to recharge batteries with the energy that would normally be lost. This reduces the reliance on fuel, boosting economy and lowering emissions.

The main issue with regenerative braking is that it still relies on friction braking too. For example, if used alone the effect of regenerative braking is dramatically cut at lower speeds. Consequently the friction brake is still necessary to bring the vehicle to a complete halt. Friction brakes will always be necessary alongside regenerative brakes just in case the system suffers a failure.

There's still room for improvement with regenerative braking too. In conventional vehicles there is an additional cost and a reliance on the second engine - the electric motor - to reach its full potential. The amount of electrical energy that can be dissipated is also restricted by the capacity of the supply system. As a consequence, dynamic braking is often included alongside regenerative braking to increase the absorption of excess energy.

Which green cars use regenerative braking?

Any current hybrid car will make use of regenerative braking. Some of the earliest examples of hybrids using the system include the Toyota Prius, the Honda Civic hybrid, the Lexus RX 400h and the GS 450h.

Regenerative braking is also crucial to the development of cars using compressed air. Compressed air cars have a similar range to electric vehicles with zero emissions. Compressed air engines reduce the cost of vehicle production by around 20 per cent as there is no need for a fuel tank, cooling system, spark plugs or silencers.

In addition, regenerative braking systems will soon be vital in the sport of motor racing. All cars must become hybrid by 2013 according to regulations by the FIA with regenerative braking used alongside a kinetic energy recovery system.

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Lee Sibbald

Filed under: Guides

1 comment

Mick Cooper

What about listing compressed air hybrids in your poll?

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