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Regenerative Braking - What is it and How Does it Work?

Bradley Jando | Tuesday 17th August 2021 2:25pm

Car Cross Section with Chassis Showing

As Hybrid and Electric Vehicles become more popular more and more drivers are reaping the benefits of regenerative braking. The advanced technology takes a portion of the energy that would normally be lost when braking and uses it to help top up the vehicle’s batteries. But just how does this work? And what does it mean when it comes to brake servicing?

What is regenerative braking?

When a car is moving it builds up kinetic energy, and as the car slows this energy must be transferred somewhere else. In traditional mechanical braking, the kinetic energy will be converted to thermal energy (this is why brake discs become hot over prolonged use), which will then dissipate in the form of waste heat as it cools. Where regenerative braking differs, is that the kinetic energy is instead converted into electrical energy, which can then be stored in the vehicle’s batteries, improving efficiency.

How does regenerative braking work?

When driving a vehicle with an electric drive mode, the electric motor draws power from the battery to turn the wheels. When the driver presses the brake pedal the electronics that control the system can decide the most efficient way to slow the vehicle to maximise electric range. The kinetic energy of the moving vehicle is now used to rotate the electric motor, essentially turning it into a miniature generator. By slowing the vehicle using the motor it begins to produce electricity, rather than consuming it, and the electrical energy that is generated is stored in the vehicles batteries where it can be used to power the vehicle when it accelerates again. Since regenerative braking converts kinetic energy into electricity it is able to slow the vehicle down, in the same way that hydraulic brakes slow down using friction.

Are Hybrids/EVs still fitted with a hydraulic braking system?

While most modern hybrid and electric vehicles mostly rely heavily on regenerative brakes to slow down they are also fitted with hydraulic brakes for a few couple of key reasons:

  • Safety – Although regenerative braking helps to improve the efficiency of electric vehicles, it is unfortunately not always great at slowing cars down quickly. In the event of an emergency stop, hydraulic brakes mean that systems such as ABS and ESP (Stability Control) are still operational for each individual wheel, helping to reduce the risk of skidding.The inclusion of hydraulic brakes also means that in the event of electrical failure, the vehicle can still be slowed to a stop.
  • Stationary Braking – When stopped at a junction, or traffic lights, there will not be any kinetic energy present for the regenerative braking system to convert into electrical energy. In this situation, mechanical brakes would be required to prevent the car from rolling

What does this change for brake servicing?

As the hydraulic brakes in electric vehicles is essentially used as a back-up to the regenerative brakes, they should be used less, and therefore should last longer than in traditional petrol or diesel vehicles. However, this is not always the case – as with less use it can be possible for rust and other contaminants to build up more quickly. A build-up of such contaminants can cause issues within the braking mechanism, from the brake pads and discs, to caliper pistons and slider pins.

To keep your brakes in safe condition regular checks should be carried out across the entire braking system – whether it be a hybrid or electric vehicle, or a traditional combustion engine. If you’re unsure on the condition of your brakes, or would like piece of mind before taking a trip in your vehicle, why not pop down to your local Kwik Fit centre, where you can have a free brake check carried out by one of our trained electric vehicle technicians at a time that suits you.

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