Regenerative braking and electric vehicles

Regenerative braking is common on hybrids and electric vehicles (EVS). Instead of wasting motion as heat, the high-voltage motor that drives the road wheels is used as a generator to convert motion energy into electrical energy that is stored, most commonly, by the vehicle’s highvoltage battery. Some of this regenerated energy can then be used to drive the wheels later.

As regenerative braking does not utilise the separate friction brakes, it is discounted in this feature. Should you be working on a hybrid car, consider that the friction brakes may be operated on a brake-by-wire principle, where there is no physical connection between the brake pedal and the friction brakes. This is because the brake ECU decides whether to employ either regenerative braking, or the friction brakes. In many cases, the friction brakes may be employed only at high speeds, or under heavy braking. Wary of being stranded by running their batteries empty, EV drivers tend to prioritise regenerative braking as much as possible.

These relatively low usage patterns increase the risk of corrosion, and professional mechanics report that corroded and binding brakes are becoming a particular problem for hybrids and EVS. A partial solution has been developed by TRW Automotive, which is marketing Electric Blue branded brake pads for EVS and hybrid vehicles. These are designed to not only be quieter than conventional brake pads (because brake noise is more noticeable on cars that lack background engine noise) but are also less vulnerable to corrosion. Even so, after replacing any brake friction parts on a hybrid, or EV, select the lowest setting for regenerative braking (if possible) and test-drive the car, ensuring that the brakes are applied sufficiently to allow the friction surfaces to engage and bed-in.