How Does Regenerative Braking Work?

Hybrids and all-electric vehicles create their own power for battery recharging through a process known as regenerative braking (regen mode). We’ve explained what regenerative braking is and how the process works in general terms, but many folks are interested in the deeper nuts and bolts of electricity generation. They understand that in a hybrid or all-electric vehicle the word “regenerative,” in terms of regenerative braking, means capturing the vehicle’s momentum (kinetic energy) and turning it into electricity that recharges (regenerates) the onboard battery as the vehicle is slowing down and/or stopping. It is this charged battery that in turn powers the vehicle’s electric traction motor. In an all-electric vehicle, this motor is the sole source of locomotion. In a hybrid, the motor works in partnership with an internal combustion engine. But that motor is not just a source of propulsion, it’s also a generator.

Any permanent magnet motor can operate as either a motor or generator. In all-electrics and hybrids, they are more precisely called a motor/generator (M/G). But the technologically curious want to know more, and they’ll often ask “How, and by what mechanism or process, is the electricity created?” It’s a good question, so before we get started explaining how M/Gs and regenerative braking work in hybrids and electric vehicles, it is important to have basic knowledge about how electricity is generated and how a motor/generator functions.

So How Does a Motor/Generator Work in an Electric or Hybrid Vehicle?
No matter the vehicle design, there must be a mechanical connection between the M/G and the drivetrain. In an all-electric vehicle, there could be an individual M/G at each wheel or a central M/G connected to the drivetrain through a gearbox. In a hybrid, the motor/generator could be an individual component that is driven by an accessory belt from the engine (much like an alternator on a conventional vehicle–this is how the GM BAS system works), it could be a pancake M/G that is bolted between the engine and transmission (this is the most common setup–the Prius, for example), or it could be multiple M/Gs mounted inside the transmission (this is how the two-modes work). In any case, the M/G has to be able to propel the vehicle as well as be driven by the vehicle in regen mode.

Read more: How Does Regenerative Braking Work?