What’s a hybrid?

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It’s hard to believe now, but hybrid cars – vehicles such as the Toyota Prius – once were considered exotics with mysteriously complicated powertrains.

True, the hybrid powertrain is a bit complex. But the cars, which debuted in the U.S. in 1999 with the first generation Honda Insight, followed rapidly by rival Toyota’s Prius, are now commonplace. with dozens of models on the market.

Still, it’s nice to know what’s under the hood, and elsewhere.

A hybrid vehicle is simply defined as a one that uses two (or more) different power systems, typically an internal combustion engine and one or more electric motors.

It stores energy for the electric motor in a battery that is much smaller than the batteries in plug-in vehicles with grid-rechargeable battery packs. A hybrid’s battery is recharged via regenerative braking and power from the internal combustion engine.

There are several types of hybrid systems, although the exact type is of little concern to most hybrid vehicle buyers as long as the vehicle fits their needs and delivers the desired level of fuel efficiency.

A parallel hybrid couples the gas engine and electric motor in such a way that they work together, with the gas engine connected directly to the wheels and drawing extra power, when needed, from the electric motor. The battery pack is recharged via regenerative braking.

Through the Road (TTR)hybrids are a type of parallel hybrid in which the gas engine drives one set of wheels while an electric motor provides tower to the other set. The 2018 Acura NSX, with twin electric motors driving the front wheels, is an example.

There also are series-parallel hybrids – the most common type –  in which power is apportioned between gas and electric drives for the best fuel efficiency and power delivery. Series-parallel hybrids can run in all-electric mode, all gas mode or any blend of the two, as the power management system determines. The internal combustion engine also serves as a generator when need to provide additional juice to the electric motor.

A series hybrid, such as the BMW i3 REx (range-extended) is driven exclusively by its electric motor but has an on-board generator of some type to provide juice to the motor.

Plug-in hybrids, which can use any of the three main types of hybrid drive systems, are explained in a separate article.